| Loads: | Methods: | Other keywords: | Year: |
|
|
|
|
|
Authors: Xuguang Wang; Robin E. Kim, Ph.D.; Oh-Sung Kwon, Ph.D., M.ASCE; and Inhwan Yeo, Ph.D.
DOI: 10.1061/(ASCE)ST.1943-541X.0002113
Abstract: This paper presents a hybrid fire simulation method for civil structures in which a critical element subject to fire is experimentally tested while the remaining structural system is numerically analyzed simultaneously. The proposed method is different from previous approaches in that it is fully validated with full-scale specimen subjected to high temperature and that it is an automated displacement controlled test with deformation error compensation. The two substructures (i.e., an experimental model and a numerical model) are integrated through network to enforce displacement compatibility and force equilibrium. Then, the developed simulation method is applied to a fire simulation of a steel moment resisting frame where one of the columns is assumed to be under temperature load following ISO 834-11:2014 fire curve. The results show that the proposed hybrid simulation method can replicate the numerical prediction, and thus can be applied to more challenging structural systems such as the structural behavior under fire load, which is computationally difficult using numerical models.
Keywords: Fire, Hybrid Simulation, Experimental
Authors: Michael L. Whiteman; Pedro L. Fernández-Cabán; Brian M. Phillips; Forrest J. Masters; Jennifer A. Bridge; and Justin R. Davis
DOI: 10.3389/fbuil.2018.00013
Abstract: This paper explores the use of a cyber-physical systems (CPS) “loop-in-the-model” approach to optimally design the envelope and structural system of low-rise buildings subject to wind loads. Both the components and cladding (C&C) and the main wind force resisting system (MWFRS) are considered through multi-objective optimization. The CPS approach combines the physical accuracy of wind tunnel testing and efficiency of numerical optimization algorithms to obtain an optimal design. The approach is autonomous: experiments are executed in a boundary layer wind tunnel (BLWT), sensor feedback is monitored and analyzed by a computer, and optimization algorithms dictate physical changes to the structural model in the BLWT through actuators. To explore a CPS approach to multi-objective optimization, a low-rise building with a parapet wall of variable height is considered. In the BLWT, servo-motors are used to adjust the parapet to a particular height. Parapet walls alter the location of the roof corner vortices, reducing suction loads on the windward facing roof corners and edges, a C&C design load. At the same time, parapet walls increase the surface area of the building, leading to an increase in demand on the MWFRS. A combination of non-stochastic and stochastic optimization algorithms were implemented to minimize the magnitude of suction and positive pressures on the roof of a low-rise building model, followed by stochastic multi objective optimization to simultaneously minimize the magnitude of suction pressures and base shear. Experiments were conducted at the University of Florida Experimental Facility (UFEF) of the National Science Foundation’s (NSF) Natural Hazard Engineering Research Infrastructure (NHERI) program.
Keywords: Wind, Algorithms, Experimental
Authors: Li-Qiao Lu; Jin-Ting Wang; and Fei Zhu
DOI: 10.1080/13632469.2018.1469442
Abstract: This paper proposes a novel framework to efficiently calculate a large-scale finite element (FE) numerical substructure in real-time hybrid simulation (RTHS). It is composed of a non-real-time Windows computer and a real-time Target Computer. The Windows computer is used to solve the FE numerical substructure by parallel computing in soft real-time, while the real-time Target Computer generates displacement signals for the controller in real time. Based on the proposed framework, a RTHS with numerical substructure simulated in Windows environment is developed. It is demonstrated that the computational efficiency of the RTHS could be greatly improved by parallel programming.
Keywords: RTHS, Large Scale
Authors: C. Kolay; J.M. Ricles; T.M. Marullo; S. Al-Subaihawi; and S.E. Quiel
DOI: 10.4028/www.scientific.net/KEM.763.566
Abstract: The essence of real-time hybrid simulation (RTHS) is its ability to combine the benefits of physical testing with those of computational simulations. Therefore, an understanding of the real-time computational issues and challenges is important, especially for RTHS of large systems, in advancing the state of the art. To this end, RTHS of a 40-story (plus 4 basement stories) tall building having nonlinear energy dissipation devices for mitigation of multiple natural hazards, including earthquake and wind events, were conducted at the NHERI Lehigh Experimental Facility. An efficient implementation procedure of the recently proposed explicit modified KR-α (MKR-α) method was developed for performing the RTHS. This paper discusses this implementation procedure and the real-time computational issues and challenges with regard to this implementation procedure. Some results from the RTHS involving earthquake loading are presented to highlight the need for and application of RTHS in performance based design of tall buildings under earthquake hazard.
Keywords: Earthquake, Wind, RTHS, Nonlinear, Large Scale, Experimental
Authors: Maikol Del Carpio R.; M. Javad Hashemi; and Gilberto Mosqueda
DOI: 10.1007/s11803-017-0411-z
Abstract: This study examines the performance of integration methods for hybrid simulation of large and complex structural systems in the context of structural collapse due to seismic excitations. The target application is not necessarily for real-time testing, but rather for models that involve large-scale physical sub-structures and highly nonlinear numerical models. Four case studies are presented and discussed. In the first case study, the accuracy of integration schemes including two widely used methods, namely, modified version of the implicit Newmark with fixed-number of iteration (iterative) and the operator-splitting (non-iterative) is examined through pure numerical simulations. The second case study presents the results of 10 hybrid simulations repeated with the two aforementioned integration methods considering various time steps and fixed-number of iterations for the iterative integration method. The physical sub-structure in these tests consists of a single-degree-of-freedom (SDOF) cantilever column with replaceable steel coupons that provides repeatable highly nonlinear behavior including fracture-type strength and stiffness degradations. In case study three, the implicit Newmark with fixed-number of iterations is applied for hybrid simulations of a 1:2 scale steel moment frame that includes a relatively complex nonlinear numerical substructure. Lastly, a more complex numerical substructure is considered by constructing a nonlinear computational model of a moment frame coupled to a hybrid model of a 1:2 scale steel gravity frame. The last two case studies are conducted on the same porotype structure and the selection of time steps and fixed number of iterations are closely examined in pre-test simulations. The generated unbalance forces is used as an index to track the equilibrium error and predict the accuracy and stability of the simulations
Keywords: Earthquake, Hybrid Simulation, Nonlinear, Large Scale, Case Study
Authors: Amin Maghareh; Christian E. Silva; and Shirley J. Dyke
DOI: 10.1016/j.ymssp.2017.07.022
Abstract: Hydraulic actuators have been widely used to experimentally examine structural behavior at multiple scales. Real-time hybrid simulation (RTHS) is one innovative testing method that largely relies on such servo-hydraulic actuators. In RTHS, interface conditions must be enforced in real time, and controllers are often used to achieve tracking of the desired displacements. Thus, neglecting the dynamics of hydraulic transfer system may result either in system instability or sub-optimal performance. Herein, we propose a nonlinear dynamical model for a servo-hydraulic actuator (a.k.a. hydraulic transfer system) coupled with a nonlinear physical specimen. The nonlinear dynamical model is transformed into controllable canonical form for further tracking control design purposes. Through a number of experiments, the controllable canonical model is validated.
Keywords: RTHS, Nonlinear, Experimental, Transfer Systems
Authors: Gaston A. Fermandois and Billie F. Spencer, Jr.
DOI: 10.1007/s11803-017-0407-8
Abstract: Real-time hybrid simulation is an efficient and cost-effective dynamic testing technique for performance evaluation of structural systems subjected to earthquake loading with rate-dependent behavior. A loading assembly with multiple actuators is required to impose realistic boundary conditions on physical specimens. However, such a testing system is expected to exhibit significant dynamic coupling of the actuators and suffer from time lags that are associated with the dynamics of the servo-hydraulic system, as well as control-structure interaction (CSI). One approach to reducing experimental errors considers a multi-input, multi-output (MIMO) controller design, yielding accurate reference tracking and noise rejection. In this paper, a framework for multi-axial real-time hybrid simulation (maRTHS) testing is presented. The methodology employs a real-time feedback-feedforward controller for multiple actuators commanded in Cartesian coordinates. Kinematic transformations between actuator space and Cartesian space are derived for all six-degrees-of freedom of the moving platform. Then, a frequency domain identification technique is used to develop an accurate MIMO transfer function of the system. Further, a Cartesian-domain model-based feedforward-feedback controller is implemented for time lag compensation and to increase the robustness of the reference tracking for given model uncertainty. The framework is implemented using the 1/5th-scale Load and Boundary Condition Box (LBCB) located at the University of Illinois at Urbana-Champaign. To demonstrate the efficacy of the proposed methodology, a single-story frame subjected to earthquake loading is tested. One of the columns in the frame is represented physically in the laboratory as a cantilevered steel column. For real time execution, the numerical substructure, kinematic transformations, and controllers are implemented on a digital signal processor. Results show excellent performance of the maRTHS framework when six-degrees-of-freedom are controlled at the interface between substructures
Keywords: Earthquake, RTHS, UQ, Experimental, Controller Design
Authors: Ge Ou; Shirley J. Dyke; and Arun Prakash
DOI: 10.1016/j.ymssp.2016.06.015
Abstract: In conventional hybrid simulation (HS) and real time hybrid simulation (RTHS) applications, the information exchanged between the experimental substructure and numerical substructure is typically restricted to the interface boundary conditions (force, displacement, acceleration, etc.). With additional demands being placed on RTHS and recent advances in recursive system identification techniques, an opportunity arises to improve the fidelity by extracting information from the experimental substructure. Online model updating algorithms enable the numerical model of components (herein named the target model), that are similar to the physical specimen to be modified accordingly. This manuscript demonstrates the power of integrating a model updating algorithm into RTHS (RTHSMU) and explores the possible challenges of this approach through a practical simulation. Two Bouc–Wen models with varying levels of complexity are used as target models to validate the concept and evaluate the performance of this approach. The constrained unscented Kalman filter (CUKF) is selected for using in the model updating algorithm. The accuracy of RTHSMU is evaluated through an estimation output error indicator, a model updating output error indicator, and a system identification error indicator. The results illustrate that, under applicable constraints, by integrating model updating into RTHS, the global response accuracy can be improved when the target model is unknown. A discussion on model updating parameter sensitivity to updating accuracy is also presented to provide guidance for potential users
Keywords: Hybrid Simulation, Model Updating, Algorithms, Experimental
Authors: Ruiyang Zhang; Brian M. Phillips; Shun Taniguchi; Masahiro Ikenaga; and Kohju Ikago
DOI: 10.1002/stc.1971
Abstract: Interstory isolation systems have recently gained popularity as an alternative for seismic protection, especially in densely populated areas. In inter‐story isolation, the isolation system is incorporated between stories instead of the base of the structure. Installing inter‐story isolation is simple, inexpensive, and disruption free in retrofit applications. Benefits include nominally independent structural systems where the accelerations of the added floors are reduced when compared to a conventional structural system. Furthermore, the base shear demand on the total structure is not significantly increased. Practical applications of inter‐story isolation have appeared in the United States, Japan, and China, and likewise new design validation techniques are needed to parallel growing interest. Real‐time hybrid simulation (RTHS) offers an alternative to investigate the performance of buildings with inter‐story isolation. Shake tables, standard equipment in many laboratories, are capable of providing the interface boundary conditions necessary for this application of RTHS. The substructure below the isolation layer can be simulated numerically while the superstructure above the isolation layer can be tested experimentally. This configuration provides a high‐fidelity representation of the nonlinearities in the isolation layer, including any supplemental damping devices. This research investigates the seismic performance of a 14‐story building with inter‐story isolation. A model‐based acceleration‐tracking approach is adopted to control the shake table, exhibiting good offline and online acceleration tracking performance. The proposed methods demonstrate that RTHS is an accurate and reliable means to investigate buildings with inter‐story isolation, including new configurations and supplemental control approaches.
Keywords: RTHS, Nonlinear, Large Scale, Experimental
Authors: Xin Li; Ali I. Ozdagli; Shirley J. Dyke, A.M.ASCE; Xilin Lu; and Richard Christenson, M.ASCE
DOI: 10.1061/(ASCE)CP.1943-5487.0000654
Abstract: Hybrid simulation combines numerical simulation and physical testing, and is thus considered to be an efficient alternative to traditional testing methodologies in the evaluation of global performance of large or complex structures. Real-time hybrid simulation (RTHS) is performed when it is important to fully capture rate-dependent behaviors in the physical substructure. Although the demand to test more complex systems grows, not every laboratory has the right combination of computational and equipment resources available to perform largescale experiments. Distributed real-time hybrid simulation (dRTHS) facilitates testing that is to be conducted at multiple geographically distributed laboratories while utilizing the Internet to couple the substructures. One major challenge in dRTHS is to accommodate the unpredictable communication time delays between the various distributed sites that occur as a result of Internet congestion. Herein, a dRTHS framework is proposed where a modified Smith predictor is adopted to accommodate such communication delays. To examine and demonstrate the sensitivity of the proposed framework to communication delays and to modeling errors, parametric analytical case studies are presented. Additionally, the effectiveness of this dRTHS framework is verified through successful execution of multisite experiments. The results demonstrate that this framework provides a new option for researchers to evaluate the global response of structural systems in a distributed real-time environment.
Keywords: RTHS, Large Scale, Experimental, Case Study
Authors: Chinmoy Kolay, A.M.ASCE; and James M. Ricles
DOI: 10.1061/(ASCE)ST.1943-541X.0001944
Abstract: Existing state determination procedures for force-based finite elements use either an iterative scheme at the element level or a noniterative scheme at the element level that relies on an iterative solution algorithm for the global equilibrium equations. The former cannot ensure convergence in real-time computations, whereas the latter requires an implicit direct integration algorithm; therefore, these procedures are not applicable to real-time hybrid simulation (RTHS) utilizing an explicit direct integration algorithm. A new procedure is developed based on a fixed number of iterations and an unconditionally stable explicit model-based integration algorithm. If the maximum number of iterations is reached, element resisting forces are corrected to re-establish compatibility, and unbalanced section forces are carried over to and corrected in the next time step. This procedure is used in the numerical simulation and RTHS of an earthquake-excited two-story reinforced concrete building. Results show that an accurate solution can be obtained even without performing any iteration. The influence of the model-based parameters of the integration algorithm on the stability and accuracy of the RTHS is also studied.
Keywords: Earthquake, RTHS, Algorithms, Experimental
Authors: Mark Laier Brodersen; Ge Ou, Jan Høgsberg; and Shirley Dyke
DOI: 10.1016/j.engstruct.2016.08.020
Abstract: Results from real time hybrid simulations are compared to full numerical simulations for a hybrid viscous damper, composed of a viscous dashpot in series with an active actuator and a load cell. By controlling the actuator displacement via filtered integral force feedback the damping performance of the hybrid viscous damper is improved, while for pure integral force feedback the damper stroke is instead increased. In the real time hybrid simulations viscous damping is emulated by a bang-bang controlled Magneto-Rheological (MR) damper. The controller activates high-frequency modes and generates drift in the actuator displacement, and only a fraction of the measured damper force can therefore be used as input to the investigated integral force feedback in the real time hybrid simulations.
Keywords: RTHS, Experimental
Authors: Pengfei Shi; Bin Wu; Billie F. Spencer Jr.; Brian M. Phillips; and Chia-Ming Chang
DOI: 10.1002/stc.1808
Abstract: The equivalent force control (EFC) method has been developed for real-time hybrid testing to replace the numerical iteration of implicit integration with a force-feedback control loop. With this control loop, the EFC method can also compensate for the time delay in real-time hybrid testing. However, the delay compensation effect of the EFC can be influenced by factors such as noises in the measured displacement. This paper discusses the influence of the measurement noises on real-time hybrid testing with the EFC. The Kalman filter is proposed to filter the noises in the measured actuator displacement for improved performance. A higher proportional gain in the PID controller, which improves the effect of time delay compensation of the EFC method, can be allowed without losing stability when incorporating the Kalman filter. A series of real-time hybrid tests were conducted, and the results validated that the EFC method with Kalman filter can effectively compensate for the time delay.
Keywords: Earthquake, RTHS, Experimental
Authors: Fei Zhu; Jin-Ting Wang; Feng Jin; and Yao Gui
DOI: 10.1007/s10518-015-9816-0
Abstract: Real-time hybrid simulation (RTHS) combines physical experimentation with numerical simulation to evaluate dynamic responses of structures. The inherent characteristics of integration algorithms change when simulating numerical substructures owing to the response delay of loading systems in physical substructures. This study comprehensively investigates the effects of integration algorithms on the delay-dependent stability and accuracy of multiple degrees-of-freedom RTHS systems. Seven explicit integration algorithms are considered; and the discrete-time root locus technique is adopted. It is found that the stability of RTHS system is mainly determined by the time delay rather than the integration algorithms, whereas its accuracy mainly depends on the accuracy characteristic of the applied integration algorithm itself. An unconditionally stable integration algorithm cannot always guarantee good stability performance; and the inherent accuracy or numerical energy dissipation of integration algorithms should be taken into account in RTHSs. These theoretical findings are well verified by RTHSs.
Keywords: RTHS, Algorithms, Experimental
Authors: Saeid Mojiri; Oh-Sung Kwon; and Constantin Christopoulos
DOI: 10.1002/eqe.3155
Abstract: This paper presents a ten‐element hybrid (experimental‐numerical) simulation platform, referred to as UT10, which was developed for running hybrid simulations of braced frames with up to ten large‐capacity physical brace specimens. This paper presents the details of the development of different components of UT10 and an adjustable yielding brace (AYB) specimen, which was designed to perform hybrid simulations with UT10. As the first application of UT10, a five‐story buckling‐restrained braced frame and a special concentrically braced frame (BRBF and SCBF) were designed and tested with AYB specimens and buckling specimens representing the braces. Cyclic tests of the AYB, one‐ and three‐element hybrid simulations of the BRBF, and four‐element hybrid simulations of the SCBF inside the UT10 confirmed the functionality of UT10 for running hybrid simulations on multiple specimens. The tests also indicated that AYB was capable of producing a stable hysteretic response with characteristics similar to BRBs. Comparison of the results of the hybrid simulations of the BRBF and SCBF with their fully numerical models showed that the modeling inaccuracies of the yielding braces could potentially affect the global response of the multi‐story braced frames further emphasizing the need for experimental calibration or hybrid simulation for achieving more accurate response predictions. UT10 provides a simple and reconfigurable platform that can be used to achieve a realistic understanding of the seismic response of multi‐story frames with yielding braces, distinguish their modeling limitations, and improve different modeling techniques available for their seismic response prediction.
Keywords: Earthquake, Hybrid Simulation, Large Scale, Experimental
Authors: Vahid Sadeghian; Oh-Sung Kwon; and Frank Vecchio
DOI: 10.1016/j.engstruct.2018.12.023
Abstract: This study presents a framework for multi-platform analysis and hybrid simulation of reinforced concrete (RC) structures. In this approach, each subpart of the structure, based on its mechanical characteristics, is modelled using the most suitable finite element analysis tool or represented with a test specimen. The proposed framework combines all the substructure modules and takes into account the interactions between them by satisfying compatibility and equilibrium requirements. The main contribution of the study lies in demonstrating the effectiveness of multi-platform modelling in accurate and practical analysis of complex RC structures or multi-disciplinary RC systems with a particular focus on shear behaviour. Three application examples including a wide-flange shear wall, a three-storey frame with critical joints, and a soil-structure interaction simulation are discussed in detail. It is concluded that the multi-platform analysis can compute the behaviour of such structures with a level of accuracy that was previously difficult to achieve with most single-platform analysis software.
Keywords: Hybrid Simulation, Experimental
Authors: Vahid Sadeghian; Oh-Sung Kwon; and Frank Vecchio
DOI: 10.1007/s11803-017-0410-0
Abstract: This study presents a numerical multi-scale simulation framework which is extended to accommodate hybrid simulation (numerical-experimental integration). The framework is enhanced with a standardized data exchange format and connected to a generalized controller interface program which facilitates communication with various types of laboratory equipment and testing configurations. A small-scale experimental program was conducted using a six degree-of-freedom hydraulic testing equipment to verify the proposed framework and provide additional data for small-scale testing of shearcritical reinforced concrete structures. The specimens were tested in a multi-axial hybrid simulation manner under a reversed cyclic loading condition simulating earthquake forces. The physical models were 1/3.23-scale representations of a beam and two columns. A mixed-type modelling technique was employed to analyze the remainder of the structures. The hybrid simulation results were compared against those obtained from a large-scale test and finite element analyses. The study found that if precautions are taken in preparing model materials and if the shear-related mechanisms are accurately considered in the numerical model, small-scale hybrid simulations can adequately simulate the behaviour of shear-critical structures. Although the findings of the study are promising, to draw general conclusions additional test data are required.
Keywords: Earthquake, Hybrid Simulation, Large Scale, Experimental
Authors: Viswanath Kammula; Jeffrey Erochko; Oh-Sung Kwon; and Constantin Christopoulos
DOI: 10.1002/eqe.2374
Abstract: Substructure hybrid simulation has been the subject of numerous investigations in recent years. The simulation method allows for the assessment of the seismic performance of structures by representing critical components with physical specimens and the rest of the structure with numerical models. In this study the system level performance of a six‐storey structure with telescoping self‐centering energy dissipative (T‐SCED) braces is validated through pseudo‐dynamic (PsD) hybrid simulation. Fragility curves are derived for the T‐SCED system. This paper presents the configuration of the hybrid simulation, the newly developed control software for PsD hybrid simulation, which can integrate generic hydraulic actuators into PsD hybrid simulation, and the seismic performance of a structure equipped with T‐SCED braces. The experimental results show that the six‐storey structure with T‐SCED braces satisfies performance limits specified in ASCE 41.
Keywords: Earthquake, Hybrid Simulation, Experimental
Authors: Oh-Sung Kwon and Viswanath Kammula
DOI: 10.1002/eqe.2307
Abstract: Substructure hybrid simulation has been actively investigated and applied to evaluate the seismic performance of structural systems in recent years. The method allows simulation of structures by representing critical components with physically tested specimens and the rest of the structure with numerical models. However, the number of physical specimens is limited by available experimental equipment. Hence, the benefit of the hybrid simulation diminishes when only a few components in a large system can be realistically represented. The objective of the paper is to overcome the limitation through a novel model updating method. The model updating is carried out by applying calibrated weighting factors at each time step to the alternative numerical models, which encompasses the possible variation in the experimental specimen properties. The concept is proposed and implemented in the hybrid simulation framework, UI‐SimCor. Numerical verification is carried out using two‐DOF systems. The method is also applied to an experimental testing, which proves the concept of the proposed model updating method.
Keywords: Earthquake, Hybrid Simulation, Model Updating, Large Scale, Experimental
Authors: Thomas Sauder; Stefano Marelli; and Asgeir J.Sørensen
DOI: 10.1016/j.automatica.2018.11.040
Abstract: Cyber–physicalempirical methods consist in partitioning a dynamical system under study into a set of physical and numerical substructures that interact in real-time through a control system. In this paper, we define and investigate the fidelity of such methods, that is their capacity to generate systems whose outputs remain close to those of the original system under study. In practice, fidelity is jeopardized by uncertain and heterogeneous artefacts originating from the control system, such as actuator dynamics, time delays and measurement noise. We present a computationally efficient method, based on surrogate modelling and active learning techniques, to (1) verify that a cyber–physical empirical setup achieves probabilistic robust fidelity, and (2) to derive fidelity bounds, which translate to absolute requirements to the control system. For verification purposes, the method is first applied to the study of a simple mechanical system. Its efficiency is then demonstrated on a more complex problem, namely the active truncation of slender marine structures, in which the substructures’ dynamics cannot be described by an analytic solution.
Keywords: Earthquake, Fire, Wind, Wave, RTHS, UQ, Machine Learning, Theory, Algorithms, Case Study, Transfer Systems, Controller Design
Authors: Thomas Sauder; Stefano Marelli; Kjell Larsen; and Asgeir J.Sørensen
DOI: 10.1016/j.apor.2018.02.023
Abstract: Performing hydrodynamic model testing of ultra-deep water floating systems at a reasonable scale is challenging, due to the limited space available in existing laboratories and to the large spatial extent of the slender marine structures that connect the floater to the seabed. In this paper, we consider a method based on real-time hybrid model testing, namely the active truncation of the slender marine structures: while their upper part is modelled physically in an ocean basin, their lower part is simulated by an adequate numerical model. The control system connecting the two substructures inevitably introduces artefacts, such as noise, biases and time delays, whose probabilistic description is assumed to be known. We investigate specifically how these artefacts influence the fidelity of the active truncation setup, that is its capability to reproduce correctly the dynamic behaviour of the system under study. We propose a systematic numerical method to rank the artefacts according to their influence on the fidelity of the test. The method is demonstrated on the active truncation of a taut polyester mooring line.
Keywords: Earthquake, Fire, Wind, Wave, RTHS, UQ, Theory, Algorithms, Transfer Systems, Controller Design
Authors: Oreste S. Bursi; Giuseppe Abbiati; and Md S. Reza
DOI: 10.12989/sss.2014.14.6.1005
Abstract: The need for assessing dynamic response of typical industrial piping systems subjected to seismic loading motivated the authors to apply model reduction techniques to experimental dynamic substructuring. Initially, a better insight into the dynamic response of the emulated system was provided by means of the principal component analysis. The clear understanding of reduction basis requirements paved the way for the implementation of a number of model reduction techniques aimed at extending the applicability range of the hybrid testing technique beyond its traditional scope. Therefore, several hybrid simulations were performed on a typical full-scale industrial piping system endowed with a number of critical components, like elbows, Tee joints and bolted flange joints, ranging from operational to collapse limit states. Then, the favourable performance of the L-Stable Real-Time compatible time integrator and an effective delay compensation method were also checked throughout the testing campaign. Finally, several aspects of the piping performance were commented and conclusions drawn.
Keywords: Earthquake, Hybrid Simulation, Experimental
Authors: Giuseppe Abbiati; Oreste S. Bursi; Philippe Caperan; Luigi Di Sarno; Francisco Javier Molina; Fabrizio Paolacci; and Pierre Pegon
DOI: 10.1002/eqe.2580
Abstract: This paper deals with the seismic response assessment of an old reinforced concrete viaduct and the effectiveness of friction‐based retrofitting systems. Emphasis was laid on an old bridge, not properly designed to resist seismic action, consisting of 12 portal piers that support a 13‐span bay deck for each independent roadway. On the basis of an OpenSEES finite element frame pier model, calibrated in a previous experimental campaign with cyclic displacement on three 1:4 scale frame piers, a more complex experimental activity using hybrid simulation has been devised. The aim of the simulation was twofold: (i) to increase knowledge of non‐linear behavior of reinforced concrete frame piers with plain steel rebars and detailing dating from the late 1950s; and (ii) to study the effectiveness of sliding bearings for seismic response mitigation. Hence, to explore the performance of the as built bridge layout and also of the viaduct retrofitted with friction‐based devices, at both serviceability and ultimate limit state conditions, hybrid simulation tests were carried out. In particular, two frame piers were experimentally controlled with eight‐actuator channels in the as built case while two frame piers and eight sliding bearings were controlled with 18‐actuator channels in the isolated case. The remaining frame piers were part of numerical substructures and were updated offline to accurately track damage evolution.
Keywords: Earthquake, Hybrid Simulation, Nonlinear, Experimental
Authors: Oreste S. Bursi; Giuseppe Abbiati; Enrico Cazzador; Pierre Pegon; and Francisco J. Molina
DOI: 10.1002/nme.5556
Abstract: This article presents a novel approach to model validation and to the calibration of complex structural systems, through the adoption of heterogeneous (numerical/physical) simulation based on dynamic substructuring (HDS). HDS isolates the physical sub‐system (PS) that contains the key region of nonlinear behavior of interest and is tested experimentally, separate from the remainder of the system, that is, the numerical sub‐system (NS), which is numerically simulated. A parallel partitioned time integrator based on the finite element tearing and interconnecting method plays a central role in solving the coupled system response, enabling a rigorous and stable synchronization between sub‐systems and a realistic interaction between PS and numerical sub‐system response. This feature enhances the quality of benchmarks for validation and calibration of low‐discrepancy models through virtual structural testing. As a proof of concept, we select an old reinforced concrete viaduct, subjected to seismic loading. Several HDS were conducted at the European Laboratory for Structural Assessment in Ispra (Italy) considering two physical piers and related concave sliding bearings as PSs of the heterogeneous system. As a result, the benefit of employing HDS to set benchmarks for model validation and calibration is highlighted, by developing low‐discrepancy FE models of critical viaduct components.
Keywords: Nonlinear, Experimental
Authors: Giuseppe Abbiati; Vincenzo La Salandra; Oreste S. Bursi; and Luca Caracoglia
DOI: 10.1016/j.ymssp.2017.07.020
Abstract: Successful online hybrid (numerical/physical) dynamic substructuring simulations have shown their potential in enabling realistic dynamic analysis of almost any type of non-linear structural system (e.g., an as-built/isolated viaduct, a petrochemical piping system subjected to non-stationary seismic loading, etc.). Moreover, owing to faster and more accurate testing equipment, a number of different offline experimental substructuring methods, operating both in time (e.g. the impulse-based substructuring) and frequency domains (i.e. the Lagrange multiplier frequency-based substructuring), have been employed in mechanical engineering to examine dynamic substructure coupling. Numerous studies have dealt with the above-mentioned methods and with consequent uncertainty propagation issues, either associated with experimental errors or modelling assumptions. Nonetheless, a limited number of publications have systematically cross-examined the performance of the various Experimental Dynamic Substructuring (EDS) methods and the possibility of their exploitation in a complementary way to expedite a hybrid experiment/numerical simulation. From this perspective, this paper performs a comparative uncertainty propagation analysis of three EDS algorithms for coupling physical and numerical subdomains with a dual assembly approach based on localized Lagrange multipliers. The main results and comparisons are based on a series of Monte Carlo simulations carried out on a five-DoF linear/non-linear chain-like systems that include typical aleatoric uncertainties emerging from measurement errors and excitation loads. In addition, we propose a new Composite-EDS (C-EDS) method to fuse both online and offline algorithms into a unique simulator. Capitalizing from the results of a more complex case study composed of a coupled isolated tank-piping system, we provide a feasible way to employ the C-EDS method when nonlinearities and multi-point constraints are present in the emulated system.
Keywords: Hybrid Simulation, UQ, Nonlinear, Algorithms, Experimental, Case Study
Authors: Charles-Philippe Lamarche; Robert Tremblay; Pierre Léger; Martin Leclerc; and Oreste S. Bursi
DOI: 10.1002/eqe.994
Abstract: Results from real‐time dynamic substructuring (RTDS) tests are compared with results from shake table tests performed on a two‐storey steel building structure model. At each storey, the structural system consists of a cantilevered steel column resisting lateral loads in bending. In two tests, a slender diagonal tension‐only steel bracing member was added at the first floor to obtain an unsymmetrical system with highly variable stiffness. Only the first‐storey structural components were included in the RTDS test program and a Rosenbrock‐W linearly implicit integration scheme was adopted for the numerical solution. The tests were performed under seismic ground motions exhibiting various amplitude levels and frequency contents to develop first and second mode‐dominated responses as well as elastic and inelastic responses. A chirp signal was also used. Coherent results were obtained between the shake table and the RTDS testing techniques, indicating that RTDS testing methods can be used to successfully reproduce both the linear and nonlinear seismic responses of ductile structural steel seismic force resisting systems. The time delay introduced by actuator‐control systems was also studied and a novel adaptive compensation scheme is proposed.
Keywords: Earthquake, Nonlinear, Large Scale, Experimental
Authors: Oreste S. Bursi; Chuanguo Jia; Leonardo Vulca; Simon A. Neild; and David J. Wagg
DOI: 10.1002/eqe.1017
Abstract: In this paper, Rosenbrock‐based algorithms originally developed for real‐time testing of linear systems with dynamic substructuring are extended for use on nonlinear systems. With this objective in mind and for minimal overhead, both two‐ and three‐stages linearly implicit real‐time compatible algorithms were endowed with the Jacobian matrices requiring only one evaluation at the beginning of each time step. Moreover, these algorithms were improved with subcycling strategies. In detail, the paper briefly introduces Rosenbrock‐based L‐Stable Real‐Time (LSRT) algorithms together with linearly implicit and explicit structural integrators, which are now commonly used to perform real‐time tests. Then, the LSRT algorithms are analysed in terms of linearized stability with reference to an emulated spring pendulum, which was chosen as a nonlinear test problem, because it is able to exhibit a large and relatively slow nonlinear circular motion coupled to an axial motion that can be set to be stiff. The accuracy analysis on this system was performed for all the algorithms described. Following this, a coupled spring‐pendulum example typical of real‐time testing is analysed with respect to both stability and accuracy issues. Finally, the results of representative numerical simulations and real‐time substructure tests, considering nonlinearities both in the numerical and the physical substructure, are explored. These tests were used to demonstrate how the LSRT algorithms can be used for substructuring tests with strongly nonlinear components.
Keywords: Earthquake, Nonlinear, Algorithms
Authors: Oreste S. Bursi; Zhen Wang; Chuanguo Jia; and Bin Wu
DOI: 10.1007/s00466-012-0800-0
Abstract: Real-time (RT) heterogeneous simulations define a class of hybrid numerical–experimental techniques based on dynamic substructuring and capable of simulating the non-linear response of an emulated mechanical system. With this objective in mind, we present two direct coupling algorithms endowed with subcycling, capable of ensuring the continuity of acceleration between non-overlapping subdomains. In greater detail, firstly we introduce monolithic Rosenbrock L-stable algorithms and, in view of the analysis of complex emulated systems, we recall a recent direct parallel algorithm. Secondly, we propose an improved parallel version of the progenitor algorithm together with its solution procedure. Consequently, in order to reduce drift, we introduce a mass-orthogonal velocity projection characterized by a non-negative energy dissipation. Moreover, both a convergence analysis on a SDoF test problem and simulations on single- and four-DoF systems are presented. Lastly, a novel test rig devised to perform nonlinear substructured RT tests is introduced and a few test results are presented.
Keywords: RTHS, Nonlinear, Algorithms, Experimental
Authors: Bin Wu; Zhen Wang; and Oreste S. Bursi
DOI: 10.1002/eqe.2296
Abstract: Real‐time hybrid simulation represents a powerful technique capable of evaluating the structural dynamic performance by combining the physical simulation of a complex and rate‐dependent portion of a structure with the numerical simulation of the remaining portion of the same structure. Initially, this paper shows how the stability of real‐time hybrid simulation with time delay depends both on compensation techniques and on time integration methods. In particular, even when time delay is exactly known, some combinations of numerical integration and displacement prediction schemes may reduce the response stability with conventional compensation methods and lead to unconditional instability in the worst cases. Therefore, to deal with the inaccuracy of prediction and the uncertainty of delay estimation, a nearly exact compensation scheme is proposed, in which the displacement is compensated by means of an upper bound delay and the desired displacement is picked out by an optimal process. Finally, the advantages of the proposed scheme over conventional delay compensation techniques are shown through numerical simulation and actual tests.
Keywords: RTHS, UQ
Authors: Zhen Wang; Bin Wu; Oreste S. Bursi; Guoshan Xu; and Yong Ding
DOI: 10.12989/sss.2014.14.6.1247
Abstract: Real-Time Hybrid Simulation (RTHS) is a novel approach conceived to evaluate dynamic responses of structures with parts of a structure physically tested and the remainder parts numerically modelled. In RTHS, delay estimation is often a precondition of compensation; nonetheless, system delay may vary during testing. Consequently, it is sometimes necessary to measure delay online. Along these lines, this paper proposes an online delay estimation method using least-squares algorithm based on a simplified physical system model, i.e., a pure delay multiplied by a gain reflecting amplitude errors of physical system control. Advantages and disadvantages of different delay estimation methods based on this simplified model are firstly discussed. Subsequently, it introduces the least-squares algorithm in order to render the estimator based on Taylor series more practical yet effective. As a result, relevant parameter choice results to be quite easy. Finally in order to verify performance of the proposed method, numerical simulations and RTHS with a buckling-restrained brace specimen are carried out. Relevant results show that the proposed technique is endowed with good convergence speed and accuracy, even when measurement noises and amplitude errors of actuator control are present.
Keywords: RTHS, Algorithms, Experimental
Authors: Oreste S. Bursi; Md S. Reza; Giuseppe Abbiati; and Fabrizio Paolacci
DOI: 10.1016/j.jlp.2014.11.004
Abstract: Assessment of seismic vulnerability of industrial petrochemical and oil & gas piping systems can be performed, beyond analytical tools, through experimental testing as well. Along this line, this paper describes an experimental test campaign carried out on a full-scale piping system in order to assess its seismic behaviour. In particular, a typical industrial piping system, containing several critical components, such as elbows, a bolted flange joint and a Tee joint, was tested under different levels of realistic earthquake loading. They corresponded to serviceability and ultimate limit states for support structures as suggested by modern performance-based earthquake engineering standards. The so called hybrid simulation techniques namely, pseudo-dynamic and real time testing with dynamic substructuring, were adopted to perform seismic tests. Experimental results displayed a favourable performance of the piping system and its components; they remained below their yielding, allowable stress and allowable strain limits without any leakage even at the Near Collapse Limit State condition for the support structure. Moreover, the favourable comparison between experimental and numerical results, proved the validity of the proposed hybrid techniques alternative to shaking table tests.
Keywords: Earthquake, Hybrid Simulation, Experimental
Authors: Guoshan Xu; Zhen Wang; Bin Wu; Oreste S. Bursi; Xiaojing Tan; Qingbo Yang; Long Wen; and Hongbin Jiang
DOI: 10.1002/tal.1354
Abstract: A novel horizontal and vertical wall‐to‐wall and wall‐to‐floor connection methods for precast box‐modularized structure with reinforced concrete shear walls (PBSRCSWs) are proposed in this paper. The entailing behavior of the proposed connections and the seismic performance of one full‐scale six‐story PBSRCSWs were experimentally studied by means of pseudodynamic substructure tests. In order to improve the relevant experimental accuracy, we presented and validated one versatile testing platform Hytest, combined with external displacement feedback control (EDFC; Hytest with EDFC). In greater detail, it was shown from the pseudodynamic substructure test results that the proposed Hytest with EDFC can effectively impose the desired displacements on the specimens rather than on the actuators. Moreover, both the horizontal and vertical wall‐to‐wall connections proposed for the PBSRCSWs exhibited a favorable behavior whilst the PBSRCSWs subjected to earthquake records showed an excellent seismic performance.
Keywords: Earthquake, Hybrid Simulation, Experimental
Authors: Zhu Mei; Bin Wu; Oreste S. Bursi; Ge Yang; and Zhaoran Wang
DOI: 10.1002/stc.2069
Abstract: Online model updating in hybrid simulation (HS) can represent an effective technique to reduce modeling errors of parts numerically simulated, that is, numerical substructures, especially when only a few critical components of a large system can be tested, that is, physical substructures. As a result, in an enhanced HS with online model updating, parameters of constitutive relationship can be identified based on experimental data provided by physical substructures and updated in numerical substructures. This paper proposes a novel method to identify constitutive parameters of concrete laws with unscented Kalman filter (UKF). In order to implement UKF, parts of the source codes of the OpenSEES software were modified to compute estimated measurements. Prior to experimental HS, a parametric study of UKF constitutive law parameters was conducted. As a result, the effectiveness of the UKF combined with OpenSEES was validated through numerical simulations, a monotonic loading test on a concrete column and real‐time HSs of a reinforced concrete frame run with both standard and model‐updating techniques based on UKF.
Keywords: Hybrid Simulation, Nonlinear, Model Updating, Large Scale, Experimental
Authors: Zhen Wang; Bin Wu; Guoshan Xu; and Oreste S. Bursi
DOI: 10.1002/stc.2076
Abstract: The equivalent force control (EFC ) algorithm is a hybrid seismic testing method based on both an implicit integration algorithm and force feedback control. As it performs the computation of the numerical substructure with a fixed sampling number and some evaluations are not necessary, the EFC method is believed to be time‐consuming for seismic testing of nonlinear systems with complicated numerical substructure model. In order to tackle this problem, the EFC method with varying sampling number (vEFC ) has been conceived. The analysis of the vEFC method has shown that 2 traditional pseudodynamic testing (PDT) variants on the basis of implicit time integration schemes and numerical iteration, that is, the IPDT1 method and the IPDT2 method, can be recovered from the vEFC method. Moreover, the advantages of the vEFC method, such as fast response rate and compensation for control errors and possible slippage, are demonstrated.
Keywords: Hybrid Simulation, Nonlinear, Algorithms
Authors: Ge Yang; Bin Wu; Ge Ou; Zhen Wang; and Shirley Dyke
DOI: 10.1016/j.advengsoft.2017.05.007
Abstract: Hybrid simulation has been demonstrated to be a powerful method to evaluate the system-level dynamic performance of structure. With the numerical substructure analyzed with finite element software and the difficult-to-model components tested with an experimental substructure, complex structures with sophisticated behaviors can readily be examined through a hybrid simulation. To coordinate and synchronize the substructures in hybrid simulation, software is required. In recent studies, model updating has been integrated into hybrid simulation to improve testing accuracy by updating the numerical model during the analysis. However, online model updating scheme requires some modifications in the typical hybrid simulation testing procedure, and this greater complexity is entailed in its implementation regarding the collaboration of identification algorithms with existing hybrid simulation software. To address this issue and broaden the utilization of hybrid simulation with model updating, an existing platform named HyTest originally for conventional hybrid simulation is extended for this purpose. This version of HyTest facilitates the online identification of material constitutive parameters using experimental measurements in its finite element based identification module. It also includes a data center with a uniform data transmission protocol to incorporate different substructures and modules. A numerical example is used to demonstrate the online identification of material parameters for concrete and steel models in a reinforced column, and to verify the accuracy of the identification module. Lastly the effectiveness of HyTest in conducting hybrid simulation with model updating is validated using actual hybrid tests on a steel frame.
Keywords: Hybrid Simulation, Model Updating, Algorithms, Experimental
Authors: Amin Maghareh; Shirley Dyke; Siamak Rabieniaharatbar; and Arun Prakash
DOI: 10.1002/eqe.2775
Abstract: Real-time hybrid simulation (RTHS) is an effective and versatile tool for the examination of complex structural systems with rate dependent behaviors. To meet the objectives of such a test, appropriate consideration must be given to the partitioning of the system into physical and computational portions (i.e., the configuration of the RTHS). Predictive stability and performance indicators (PSI and PPI) were initially established for use with only single degree-of-freedom systems. These indicators allow researchers to plan a RTHS, to quantitatively examine the impact of partitioning choices on stability and performance, and to assess the sensitivity of an RTHS configuration to de-synchronization at the interface. In this study, PSI is extended to any linear multi-degree-of-freedom (MDOF) system. The PSI is obtained analytically and it is independent of the transfer system and controller dynamics, providing a relatively easy and extremely useful method to examine many partitioning choices. A novel matrix method is adopted to convert a delay differential equation to a generalized eigenvalue problem using a set of vectorization mappings, and then to analytically solve the delay differential equations in a computationally efficient way. Through two illustrative examples, the PSI is demonstrated and validated. Validation of the MDOF PSI also includes comparisons to a MDOF dynamic model that includes realistic models of the hydraulic actuators and the control-structure interaction effects. Results demonstrate that the proposed PSI can be used as an effective design tool for conducting successful RTHS.
Keywords: Earthquake, RTHS, Transfer Systems
Authors: Amin Maghareh; Jacob P. Waldbjørn; Shirley J. Dyke; Arun Prakash; and Ali I. Ozdagli
DOI: 10.1002/eqe.2713
Abstract: Real-time hybrid simulation (RTHS) is a powerful cyber-physical technique that is a relatively cost-effective method to perform global/local system evaluation of structural systems. A major factor that determines the ability of an RTHS to represent true system-level behavior is the fidelity of the numerical substructure. While the use of higher-order models increases fidelity of the simulation, it also increases the demand for computational resources. Because RTHS is executed at real-time, in a conventional RTHS configuration, this increase in computational resources may limit the achievable sampling frequencies and/or introduce delays that can degrade its stability and performance. In this study, the Adaptive Multi-rate Interface rate-transitioning and compensation technique is developed to enable the use of more complex numerical models. Such a multirate RTHS is strictly executed at real-time, although it employs different time steps in the numerical and the physical substructures while including rate-transitioning to link the components appropriately. Typically, a higher-order numerical substructure model is solved at larger time intervals, and is coupled with a physical substructure that is driven at smaller time intervals for actuator control purposes. Through a series of simulations, the performance of the AMRI and several existing approaches for multi-rate RTHS is compared. It is noted that compared with existing methods, AMRI leads to a smaller error, especially at higher ratios of sampling frequency between the numerical and physical substructures and for input signals with highfrequency content. Further, it does not induce signal chattering at the coupling frequency. The effectiveness of AMRI is also verified experimentally.
Keywords: Earthquake, RTHS, Experimental
Authors: S.A.Vilsen; T.Sauder; A.J.Sørensen; and M.Føre
DOI: 10.1016/j.oceaneng.2018.10.042
Abstract: This paper presents a method for Real-Time Hybrid Model testing (ReaTHM testing) of ocean structures. ReaTHM testing is an extension to traditional hydrodynamic model-scale testing, where the system under study is partitioned into physical and numerical substructures. The physical and numerical subsystems are connected in real-time through a control system. Based on experience with various ReaTHM tests, a general method for ReaTHM testing of ocean structures has been proposed. An experimental case study was carried out to illustrate the proposed method. The study was conducted in a state-of-the-art hydrodynamic laboratory, where a physical cylindrical buoy was placed in a still-water basin. Horizontal mooring loads from a numerical mooring system, which were modelled using the nonlinear finite element software RIFLEX were actuated onto the physical substructure. System performance was verified through comparison with a physical horizontal mooring system consisting of physical springs.
Keywords: RTHS, Nonlinear, Experimental, Case Study
Authors: Eirill Bachmann Mehammer; Martin Føre; Thomas Sauder; Valentin Bruno Chabaud; and Thomas Parisini
DOI: 10.1088/1742-6596/1104/1/012008
Abstract: Offshore wind power research is a rapidly growing field, because of the present climate crisis and increasing focus on renewable energy. Model testing plays an important role in the risk and cost analysis associated with offshore wind turbines (OWTs). The real-time hybrid model testing concept (ReaTHM testing) solves important challenges related to model testing of OWTs, such as achieving an accurate modelling of the wind field, and the occurrence of scaling issues when modelling wind and waves simultaneously. However, ReaTHM test set-ups are generally sensitive to noise, signal loss and inaccuracies in sensor values. The present study is focused on the design and implementation of a state estimator able to accurately estimate the position and velocity of floating structures, while taking disturbances into account. By combining the information received from several different sensors with mathematical models, the estimator provides smooth and reliable position and velocity estimates for ReaTHM testing applications. The main objective of the present study is to develop a kinematic state space model that could represent the motion of any floating structure in six degrees of freedom (6-DOF). The kinematic model is implemented in MATLAB, and acceleration time series obtained with numerical simulations are used as inputs. The computed outputs agree with the corresponding simulated motions. A Kalman estimator based on the state space model is designed, implemented and tested against virtual data from the numerical model, with artificially added disturbances. Sensitivity analyses addressing the robustness towards noise, time delays, signal loss and uncertainties are performed to identify the limits of the estimator. The estimator is demonstrated to be robust to most types of disturbances. Further, the state estimator is tested against physical data from laboratory experiments. Good agreement between the physically measured and the estimated states is observed.
Keywords: Wind, Wave, RTHS
Authors: Teng Wu and Wei Song
DOI: 10.1016/j.jweia.2019.04.005
Abstract: As buildings are designed to be taller and more slender, they become lighter and more flexible with less inherent damping. If left uncontrolled, excessive wind-induced building response can cause serious safety and serviceability issues. Additional damping provided by adding an auxiliary damping system to the tall building is considered as one of the most cost-effective means to suppress the wind-induced response. Typically, the performance of these damping systems is evaluated experimentally with scaled damper and building models. However, the simplified small-scale dampers may not truly reflect the complex behavior of the full-scale damping systems. To realize the effective reduction of the wind-induced response of tall buildings, a real-time aerodynamics hybrid simulation (RTAHS) methodology that can offer improved response evaluation of a tall building integrated with an auxiliary damping system is introduced in this study. In this novel dynamic testing approach, the accurate evaluation of wind-induced tall building response is achieved by interacting an aeroelastic model of the tall building with the numerical model of the full-scale damper via interfacing actuators during the wind-tunnel tests. The feasibility and simulation accuracy of the proposed dynamic testing technique in the wind tunnel is numerically demonstrated by two case studies involving the wind-induced response reduction of a tall building equipped with both small-scale and full-scale damper properties.
Keywords: Wind, RTHS, Experimental, Case Study
Authors: Weihua Su; Wei Song; and Vincent Hill
DOI: 10.2514/6.2019-2032
Abstract: The concept of hybrid simulation and experiment for aeroelastic testing is introduced in this paper. In a hybrid simulation, a coupled aeroelastic system is “broken down” into an aerodynamic simulation subsystem and a structural vibration subsystem. The coupling between structural dynamics and aerodynamics is still maintained by the real-time communication between the two subsystems. As the vibration of the testing article (a wing member or a full aircraft) is actuated by actuators, a hybrid aeroelastic simulation/experiment can eliminate the sizing constraint of the conventional aeroelastic testing performed within a wind-tunnel. It also significantly saves the cost of the wind-tunnel testing, especially when a fatigue study is conducted. However, several critical technical problems need to be addressed in both the aerodynamic simulation and vibration testing to enable a hybrid simulation in the teal time. This paper will prove the concept of hybrid simulation/experiment and discuss some of the critical problems underlying the hybrid simulation/experiment.
Keywords: Wind, RTHS, Experimental
Authors: Saeid Hayati and Wei Song
DOI: 10.1061/(ASCE)EM.1943-7889.0001399
Abstract: Servo-hydraulic actuators exhibit frequency-dependent variations of amplitude and delay during real-time hybrid simulation (RTHS). Effective compensation techniques to overcome these variations is a crucial component for the successful implementation of RTHS. Most of the existing compensation techniques have demonstrated effective performance under excitations with relatively low frequency bandwidth. To further advance the servo-hydraulic compensation for broader frequency bandwidth, this paper presents the design and performance evaluation of an optimal discrete-time model-based feedforward controller under inputs with broader frequency bandwidth as high as 0–30 Hz. As a compensation technique has not been fully explored in RTHS, the model-based design of discrete-time domain compensation techniques introduces the new technical challenge of inverting nonminimum phase systems. This paper identifies this new challenge by providing detailed supporting derivation, and explains the use of a digital filtering technique—a finite impulse response (FIR) filter—to address this new challenge, and the development process of the proposed FIR compensator using different optimization schemes. Furthermore, this paper demonstrates the compensation performance of the proposed FIR compensator, both numerically and experimentally, under reference inputs with various bandwidths, including bandlimited white noises with frequency bandwidth as high as 0–30 Hz. For comparison purposes, several existing feedforward compensation techniques are also implemented and compared with the proposed FIR compensator. Based on this study, it is found that the proposed FIR compensator technique not only provides excellent compensation performance under various bandwidths, but also offers great flexibility in its formulation by varying the model order with desired compensation performance and computational demands.
Keywords: RTHS, Experimental
Authors: Saeid Hayati and Wei Song
DOI: 10.12989/sss.2017.20.4.483
Abstract: Real-Time Hybrid Simulation (RTHS) is a powerful and cost-effective dynamic experimental technique. To implement a stable and accurate RTHS, time delay present in the experiment loop needs to be compensated. This delay is mostly introduced by servo-hydraulic actuator dynamics and can be reduced by applying appropriate compensators. Existing compensators have demonstrated effective performance in achieving good tracking performance. Most of them have been focused on their application in cases where the structure under investigation is subjected to inputs with relatively low frequency bandwidth such as earthquake excitations. To advance RTHS as an attractive technique for other engineering applications with broader excitation frequency, a discrete-time feedforward compensator is developed herein via various optimization techniques to enhance the performance of RTHS. The proposed compensator is unique as a discrete-time, model-based feedforward compensator. The feedforward control is chosen because it can substantially improve the reference tracking performance and speed when the plant dynamics is well-understood and modeled. The discrete-time formulation enables the use of inherently stable digital filters for compensator development, and avoids the error induced by continuous-time to discrete-time conversion during the compensator implementation in digital computer. This paper discusses the technical challenges in designing a discrete-time compensator, and proposes several optimal solutions to resolve these challenges. The effectiveness of compensators obtained via these optimal solutions is demonstrated through both numerical and experimental studies. Then, the proposed compensators have been successfully applied to RTHS tests. By comparing these results to results obtained using several existing feedforward compensators, the proposed compensator demonstrates superior performance in both time delay and Root-Mean-Square (RMS) error.
Keywords: Earthquake, RTHS, Experimental
Authors: Xiaoyun Shao; Weichiang Pang; Chelsea Griffith; Ershad Ziaei; and John van de Lindt
DOI: 10.1002/eqe.2704
Abstract: Hybrid simulations of a full-scale soft-story woodframe building specimen with various retrofits were carried out as part of the Network for Earthquake Engineering Simulation Research project – NEES-Soft: seismic risk reduction for soft-story woodframe buildings. The test structure in the hybrid simulation was a three-story woodframe building that was divided into a numerical substructure of the first story with various retrofits and a full-scale physical substructure of the upper two stories. Four long-stroke actuators, two at the second floor and two at the roof diaphragm, were attached to the physical substructure to impose the simulated seismic responses including both translation and in-plane rotation. Challenges associated with this first implementation of a full-scale hybrid simulation on a woodframe building were identified. This paper presents the development and validation of a scalable and robust hybrid simulation controller for efficient test site deployment. The development consisted of three incremental validation phases ranging from small-scale, mid-scale, to full-scale tests conducted at three laboratories. Experimental setup, procedure, and results of each phase of the controller development are discussed, demonstrating the effectiveness and efficiency of the incremental controller development approach for large-scale hybrid simulation programs with complex test setup.
Keywords: Earthquake, Hybrid Simulation, Large Scale, Experimental
Authors: Justin Adam Murray; Mehrdad Sasani; and Xiaoyun Shao
DOI: 10.1016/j.engstruct.2015.09.018
Abstract: Hybrid simulations combine physical and analytical components into a single simulation to evaluate theresponse of a structure, often under seismic ground motion. This allows an experiment to be conducted inwhich structural components with complex response can be modeled experimentally and morewell-known components can be represented within an analytical model. The coordination softwareUI-SimCor, developed by the MUST-SIM NEES facility at the University of Illinois at Urbana–Champaign, is a hybrid simulation tool which performs the dynamic analysis and other software andhardware coordination tasks for hybrid simulations. In many hybrid simulations, including those thathave used UI-SimCor, analytical models with few effective degrees of freedom are typically used. In sim-ulations where system-level behaviors and the response of the analytical components are of importance,a more detailed analytical system is needed. This changeover to a more complex analytical system andincrease in general complexity of the hybrid simulation can cause various issues within the UI-SimCorframework. This study discusses the difficulties and issues that arise from having large and complex ana-lytical substructures in hybrid simulation, and the effective mitigation or solutions to those problems.
Keywords: Hybrid Simulation, Large Scale, Experimental
Authors: Yunbyeong Chae; Ramin Rabiee; Abdullah Dursun; and Chul-Young Kim
DOI: 10.1002/eqe.2994
Abstract: Servo‐hydraulic actuators have been widely used for experimental studies in engineering. They can be controlled in either displacement or force control mode depending on the purpose of a test. It is necessary to control the actuators in real time when the rate‐dependency effect of a test specimen needs to be accounted for under dynamic loads. Real‐time hybrid simulation (RTHS) and effective force testing (EFT) method, which can consider the rate‐dependency effect, have been known as viable alternatives to the shake table testing method. Due to the lack of knowledge in real‐time force control, however, the structures that can be tested with RTHS and EFT are fairly limited. For instance, satisfying the force boundary condition for axially stiff members is a challenging task in RTHS, while EFT has a difficulty to be implemented for nonlinear structures. In order to resolve these issues, this paper introduces new real‐time force control methods utilizing the adaptive time series (ATS) compensator and compliance springs. Unlike existing methods, the proposed force control methods do not require the structural modeling of a test structure, making it easy to be implemented especially for nonlinear structures. The force tracking performance of the proposed methods is evaluated for a small‐scale steel mass block system with a magneto‐rheological damper subjected to various target forces. Accuracy, time delay, and resonance response of these methods are discussed along with their force control performance for an axially stiff member. Overall, a satisfactory force tracking performance was observed by using the proposed force control methods.
Keywords: Earthquake, RTHS, Nonlinear, Experimental
Authors: Yunbyeong Chae; Jinhaeng Lee; Minseok Park; and Chul-Young Kim
DOI: 10.1002/eqe.3042
Abstract: It is well known that real‐time hybrid simulation (RTHS) is an effective and viable dynamic testing method. Numerous studies have been conducted for RTHS during the last 2 decades; however, the application of RTHS toward practical civil infrastructure is fairly limited. One of the major technical barriers preventing RTHS from being widely accepted in the testing community is the difficulty of accurate displacement control for axially stiff members. For such structures, a servo‐hydraulic actuator can generate a large force error due to the stiff oil column in the actuator even if there is a small axial displacement error. This difficulty significantly restricts the implementation of RTHS for structures such as columns, walls, bridge piers, and base isolators. Recently, a flexible loading frame system was developed, enabling a large‐capacity real‐time axial force application to axially stiff members. With the aid of the flexible loading frame system, this paper demonstrates an RTHS for a bridge structure with an experimental reinforced concrete pier, which is subjected to both horizontal and vertical ground motions. This type of RTHS has been a challenging task due to the lack of knowledge for satisfying the time‐varying axial force boundary condition, but the newly developed technology for real‐time force control and its incorporation into RTHS enabled a successful implementation of the RTHS for the reinforced concrete pier of this study.
Keywords: Earthquake, RTHS, Large Scale, Experimental
Authors: Yunbyeong Chae; Minseok Park; Chul-Young Kim; and Young Suk Park
DOI: 10.1016/j.engstruct.2016.11.065
Abstract: A great number of studies have been conducted to study the loading rate effect on the behavior of reinforced concrete (RC) structures. A majority of these studies, however, are focused on the component behavior of an RC specimen by imposing a predefined cyclic displacement history on the specimen without considering the interaction of the specimen with the entire structural system. In this study, the rate-dependency effect of an RC pier on the global response of a bridge is experimentally investigated using the slow and real-time hybrid simulations. The RC pier is used to support a two-span prestressed concrete girder bridge. The nonlinear response of the bridge under earthquake loads is accounted for by physically testing the RC pier in a laboratory, while the upper structural system of the bridge including the bridge deck and girders are analytically modeled. A dynamic servo-hydraulic actuator is connected to the top of the pier to transfer the inertial force of the bridge deck and girders to the pier. Due to the lack of knowledge in real-time force control, the axial load effect on the dynamic response of the RC pier is not considered in this study. Prior to conducting the hybrid simulations, predefined cyclic displacement tests are conducted for the bridge pier specimens with the same displacement history, but with different rates, in order to investigate any change in strength and energy dissipation capacity of the RC pier. Then, a series of slow and real-time hybrid simulations are conducted to investigate the rate-dependency effect on the seismic response of the bridge. The results from the predefined cyclic displacement tests and hybrid simulations are provided and discussed along with the observation from these tests.
Keywords: Earthquake, RTHS, Nonlinear, Experimental
Authors: Ying Lei; Huan Zhou; and Zhi-Lu Lai
DOI: 10.1111/mice.12217
Abstract: Real‐time structural identification and damage detection are necessary for on‐line structural damage detection and optimal structural vibration control during severe loadings. Frequently, structural damage can be reflected in the stiffness degradation of structural elements. In this article, a time‐domain three‐stage algorithm with computational efficiency is proposed for real‐time tracking the onsets, locations, and extents of abrupt stiffness degradations of structural elements using measurements of structural acceleration responses. Structural dynamic parameters before damage are recursively estimated in stage I. Then, the time instants and possible locations of degraded structural elements are detected by tracking the errors between the measured data and the corresponding estimated values in stage II. Finally, the exact locations and extents of stiffness degradations of structural elements are determined by solving simple constrained optimization problems in stage III. Both numerical examples and an experimental test are used to validate the proposed algorithm for real‐time tracking the abrupt stiffness degradations of structural elements in linear or nonlinear structures using measurements of structural acceleration responses polluted by noises.
Keywords: Earthquake, Nonlinear, Algorithms, Experimental
Authors: Amin Maghareh; Christian E. Silva; and Shirley J. Dyke
DOI: 10.1016/j.ymssp.2017.11.009
Abstract: Hydraulic actuators play a key role in experimental structural dynamics. In a previous study, a physics-based model for a servo-hydraulic actuator coupled with a nonlinear physical system was developed. Later, this dynamical model was transformed into controllable canonical form for position tracking control purposes. For this study, a nonlinear device is designed and fabricated to exhibit various nonlinear force-displacement profiles depending on the initial condition and the type of materials used as replaceable coupons. Using this nonlinear system, the controllable canonical dynamical model is experimentally validated for a servo-hydraulic actuator coupled with a nonlinear physical system.
Keywords: Nonlinear, Experimental
Authors: Ge Ou; Ali Irmak Ozdagli; Shirley J. Dyke; and Bin Wu
DOI: 10.1002/eqe.2479
Abstract: In this paper, we propose a new actuator control algorithm that achieves the design flexibility, robustness, and tracking accuracy to give real‐time hybrid‐simulation users the power to achieve highly accurate and robust actuator control. The robust integrated actuator control (RIAC) strategy integrates three key control components: loop shaping feedback control based on H ∞ optimization, a linear‐quadratic‐estimation block for minimizing noise effect, and a feed‐forward block that reduces small residual delay/lag. The combination of these components provides flexible controller design to accommodate setup limits while preserving the stability of the H ∞ algorithm. The efficacy of the proposed strategy is demonstrated through two illustrative case studies: one using large capacity but relatively slow actuator of 2500 kN and the second using a small‐scale fast actuator. Actuator tracking results in both cases demonstrate that the RIAC algorithm is effective and applicable for different setups. Real‐time hybrid‐simulation validation is implemented using a three‐DOF building frame equipped with a magneto‐rheological damper on both setups. Results using the two very different physical setups illustrate that RIAC is efficient and accurate.
Keywords: Earthquake, RTHS, Algorithms, Experimental, Case Study, Controller Design
Authors: Daniel Gomez; Shirley J. Dyke; and Amin Maghareh
DOI: 10.12989/sss.2015.15.3.913
Abstract: Hybrid simulation is increasingly being recognized as a powerful technique for laboratory testing. It offers the opportunity for global system evaluation of civil infrastructure systems subject to extreme dynamic loading, often with a significant reduction in time and cost. In this approach, a reference structure/system is partitioned into two or more substructures. The portion of the structural system designated as 'physical' or 'experimental' is tested in the laboratory, while other portions are replaced with a computational model. Many researchers have quite effectively used hybrid simulation (HS) and real-time hybrid simulation (RTHS) methods for examination and verification of existing and new design concepts and proposed structural systems or devices. This paper provides a detailed perspective of the enabling role that HS and RTHS methods have played in advancing the practice of earthquake engineering. Herein, our focus is on investigations related to earthquake engineering, those with CURATED data available in their entirety in the NEES Data Repository.
Keywords: Earthquake, Hybrid Simulation, RTHS, Experimental
Authors: Fangshu Lin; Amin Maghareh; Shirley J. Dyke; and Xilin Lu
DOI: 10.1016/j.engstruct.2015.07.040
Abstract: Real-time hybrid simulation (RTHS) is gaining acceptance as an efficient and cost-effective method for realistic structural evaluation. Advances in real-time computing and control methods have enabled research in the development of this novel methodology to progress rapidly. However, to explore effectiveness and accuracy, and thus build broader confidence in the use of this method as an alternative to shake table testing, there is a need to better understand and address the key features that determine the success of an RTHS. Here we discuss the design and analysis of a SDOF RTHS case study conducted in Purdue University’s Intelligent Infrastructure Systems Lab (IISL). We examine the key factors that determine the success, through configuration of the test using predictive indicators, design of an appropriately effective actuator controller, and a thorough comparison with shake table testing. The reference structure chosen for this case study is a single story, moment resisting frame structure. This particular specimen is of lab scale and well-known component properties, making it a suitable choice for such an investigation. However, noise, control–structure interaction and damping introduce numerous challenges typically faced in establishing an effective RTHS configuration. We investigate two key issues that lead to the design of a successful RTHS, specifically the partitioning between numerical and physical substructure for stability and performance, and the actuator motion control algorithm. Predictive indicators are demonstrated to be particularly helpful for properly configuring an RTHS experiment to meet a researcher’s specified objectives. Furthermore a direct comparison is conducted to examine the ability of RTHS to replicate a shake table test. The results demonstrate that with proper partitioning and actuator control design, successful RTHS can be implemented despite unfavorable transfer system properties.
Keywords: Earthquake, RTHS, Algorithms, Experimental, Education, Case Study, Transfer Systems
Authors: Anthony Friedman; Shirley J. Dyke, A.M.ASCE; Brian Phillips, A.M.ASCE; Ryan Ahn; Baiping Dong; Yunbyeong Chae; Nestor Castaneda; Zhaoshuo Jiang, A.M.ASCE; Jianqiu Zhang;
Youngjin Cha; Ali Irmak
Ozdagli; B. F. Spencer; James Ricles; Richard Christenson; Anil Agrawal, M.ASCE; and Richard Sause, M.ASCE
DOI: 10.1061/(ASCE)ST.1943-541X.0001093
Abstract: As magnetorheological (MR) control devices increase in scale for use in real-world civil engineering applications, sophisticated modeling and control techniques may be needed to exploit their unique characteristics. Here, a control algorithm that utilizes overdriving and backdriving current control to increase the efficacy of the control device is experimentally verified and evaluated at large scale. Real-time hybrid simulation (RTHS) is conducted to perform the verification experiments using the nees@Lehigh facility. The physical substructure of the RTHS is a 10-m tall planar steel frame equipped with a large-scale MR damper. Through RTHS, the test configuration is used to represent two code-compliant structures, and is evaluated under seismic excitation. The results from numerical simulation and RTHS are compared to verify the RTHS methodology. The global responses of the full system are used to assess the performance of each control algorithm. In each case, the reduction in peak and root mean square (RMS) responses (displacement, drift, acceleration, damper force, etc.) is examined. Beyond the verification tests, the robust performance of the damper controllers is also demonstrated using RTHS.
Keywords: Earthquake, RTHS, Large Scale, Algorithms, Experimental
Authors: Y-J Cha; A K Agrawal; and S J Dyke
DOI: 10.1088/0964-1726/22/1/015011
Abstract: This paper presents a detailed investigation on the robustness of large-scale 200 kN MR damper based semi-active control strategies in the presence of time delays in the control system. Although the effects of time delay on stability and performance degradation of an actively controlled system have been investigated extensively by many researchers, degradation in the performance of semi-active systems due to time delay has yet to be investigated. Since semi-active systems are inherently stable, instability problems due to time delay are unlikely to arise. This paper investigates the effects of time delay on the performance of a building with a large-scale MR damper, using numerical simulations of near- and far-field earthquakes. The MR damper is considered to be controlled by four different semi-active control algorithms, namely (i) clipped-optimal control (COC), (ii) decentralized output feedback polynomial control (DOFPC), (iii) Lyapunov control, and (iv) simple-passive control (SPC). It is observed that all controllers except for the COC are significantly robust with respect to time delay. On the other hand, the clipped-optimal controller should be integrated with a compensator to improve the performance in the presence of time delay.
Keywords: Earthquake, Large Scale, Algorithms, Experimental
Authors: Gregory Hackmann; Weijun Guo; Guirong Yan; Zhuoxiong Sun; Chenyang Lu; and Shirley Dyke
DOI: 10.1109/TPDS.2013.30
Abstract: Our deteriorating civil infrastructure faces the critical challenge of long-term structural health monitoring for damage detection and localization. In contrast to existing research that often separates the designs of wireless sensor networks and structural engineering algorithms, this paper proposes a cyber-physical codesign approach to structural health monitoring based on wireless sensor networks. Our approach closely integrates 1) flexibility-based damage localization methods that allow a tradeoff between the number of sensors and the resolution of damage localization, and 2) an energy-efficient, multilevel computing architecture specifically designed to leverage the multiresolution feature of the flexibility-based approach. The proposed approach has been implemented on the Intel Imote2 platform. Experiments on a simulated truss structure and a real full-scale truss structure demonstrate the system's efficacy in damage localization and energy efficiency.
Keywords: Algorithms, Experimental
Authors: Yili Qian; Ge Ou; Amin Maghareh; and Shirley J.Dyke
DOI: 10.1016/j.ymssp.2014.03.001
Abstract: In a typical Real-time Hybrid Simulation (RTHS) setup, servo-hydraulic actuators serve as interfaces between the computational and physical substructures. Time delay introduced by actuator dynamics and complex interaction between the actuators and the specimen has detrimental effects on the stability and accuracy of RTHS. Therefore, a good understanding of servo-hydraulic actuator dynamics is a prerequisite for controller design and computational simulation of RTHS. This paper presents an easy-to-use parametric identification procedure for RTHS users to obtain re-useable actuator parameters for a range of payloads. The critical parameters in a linearized servo-hydraulic actuator model are optimally obtained from genetic algorithms (GA) based on experimental data collected from various specimen mass/stiffness combinations loaded to the target actuator. The actuator parameters demonstrate convincing convergence trend in GA. A key feature of this parametric modeling procedure is its re-usability under different testing scenarios, including different specimen mechanical properties and actuator inner-loop control gains. The models match well with experimental results. The benefit of the proposed parametric identification procedure has been demonstrated by (1) designing an H∞ controller with the identified system parameters that significantly improves RTHS performance; and (2) establishing an analysis and computational simulation of a servo-hydraulic system that help researchers interpret system instability and improve design of experiments.
Keywords: Earthquake, RTHS, Algorithms, Experimental, Controller Design
Authors: Amin Maghareh; Shirley J. Dyke; Arun Prakash; and Jeffrey F. Rhoads
DOI: 10.12989/sss.2014.14.6.1221
Abstract: Real-time hybrid simulation (RTHS) is a promising cyber-physical technique used in the experimental evaluation of civil infrastructure systems subject to dynamic loading. In RTHS, the response of a structural system is simulated by partitioning it into physical and numerical substructures, and coupling at the interface is achieved by enforcing equilibrium and compatibility in real-time. The choice of partitioning parameters will influence the overall success of the experiment. In addition, due to the dynamics of the transfer system, communication and computation delays, the feedback force signals are dependent on the system state subject to delay. Thus, the transfer system dynamics must be accommodated by appropriate actuator controllers. In light of this, guidelines should be established to facilitate successful RTHS and clearly specify: (i) the minimum requirements of the transfer system control, (ii) the minimum required sampling frequency, and (iii) the most effective ways to stabilize an unstable simulation due to the limitations of the available transfer system. The objective of this paper is to establish a stability switch criterion due to systematic experimental errors. The RTHS stability switch criterion will provide a basis for the partitioning and design of successful RTHS.
Keywords: Earthquake, RTHS, Experimental, Transfer Systems
Authors: Amin Maghareh; Shirley J. Dyke; Arun Prakash; and Gregory B. Bunting
DOI: 10.1002/eqe.2448
Abstract: Real‐time hybrid simulation (RTHS) is increasingly being recognized as a powerful cyber‐physical technique that offers the opportunity for system evaluation of civil structures subject to extreme dynamic loading. Advances in this field are enabling researchers to evaluate new structural components/systems in cost‐effective and efficient ways, under more realistic conditions. For RTHS, performance metric clearly needs to be developed to predict and evaluate the accuracy of various partitioning choices while incorporating the dynamics of the transfer system, and computational/communication delays. In addition, because of the dynamics of the transfer system, communication delays, and computation delays, the RTHS equilibrium force at the interface between numerical and physical substructures is subject to phase discrepancy. Thus, the transfer system dynamics must be accommodated by appropriate actuator controllers. In this paper, a new performance indicator, predictive performance indicator (PPI), is proposed to assess the sensitivity of an RTHS configuration to any phase discrepancy resulting from transfer system dynamics and computational/communication delays. The predictive performance indicator provides a structural engineer with two sets of information as follows: (i) in the absence of a reference response, what is the level of fidelity of the RTHS response? and (ii) if needed, what partitioning adjustments can be made to effectively enhance the fidelity of the response? Moreover, along with the RTHS stability switch criterion, this performance metric may be used as an acceptance criteria for conducting single‐degree‐of‐freedom RTHS.
Keywords: Earthquake, RTHS, Experimental, Transfer Systems
Authors: Derek Slovenec, S.M.ASCE; Alireza Sarebanha, S.M.ASCE; Michael Pollino, M.ASCE; Gilberto Mosqueda, M.ASCE; and Bing Qu, M.ASCE
DOI: 10.1061/(ASCE)ST.1943-541X.0001814
Abstract:The use of a stiff rocking core (SRC) has been proposed as a seismic rehabilitation technique to mitigate soft-story response in low-rise to midrise steel concentrically braced frame (CBF) structures. This technique uses a stiff, elastic “spine” to provide corrective lateral forces at the onset of soft-story response but otherwise remains passive for the first mode vibration response. Yielding link element can also be incorporated in the SRC-to-structure connection to dissipate energy and reduce overall building drift. An experimental testing program was performed to investigate the fundamental behaviors of the SRC rehabilitation technique applied to two approximately 1/3-scale prototype CBFs representative of modern and older design practices. Hybrid testing methods were used to simulate building dynamics, the influence of gravity framing, and response of upper stories for a midrise prototype building. Each prototype frame was subjected to two seismic ground motions to evaluate cumulative damage followed by quasi-static cyclic testing to failure. The results from these tests indicate that the SRC is effective at mitigating soft-story response by vertically redistributing lateral demands throughout the structure.
Keywords: Earthquake, Hybrid Simulation, Large Scale, Experimental
Authors: Ellen M. Rathje; Clint Dawson; Jamie E. Padgett; Jean-Paul Pinelli; Dan Stanzione; Ashley Adair; Pedro Arduino; Scott J. Brandenberg; Tim Cockerill; Charlie Dey; Maria
Esteva;
Fred L. Haan
Jr.; Matthew Hanlon; Ahsan Kareem;
Laura Lowes; Stephen Mock; and Gilberto Mosqueda.
DOI: 10.1061/(ASCE)NH.1527-6996.0000246
Abstract: Natural hazards engineering plays an important role in minimizing the effects of natural hazards on society through the design of resilient and sustainable infrastructure. The DesignSafe cyberinfrastructure has been developed to enable and facilitate transformative research in natural hazards engineering, which necessarily spans across multiple disciplines and can take advantage of advancements in computation, experimentation, and data analysis. DesignSafe allows researchers to more effectively share and find data using cloud services, perform numerical simulations using high performance computing, and integrate diverse datasets so that researchers can make discoveries that were previously unattainable. This paper describes the design principles used in the cyberinfrastructure development process, introduces the main components of the DesignSafe cyberinfrastructure, and illustrates the use of the DesignSafe cyberinfrastructure in research in natural hazards engineering through various examples.
Keywords: Earthquake, Wind, Wave, Experimental
Authors: M. Javad Hashemi; Gilberto Mosqueda; Dimitrios G. Lignos; Ricardo A. Medina; and Eduardo Miranda
DOI: 10.1080/13632469.2015.1110066
Abstract: Hybrid simulation can provide significant advantages for large-scale experimental investigations of the seismic response of structures through collapse, particularly when considering cost and safety of conventional shake table tests. Hybrid simulation, however, has its own challenges and special attention must be paid to mitigate potential numerical and experimental errors that can propagate throughout the simulation. Several case studies are presented here to gain insight into the factors influencing the accuracy and stability of hybrid simulation from the linear-elastic response range through collapse. The hybrid simulations were conducted on a four-story two-bay moment frame with various substructuring configurations. Importantly, the structural system examined here was previously tested on a shake table with the same loading sequence, allowing for direct evaluation of the hybrid simulation results. The sources of error examined include: (1) computational stability in numerical substructure; (2) setup and installation of the physical specimen representing the experimental substructure; and (3) the accuracy of the selected substructuring technique that handles the boundary conditions and continuous exchange of data between the subassemblies. Recommendations are made regarding the effective mitigation of the various sources of errors. It is shown that by controlling errors, hybrid simulation can provide reliable results for collapse simulation by comparison to shake table testing.
Keywords: Earthquake, Hybrid Simulation, Large Scale, Experimental, Case Study
Authors:Maikol Del Carpio Ramos; Gilberto Mosqueda; and M. Javad Hashemi
DOI: 10.1061/(ASCE)ST.1943-541X.0001328
Abstract:The implementation of two series of hybrid simulations that aim to trace the system-level seismic response of a four-story steel moment frame building structure through collapse is presented. In the first series of tests, a half-scale 1½-bay by 1½-story physical substructure of a special steel moment-resisting frame is considered, while in the second series the physical substructure corresponds to the gravity framing system with a similar-sized specimen. An objective of these tests is to demonstrate the potential of hybrid simulation with substructuring as a cost-effective alternative to earthquake simulators for large-scale system-level testing of structural frame subassemblies. The performance of a recently developed substructuring technique and time-stepping integration method for hybrid simulation are evaluated when employed with large and complex numerical substructures exhibiting large levels of nonlinear response. The substructuring technique simplifies the experimental setup by reducing the number of required actuators while adequately approximating the boundary conditions including lateral displacements and axial loads on columns. The test method was found to be reliable with capabilities to provide insight into experimental behavior of structural subassemblies under realistic seismic loading and boundary conditions.
Keywords: Earthquake, Hybrid Simulation, Nonlinear, Large Scale, Experimental
Authors: Bahareh Forouzan; Dilshan SP Amarsinghe Baragamage; Koushyar Shaloudegi; Narutoshi Nakata; and Weiming Wu
DOI: 10.1177/1369433219857847
Abstract:A new hybrid simulation technique has been developed to assess the behavior of a structure under hydrodynamic loading. It integrates the computational fluid dynamics and structural hybrid simulation and couples the fluid loading and structural response at each simulation step. The conventional displacement-based and recently developed force-based hybrid simulation approaches are adopted in the structural analysis. The concept, procedure, and required components of the proposed hybrid simulation are introduced in this article. The proposed hybrid simulation has been numerically and physically tested in case of a coastal building impacted by a tsunami wave. It is demonstrated that the force error in the displacement-based approach is significantly larger than that in the force-based approach. The force-based approach allows for a more realistic and reliable structural assessment under tsunami loading.
Keywords: Wave, Hybrid Simulation, Large Scale, Experimental
Authors: Liang Huang; Cheng Chen; Tong Guo; and Menghui Chen
DOI: 10.1061/(ASCE)EM.1943-7889.0001550
Abstract:In a real-time hybrid simulation (RTHS), the actuator delay in experimental results might deviate from actual structural responses and even destabilize the real-time test. Although the assumption of a constant actuator delay helps simplify the stability analysis of RTHS, experimental results often show that the actuator delay varies throughout the test. However, research on the effect of time-varying delay on RTHS system stability is very limited. In this study, the Lyapunov-Krasovskii functional is introduced for the stability analysis of RTHS system. Two stability criteria are proposed for a linear system with a single constant delay and a time-varying delay. It is demonstrated that (1) the stable region of a time-varying delay system shrinks with the increase of the first derivative of time-varying delay; and (2) the stable region of the time-varying delay system is smaller than that of constant-time-delay system. Computational simulations were conducted for RTHS systems with a single degree of freedom to evaluate the proposed criteria. When the experimental specimen is an ideal elastic spring, the stability region of RTHS system with time-varying delay is shown to depend on the stiffness partition, structural natural period, and damping ratio. Significant differences in stability regions indicate that the time-varying characteristics of actuator delay should be considered for stability analysis of RTHS systems.
Keywords: Earthquake, RTHS, Experimental
Authors:Weijie Xu; Tong Guo; and Cheng Chen
DOI: 10.12989/sem.2017.62.5.631
Abstract: Accurate actuator tracking plays an important role in real-time hybrid simulation (RTHS) to ensure accurate and reliable experimental results. Frequency-domain evaluation index (FEI) interprets actuator tracking into amplitude and phase errors thus providing a promising tool for quantitative assessment of real-time hybrid simulation results. Previous applications of FEI successfully evaluated actuator tracking over the entire duration of the tests. In this study, FEI with moving window technique is explored to provide post-experiment localized actuator tracking assessment. Both moving window with and without overlap are investigated through computational simulations. The challenge is discussed for Fourier Transform to satisfy both time domain and frequency resolution for selected length of moving window. The required data window length for accuracy is shown to depend on the natural frequency and structural nonlinearity as well as the ground motion input for both moving windows with and without overlap. Moving window without overlap shows better computational efficiency and has potential for future online evaluation. Moving window with overlap however requires much more computational efforts and is more suitable for post-experiment evaluation. Existing RTHS data from Network Earthquake Engineering Simulation (NEES) is utilized to further demonstrate the effectiveness of the proposed approaches. It is demonstrated that with proper window size, FEI with moving window techniques enable accurate localized evaluation of actuator tracking for real-time hybrid simulation.
Keywords: Earthquake, RTHS, Nonlinear, Experimental
Authors: Samuel Richardson; Cheng Chen; Jose Valdovinos; Wenshen Pong; and Kai Chen
DOI: 10.1115/PVP2015-45057
Abstract: Laboratory experiments play a critical role in earthquake engineering research for seismic safety evaluation of civil engineering structures. Servo-hydraulic actuators play a vital role to maintain the compatibility on boundaries between the analytical and experimental substructures in a real-time hybrid simulation. Previous study has indicated that actuator delay could significantly affect the accuracy of real-time hybrid simulation involving viscous dampers. Identifying the amount of actuator delay therefore is critical for reliability assessment of experimental results to properly interpret the performance of viscous dampers for seismic hazard mitigation. In this study a frequency domain based approach is applied for real-time hybrid simulation of viscous dampers with the presence of actuator delay. Computational simulations are conducted to assess the accuracy of the approach for estimating the delay when the substructures develop nonlinear behavior for reliability interpretation of real-time hybrid simulation.
Keywords: Earthquake, RTHS, Nonlinear, Experimental
Authors: Cheng Chen; Weijie Xu; Tong Guo; and Kai Chen
DOI: 10.1007/s11803-017-0409-6
Abstract:Uncertainties in structure properties can result in different responses in hybrid simulations. Quantification of the effect of these uncertainties would enable researchers to estimate the variances of structural responses observed from experiments. This poses challenges for real-time hybrid simulation (RTHS) due to the existence of actuator delay. Polynomial chaos expansion (PCE) projects the model outputs on a basis of orthogonal stochastic polynomials to account for influences of model uncertainties. In this paper, PCE is utilized to evaluate effect of actuator delay on the maximum displacement from real-time hybrid simulation of a single degree of freedom (SDOF) structure when accounting for uncertainties in structural properties. The PCE is first applied for RTHS without delay to determine the order of PCE, the number of sample points as well as the method for coefficients calculation. The PCE is then applied to RTHS with actuator delay. The mean, variance and Sobol indices are compared and discussed to evaluate the effects of actuator delay on uncertainty quantification for RTHS. Results show that the mean and the variance of the maximum displacement increase linearly and exponentially with respect to actuator delay, respectively. Sensitivity analysis through Sobol indices also indicates the influence of the single random variable decreases while the coupling effect increases with the increase of actuator delay.
Keywords: Earthquake, RTHS, UQ, Experimental
Authors: David Ferry; Gregory Bunting; Amin Maghareh; Arun Prakash; Shirley Dyke; Kunal Agrawal; Chris Gill; and Chenyang Lu
DOI: 10.1145/2656045.2656067
Abstract: Real-time hybrid simulation (RTHS) is an important tool in the design and testing of civil and mechanical structures when engineers and scientists wish to understand the performance of an isolated component within the context of a larger structure. Performing full-scale physical experimentation with a large structure can be prohibitively expensive. Instead, a hybrid testing framework connects part of a physical structure within a closed loop (through sensors and actuators) to a numerical simulation of the rest of the structure. If we wish to understand the dynamic response of the combined structure, this testing must be done in real-time, which significantly restricts both the size of the simulation and the rate at which it can be conducted. Adding parallelism to the numerical simulation can enable both larger and higher frequency real-time simulations, potentially increasing both the accuracy and the control stability of the test. We present a proof-of-concept exploration of the execution of real-time hybrid simulations (an exemplar of a more general class of cyber-mechanical systems) with parallel computations. We execute large numerical simulations within tight timing constraints and provide a reasonable assurance of timeliness and usability. We detail the operation of our system, its design features, and show how parallel execution could enable qualitatively better experimentation within the discipline of structural engineering.
Keywords: Earthquake, Nonlinear, Parallel RT Execution, Experimental
Authors: Jing Li; Zheng Luo; David Ferry; Kunal Agrawal; Christopher Gill; and Chenyang Lu
DOI: 10.1007/s11241-014-9213-9
Abstract: As multicore processors become ever more prevalent, it is important for real-time programs to take advantage of intra-task parallelism in order to support computation-intensive applications with tight deadlines. In this paper, we consider the global earliest deadline first (GEDF) scheduling policy for task sets consisting of parallel tasks. Each task can be represented by a directed acyclic graph (DAG) where nodes represent computational work and edges represent dependences between nodes. In this model, we prove that GEDF provides a capacity augmentation bound of 4-2/m and a resource augmentation bound of 2-1/m. The capacity augmentation bound acts as a linear-time schedulability test since it guarantees that any task set with total utilization of at most m/(4-2m) where each task’s critical-path length is at most 1/(4-2/m) of its deadline is schedulable on m cores under GEDF. In addition, we present a pseudo-polynomial time fixed-point schedulability test for GEDF; this test uses a carry-in work calculation based on the proof for the capacity bound. Finally, we present and evaluate a prototype platform—called PGEDF—for scheduling parallel tasks using global earliest deadline first (GEDF). PGEDF is built by combining the GNU OpenMP runtime system and the LITMUSRT operating system. This platform allows programmers to write parallel OpenMP tasks and specify real-time parameters such as deadlines for tasks. We perform two kinds of experiments to evaluate the performance of GEDF for parallel tasks. (1) We run numerical simulations for DAG tasks. (2) We execute randomly generated tasks using PGEDF. Both sets of experiments indicate that GEDF performs surprisingly well and outperforms an existing scheduling techniques that involves task decomposition.
Keywords: RTHS, Parallel RT Execution, Experimental
Authors: Huimeng Zhou; David J. Wagg; and Mengning Li
DOI: 10.1002/stc.2018
Abstract: The equivalent force control method uses feedback control to replace numerical iteration and solve the nonlinear equation in a real‐time hybrid simulation via the implicit integration method. During the real‐time hybrid simulation, a time delay typically reduces the accuracy of the test results and can even make the system unstable. The outer‐loop controller of the equivalent force control method can eliminate the effect of a small time delay. However, when the actuator has a large delay, the accuracy of the test results is reduced. The adaptive forward prediction method offers a solution to this problem. Thus, in this paper, the adaptive polynomial‐based forward prediction algorithm is combined with equivalent force control to improve the test accuracy and stability. The new method is shown to give good stability properties for a specimen with nonlinear stiffness by analyzing the location of the poles of the discrete transfer system. Simulations with linear and nonlinear specimens are then presented to demonstrate the effectiveness of this method. Finally, experimental results with a linear stiffness specimen and a magneto‐rheological damper are used to demonstrate that this method has better accuracy than the equivalent force control method with nonadaptive delay compensation.
Keywords: Earthquake, RTHS, Nonlinear, Algorithms, Experimental, Transfer Systems
Authors: Elke Mergny; Thomas Gernay; Guillaume Drion; and Jean-Marc Franssen
DOI: 10.1108/JSFE-09-2018-0022
Abstract: Purpose – The purpose of this paper is to propose a new framework based on linear control system theory and the use of proportional (P) controller and proportional integral (PI) controller to address identified stability issues and control the time properties in hybrid fire testing. Design/methodology/approach – The paper approaches hybrid fire testing as a control problem. It establishes the state equation to give the general stability conditions. Then, it shows how P and PI controllers can be incorporated in the system to maintain stability. A virtual hybrid fire testing is performed on a 2D steel frame for validation and to compare the performance of the controllers. Findings – Control system theory provides an efficient framework for hybrid fire testing and rigorously formulate the stability conditions of the system. The use of a P-controller stabilises the process, but this controller is not suitable for continuous change of stiffness of the substructures. In contrast, a PI-controller handle the stiffness changes. The results of a virtual hybrid fire testing of a 2D steel frame shows that the PI-controller succeeds in reproducing the global behaviour of the frame, even if the surrounding structure is non-linear and subjected to fire. Originality/value – The paper provides a rigorous formulation of the general problem of hybrid fire testing and shows the interest of a PI controller to control the process under varying stiffness. This methodology is a step forward for hybrid fire testing because it allows capturing the global behaviour of a structure, including where the numerical substructure behaves nonlinearly and is subjected to fire.
Keywords: Fire, Nonlinear, Theory
Authors:RuiyangZhang; Brian M.Phillips; Pedro L.Fernández-Cabán; and Forrest J.Masters
DOI: 10.1016/j.engstruct.2019.05.042
Abstract: Traditionally, structural optimization is a numerical process; candidate designs are created and evaluated through numerical simulation (e.g., finite element analysis). However, when dealing with complex structures that are difficult to model numerically, large errors could exist between the numerical model and the physical structure. In this case, the optimization is less meaningful because the optimal results are associated with the numerical model instead of the physical structure. Experiments can be included in the optimization algorithm to represent complex structures or components. However, the time and cost limitations are prohibitive when iteratively constructing and evaluating complete structural systems. Real-time hybrid simulation (RTHS) is an efficient and cost-effective experimental tool that combines numerical simulation with experimental testing to capture the total structural performance. This paper proposes a framework for real-time hybrid optimization (RTHO); RTHS is used to evaluate the performance of candidate designs within the optimization process. The framework creates a cyber-physical optimization environment using RTHS, a modern experimental technique with roots in earthquake engineering. This paper outlines the framework for RTHO with accompanying proof-of-concept studies. In a preliminary study, the base isolation design of a two-story building was optimized for seismic protection. RTHO was further validated for the optimal selection of multiple semi-active control law parameters for an MR damper installed in the isolation layer of a five-story base-isolated building. Both cases used RTHS to evaluate the candidate designs and particle swarm optimization (PSO) to drive the optimization. RTHO is well-suited to evaluate nonlinear experimental substructures, in particular those that do not undergo permanent damage such as structural control devices. Structural damage, if of interest, can be modeled through the numerical component. This paper proposes and demonstrates the integration of state-of-the-art optimization algorithms with state-of-the-art experimental methods – a cyber-physical approach to structural optimization.
Keywords: Earthquake, RTHS, Nonlinear, Algorithms, Experimental
Authors: Michael L. Whiteman; Pedro L. Fernández Cabán; Brian M. Phillips; Forrest J. Masters; Jennifer A. Bridge; and Justin R. Davis
DOI: 10.1061/9780784481349.007
Abstract: This paper explores a cyber-physical systems (CPS) approach to optimize the design of rigid, low-rise structures subjected to wind loading. The approach combines the accuracy of physical wind tunnel testing with the ability to efficiently explore a solution space using numerical optimization algorithms. The approach is fully automated, with experiments executed in a boundary layer wind tunnel (BLWT), sensor feedback monitored by a computer, and actuators used to generate physical changes to a mechatronic structural model. The approach was demonstrated for a low-rise structure with a parapet wall of variable height. A non-stochastic optimization algorithm was implemented to search along the domain of parapet heights to minimize both positive and negative pressures on the roof a of a 1:18 length scale low-rise building model. Experiments were conducted at the University of Florida Experimental Facility (UFEF) of the National Science Foundation’s (NSF) Natural Hazard Engineering Research Infrastructure (NHERI) program.
Keywords: Wind, Algorithms, Experimental
Authors: Michael L.Whiteman; Brian M.Phillips; Pedro L.Fernández-Cabán; Forrest J.Masters; Jennifer A. Bridge; and Justin R.Davis
DOI: 10.1016/j.jweia.2017.11.013
Abstract: This paper explores the use of a cyber-physical systems (CPS) approach to optimize the design of rigid, low-rise structures subjected to wind loading, with the intent of producing a foundational method to study more complex structures through future research. The CPS approach combines the accuracy of physical wind tunnel testing with the ability to efficiently explore a search space using numerical optimization algorithms. The approach is fully automated, with experiments executed in a boundary layer wind tunnel (BLWT), sensor feedback monitored by a computer, and actuators used to bring about physical changes to a mechatronic structural model. Because the model is undergoing physical change as it approaches the optimal solution, this approach is given the name “loop-in-the-model” optimization. Proof-of-concept was demonstrated for a low-rise structure with a parapet wall of variable height. Parapet walls alter the location of the roof corner vortices, reducing suction loads on the windward facing roof corners and edges and setting up an interesting optimal design problem. In the BLWT, the parapet height was adjusted using servo-motors to achieve a particular design. Experiments were conducted at the University of Florida Experimental Facility (UFEF) of the National Science Foundation's (NSF) Natural Hazard Engineering Research Infrastructure (NHERI) program.
Keywords: Wind, Algorithms, Experimental
Authors: Gaston A. Fermandois
DOI: 10.1016/j.ymssp.2019.05.041
Abstract: Real-time hybrid simulation (RTHS) is an experimental testing technique widely used for performance evaluation of structural systems such as large buildings and bridges subjected to earthquake loading. While RTHS testing has demonstrated over the last 20 years to be an efficient and cost-effective alternative to shaking table tests, especially for large structural systems with rate-dependent behavior, accurate and stable results from this methodology are highly dependent on the test specimen, loading equipment, and controller design for dynamic compensation. This paper presents a study on the accuracy and stability of model-based compensation (MBC) approaches for the implementation of a real-time hybrid simulation benchmark problem. The controller architecture is based on feedforward compensator, designed for reference tracking, while a feedback regulator provides improved robustness for undesired disturbance and sensor noise. The results provide evidence of the improved performance of MBC controllers compared to benchmark results. Moreover, the MBC controllers surpass the benchmark controller in terms of robustness, when multiple partitioning cases and control plant uncertainty are considered in the numerical simulations.
Keywords: Earthquake, RTHS, UQ, Large Scale, Experimental, Controller Design, Benchmark
Authors: Giuseppe Abbiati; Igor Lanese; Enrico Cazzador; Oreste S. Bursi; and Alberto Pavese
DOI: 10.1002/stc.2419
Abstract: Hybrid simulation reproduces the experimental response of large‐ or even full‐scale structures subjected to a realistic excitation with reduced costs compared with shake table testing. A real‐time control system emulates the interaction between numerical substructures, which replace subparts having well‐established computational models, and physical substructures tested in the laboratory. In this context, state‐space modeling, which is quite popular in the community of automatic control, offers a computationally cheaper alternative to the finite‐element method for implementing nonlinear numerical substructures for fast‐time hybrid simulation, that is, with testing timescale close to one. This standpoint motivated the development of a computational framework based on partitioned time integration, which is well suited for hard real‐time implementations. Partitioned time integration, which relies on a dual assembly of substructures, enables coupling of state‐space equations discretized with heterogeneous time step sizes. In order to avoid actuators stopping at each simulation step, the physical substructure response is integrated with the same rate of control system, whereas a larger time step size is allowed on the numerical substructure compatibly with available computational resources. Fast‐time hybrid simulations of a two‐pier reinforced concrete bridge tested at the EUCENTRE Experimental Laboratory of Pavia, Italy, are presented as verification example.
Keywords: Earthquake, Hybrid Simulation, Nonlinear, Algorithms, Experimental
Authors: Oh-Sung Kwon; Ho-Kyung Kim; Un Yong Jeong; and You-Chan Hwang
DOI: 10.1061/9780784482247.022
Abstract: Due to the challenges in numerical simulation of wind-structure interaction, the dynamic response of long-span bridges or high-rise buildings subjected to wind loads has been primarily evaluated through wind tunnel tests. The wind-tunnel tests, especially aeroelastic tests, require calibration of springs, masses, and the damping properties of an experimental specimen which takes considerable time and efforts. In hybrid simulation, where a numerical model and a physical specimen are tightly integrated, a component that is difficult to be represented with a numerical model is represented experimentally, while the rest of the structural system is represented numerically. In this paper, designs of two configurations of experimental apparatus for real-time wind-tunnel hybrid simulation are presented: one for section model tests of bridge decks and another one for high-rise buildings. The experimental apparatus for section model tests, which consists of four linear motors, is for aeroelastic tests of section model of a long-span bridge. The experimental apparatus for buildings consists of two linear motors to test aeroelastic response of scaled high-rise building model. The rational on the selection of the design configurations is discussed which is followed by configuration of the experimental setup and a potential strategy for running real-time hybrid simulation.
Keywords: Wind, RTHS, Experimental
Authors: Bai Ping Dong; Richard Sause; and James M. Ricles
DOI: 10.4028/www.scientific.net/KEM.763.967
Abstract: Real-time hybrid earthquake simulations (RTHS) were performed on steel moment-resisting frame (MRF) structures with nonlinear viscous dampers. The test structures for the RTHS contain a moment-resisting frame (MRF), a frame with nonlinear viscous dampers (DBF), and a gravity load system with associated seismic mass and gravity loads. The MRFs have reduced beam section beam-to-column connections and are designed for 100%, 75%, and 60%, respectively, of the base shear strength required by ASCE 7-10. RTHS were performed to evaluate the seismic performance of these MRF structures. Two phases of RTHS were conducted: (Phase-1) the DBF is the experimental substructure in the laboratory; and (Phase-2) the DBF with the MRF is the experimental substructure. Results from the two phases of RTHS are evaluated. The evaluation shows that the RTHS provide a realistic and accurate simulation of the seismic response of the test structures. The evaluation also shows that steel MRF structures designed with reduced strength and with nonlinear viscous dampers can have excellent seismic performance.
Keywords: Earthquake, RTHS, Nonlinear, Experimental
Authors: Baiping Dong; Richard Sause; and James M. Ricles
DOI: 10.1002/eqe.2572
Abstract: This paper presents real-time hybrid earthquake simulation (RTHS) on a large-scale steel structure with nonlinear viscous dampers. The test structure includes a three-story, single-bay moment-resisting frame (MRF), a three-story, single-bay frame with a nonlinear viscous damper and associated bracing in each story (called damped braced frame (DBF)), and gravity load system with associated seismic mass and gravity loads. To achieve the accurate RTHS results presented in this paper, several factors were considered comprehensively: (1) different arrangements of substructures for the RTHS; (2) dynamic characteristics of the test setup; (3) accurate integration of the equations of motion; (4) continuous movement of the servo-controlled hydraulic actuators; (5) appropriate feedback signals to control the RTHS; and (6) adaptive compensation for potential control errors. Unlike most previous RTHS studies, where the actuator stroke was used as the feedback to control the RTHS, the present study uses the measured displacements of the experimental substructure as the feedback for the RTHS, to enable accurate displacements to be imposed on the experimental substructure. This improvement in approach was needed because of compliance and other dynamic characteristics of the test setup, which will be present in most large-scale RTHS. RTHS with ground motions at the design basis earthquake and maximum considered earthquake levels were successfully performed, resulting in significant nonlinear response of the test structure, which makes accurate RTHS more challenging. Two phases of RTHS were conducted: in the first phase, the DBF is the experimental substructure, and in the second phase, the DBF together with the MRF is the experimental substructure. The results from the two phases of RTHS are presented and compared with numerical simulation results. An evaluation of the results shows that the RTHS approach used in this study provides a realistic and accurate simulation of the seismic response of a large-scale structure with rate-dependent energy dissipating devices.
Keywords: Earthquake, RTHS, Nonlinear, Large Scale, Experimental
Authors: Yunbyeong Chae; James M. Ricles; and Richard Sause
DOI: 10.1002/eqe.2429
Abstract: A series of large-scale real-time hybrid simulations (RTHSs) are conducted on a 0.6-scale 3-story steel frame building with magneto-rheological (MR) dampers. The lateral force resisting system of the prototype building for the study consists of moment resisting frames and damped brace frames (DBFs). The experimental substructure for the RTHS is the DBF with the MR dampers, whereas the remaining structural components of the building including the moment resisting frame and gravity frames are modeled via a nonlinear analytical substructure. Performing RTHS with an experimental substructure that consists of the complete DBF enables the effects of member and connection component deformations on system and damper performance to be accurately accounted for. Data from these tests enable numerical simulation models to be calibrated, provide an understanding and validation of the in-situ performance of MR dampers, and a means of experimentally validating performance-based seismic design procedures for real structures. The details of the RTHS procedure are given, including the test setup, the integration algorithm, and actuator control. The results from a series of RTHS are presented that includes actuator control, damper behavior, and the structural response for different MR control laws. The use of the MR dampers is experimentally demonstrated to reduce the response of the structure to strong ground motions. Comparisons of the RTHS results are made with numerical simulations. Based on the results of the study, it is concluded that RTHS can be conducted on realistic structural systems with dampers to enable advancements in resilient earthquake resistant design to be achieved.
Keywords: Earthquake, RTHS, Nonlinear, Large Scale, Algorithms, Experimental
Authors: Ana Sauca; Thomas Gernay; Fabienne Robert; Nicola Tondini; and Jean-Marc Franssen
DOI: 10.1108/JSFE-01-2017-0017
Abstract: Purpose – The purpose of this paper is to propose a method for hybrid fire testing (HFT) which is unconditionally stable, ensures equilibrium and compatibility at the interface and captures the global behavior of the analyzed structure. HFT is a technique that allows assessing experimentally the fire performance of a structural element under real boundary conditions that capture the effect of the surrounding structure. Design/methodology/approach – The paper starts with the analysis of the method used in the few previous HFT. Based on the analytical study of a simple one degree-of-freedom elastic system, it is shown that this previous method is fundamentally unstable in certain configurations that cannot be easily predicted in advance. Therefore, a new method is introduced to overcome the stability problem. The method is applied in a virtual hybrid test on a 2D reinforced concrete beam part of a moment-resisting frame. Findings – It is shown through analytical developments and applicative examples that the stability of the method used in previous HFT depends on the stiffness ratio between the two substructures. The method is unstable when implemented in force control on a physical substructure that is less stiff than the surrounding structure. Conversely, the method is unstable when implemented in displacement control on a physical substructure stiffer than the remainder. In multi-degrees-of-freedom tests where the temperature will affect the stiffness of the elements, it is generally not possible to ensure continuous stability throughout the test using this former method. Therefore, a new method is proposed where the stability is not dependent on the stiffness ratio between the two substructures. Application of the new method in a virtual HFT proved to be stable, to ensure compatibility and equilibrium at the interface and to reproduce accurately the global structural behavior. Originality/value – The paper provides a method to perform hybrid fire tests which overcomes the stability problem lying in the former method. The efficiency of the new method is demonstrated in a virtual HFT with three degrees-of-freedom at the interface, the next step being its implementation in a real (laboratory) hybrid test.
Keywords: Fire
Authors: Narutoshi Nakata; Richard Erb; and Matthew Stehman
DOI: 10.1080/13632469.2017.1342296
Abstract: This paper presents a robust mixed force and displacement control strategy for testing of base isolation bearings in real-time hybrid simulation. The mixed-mode control is a critical experimental technique to impose accurate loading conditions on the base isolation bearings. The proposed mixed-mode control strategy consists of loop-shaping and proportional-integral-differential controllers. Following experimental validation, the mixed-mode control was demonstrated through a series of real-time hybrid simulation. The experimental results showed that the developed mixed-mode control enables accurate control of dynamic vertical force on the base isolation bearings during real-time hybrid simulation.
Keywords: Earthquake, RTHS, Experimental
Authors: Matthew Stehman and Narutoshi Nakata
DOI: 10.1080/13632469.2015.1104745
Abstract: This article considers the use of actuator compensation in real-time hybrid simulation (RTHS) containing experimental substructures with complex control-structure-interaction (CSI). The existence of CSI in shake table testing is derived using theoretical relations. An infinite-impulse-response (IIR) compensator is developed to compensate for the shake table time delay as well as the effects of CSI. The efficacy of the IIR compensator is verified through numerical and experimental investigations of substructure shake table testing completed at Johns Hopkins University. IIR compensation is not limited to substructure shake table testing, and the concept is applicable to any RTHS that suffers from complex CSI.
Keywords: Earthquake, RTHS, Theory, Experimental
Authors: Narutoshi Nakata and Matthew Stehman
DOI: 10.12989/sss.2014.14.6.1055
Abstract: Substructure shake table testing is a class of real-time hybrid simulation (RTHS). It combines shake table tests of substructures with real-time computational simulation of the remaining part of the structure to assess dynamic response of the entire structure. Unlike in the conventional hybrid simulation, substructure shake table testing imposes acceleration compatibilities at substructure boundaries. However, acceleration tracking of shake tables is extremely challenging, and it is not possible to produce perfect acceleration tracking without time delay. If responses of the experimental substructure have high correlation with ground accelerations, response errors are inevitably induced by the erroneous input acceleration. Feeding the erroneous responses into the RTHS procedure will deteriorate the simulation results. This study presents a set of techniques to enable reliable substructure shake table testing. The developed techniques include compensation techniques for errors induced by imperfect input acceleration of shake tables, model-based actuator delay compensation with state observer, and force correction to eliminate process and measurement noises. These techniques are experimentally investigated through RTHS using a uni-axial shake table and three-story steel frame structure at the Johns Hopkins University. The simulation results showed that substructure shake table testing with the developed compensation techniques provides an accurate and reliable means to simulate the dynamic responses of the entire structure under earthquake excitations.
Keywords: Earthquake, RTHS, Experimental
Authors: Stathis Bousias; Anastasios Sextos; Oh-Sung Kwon; Olympia Taskari; Amr Elnashai; Nikos Evangeliou; and Luigi Di Sarno
DOI: 10.1080/13632469.2017.1351406
Abstract: This paper presents hybrid simulations of a three-span R/C bridge among EU, US, and Canada. The tests involved partners located on both sides of the Atlantic with each one assigned a numerical or a physical module of the substructured bridge. Despite the network latency in linking remote sites located on the two sides of the Atlantic the intercontinental hybrid simulation was accomplished and repeated successfully, highlighting the efficiency, and repetitiveness of the approach. Adaptations, challenges, and limitations are discussed, focusing on the implications of network communication latency, the insensitivity of the sub-structuring arrangement, and the accuracy of the results obtained.
Keywords: Earthquake, Hybrid Simulation, Experimental
Authors: Pei-Ching Chen; Shiau-Ching Hsu; You-Jin Zhong; and Shiang-Jung Wang
DOI: 10.12989/sss.2019.23.1.091
Abstract: Adopting sloped rolling-type isolation devices underneath a raised floor system has been proved as one of the most effective approaches to mitigate seismic responses of the protected equipment installed above. However, pounding against surrounding walls or other obstructions may occur if such a base-isolated raised floor system is subjected to long-period excitation, leading to adverse effects or even more severe damage. In this study, real-time hybrid simulation (RTHS) is adopted to assess the control performance of a smart base-isolated raised floor system as it is an efficient and cost-effective experimental method. It is composed of multiple sloped rolling-type isolation devices, a rigid steel platen, four magnetorheological (MR) dampers, and protected high-tech equipment. One of the MR dampers is physically tested in the laboratory while the remainders are numerically simulated. In order to consider the effect of input excitation characteristics on the isolation performance, the smart base-isolated raised floor system is assumed to be located at the roof of a building and the ground level. Four control algorithms are designed for the MR dampers including passive-on, switching, modified switching, and fuzzy logic control. Six artificial spectrum-compatible input excitations and three slope angles of the isolation devices are considered in the RTHS. Experimental results demonstrate that the incorporation of semi-active control into a base-isolated raised floor system is effective and feasible in practice for high-tech industry.
Keywords: Earthquake, RTHS, Algorithms, Experimental
Authors: Pei-Ching Chen; Chin-Ta Lai; and Keh-Chyuan Tsai
DOI: 10.1002/stc.2015
Abstract: Shaking table testing has been regarded as one of the most straightforward experimental approaches to evaluate the seismic response of structures subjected to earthquake ground motions. Therefore, reproducing an acceleration time history accurately becomes crucial for shaking table testing. In this study, a control framework for uniaxial shaking tables is proposed which incorporates a feedback controller into a weighted command shaping controller. It implements through outer‐loop control in addition to the conventional existing proportional‐integral inner‐loop control. The model‐based command shaping controller which considers the control‐structure interaction can be designed to shape either displacement or acceleration references. The weightings for the shaped displacement and acceleration can be calculated by a linear interpolation algorithm which considers the dominant frequency of the desired acceleration time history as well as the correlation between the displacement and acceleration responses of the shaking table. Accordingly, the weighted combination of the shaped displacement and acceleration generates the control command to the shaking table. On the other hand, the feedback controller deals with the system uncertainty and modeling error. Loop‐shaping design method is adopted to synthesize the feedback controller. Finally, the control framework is verified by several shaking table tests with and without a flexible specimen. Experimental results demonstrate the performance and robustness of the proposed control framework for shaking table test systems.
Keywords: Earthquake, UQ, Large Scale, Algorithms, Experimental
Authors: Pei-Ching Chen; Chia-Ming Chang; Billie F. Spencer Jr.; and Keh-Chyuan Tsai
DOI: 10.1007/s10518-014-9681-2
Abstract: Model-based feedforward–feedback tracking control has been shown as one of the most effective methods for real-time hybrid simulation (RTHS). This approach assumes that the servo-hydraulic system is a linear time-invariant model. However, the servo-control closed-loop is intrinsically nonlinear and time-variant, particularly when one considers the nonlinear nature of typical experimental components (e.g., magnetorheological dampers). In this paper, an adaptive control scheme applying on a model-based feedforward–feedback controller is proposed to accommodate specimen nonlinearity and improve the tracking performance of the actuator, and thus, the accuracy of RTHS. This adaptive strategy is used to estimate the system parameters for the feedforward controller online during a test. The robust stability of this adaptive controller is provided by introducing Routh’s stability criteria and applying a parameter projection algorithm. The tracking performance of the proposed control scheme is analytically evaluated and experimentally investigated using a broadband displacement command, and the results indicates better tracking performance for the servo-hydraulic system can be attained. Subsequently, RTHS of a nine-story shear building controlled by a full-scale magnetorheological damper is conducted to verify the efficacy of the proposed control method. Experimental results are presented for the semi-actively controlled building subjected to two historical earthquakes. RTHS using the adaptive feedforward–feedback control scheme is demonstrated to be effective for structural performance assessment.
Keywords: Earthquake, RTHS, Nonlinear, Algorithms, Experimental
Authors: Robin E. Kim; Fernando Moreu; and Billie F. Spencer Jr.
DOI: 10.1061/(ASCE)ST.1943-541X.0001530
Abstract: Railroads carry approximately 40% of the ton-miles of the freight in the United States. On the average, a bridge occurs every 2.25 km (1.4 mi) of track, making them critical elements. The primary load on the railroad bridges is the train, resulting in numerous models being developed to understand the dynamic response of bridges under train loads. However, because the problem is time-dependent and coupled, developing adequate models is challenging. Most of the proposed models fail to provide a simple yet flexible representation of the train, bridge, and track. This paper proposes a new hybrid model that is effective for solving the track–bridge interaction problem under moving trains. The main approach is to couple the finite-element model of the bridge with a continuous beam model of the track using the assumed modes method. Both single-track and multitrack bridges are considered. The hybrid model is validated against field measurements for a double-track bridge. This model is then used to predict critical train speeds. The results demonstrate that the hybrid model provides an effective and fundamental tool for predicting bridge dynamics subject to moving trains. The flexible feature of the model will allow accommodating more sophisticated vehicle models and track irregularities.
Keywords:
Authors: Chia-Ming Chang; Thomas M. Frankie; Billie F. Spencer Jr.; and Daniel A. Kuchma
DOI: 10.1080/13632469.2014.962670
Abstract: This study proposes a high-precision positioning correction method for multiple degree-of-freedom loading units in hybrid simulation. These loading units can impose inaccurate displacements to the specimens due to the elastic deformation at the reaction wall or connections. To compensate for these displacement errors, an online correction method adjusts the displacement command by the difference between the target and achieved displacement. This correction method also accompanies an accurate 6DOF monitoring system to detect the displacement errors. Two examples of hybrid simulation tests are provided to demonstrate the precise displacements attained on the specimens through this control method.
Keywords: Earthquake, Hybrid Simulation, Large Scale, Experimental
Authors: Takehiko Asai; Chia-Ming Chang; and B. F. Spencer Jr.
DOI: 10.1061/(ASCE)EM.1943-7889.0000844
Abstract: Traditional passive base-isolation systems provide an effective means to mitigate the responses of seismically excited structures. A challenge for these systems can be found in accommodating the large base displacements during severe earthquakes. Recently, active base-isolation systems, combining actively controlled actuators with passive isolation bearings, have been shown experimentally to produce reduced base displacements, while maintaining similar responses of the superstructure obtained by the passive base-isolation systems. The active control devices used in hybrid isolation systems are typically driven by an external power source, which may not be available during severe seismic events. Another class of isolation systems is smart base isolation, in which semiactive control devices are used in place of their active counterparts. This control strategy has been proven effective against a wide range of seismic excitation; however, there has been limited effort to experimentally validate smart base-isolation systems. In this study, the focus is on experimentally investigating and verifying a smart baseisolation system using real-time hybrid simulation (RTHS), which provides a cost-effective means to conduct such experiments because only the portion of the structure that is poorly understood needs to be represented experimentally, while the reminder of the structure can be modeled using a computer. In this paper, a prototype magnetorheological damper is physically tested, while the isolated building concurrently is simulated numerically. A model-based compensation strategy is used to carry out high-precision RTHS. The performance of the semiactive control strategies is evaluated using RTHS, and the efficacy of the smart base-isolation system is demonstrated. This smart base-isolation system is found to reduce base displacements and floor accelerations in a manner comparable with the active isolation system without the need for large external power sources.
Keywords: Earthquake, RTHS, Large Scale, Experimental
Authors: Zaixian Chen; Xueyuan Yan; Hao Wang; Xingji Zhu; and Billie F. Spencer
DOI: 10.3390/su10082655
Abstract: Compatibility among substructures is an issue for hybrid simulation. Traditionally, the structure model is regarded as the idealized shear model. The equilibrium and compatibility of the axial and rotational direction at the substructure boundary are neglected. To improve the traditional boundary technique, this paper presents a novel substructure hybrid simulation boundary technique based on beam/column inflection points, which can effectively avoid the complex operation for realizing the bending moment at the boundary by using the features of the inflection point where the bending moment need not be simulated in the physical substructure. An axial displacement prediction technique and the equivalent force control method are used to realize the proposed method. The numerical simulation test scheme for the different boundary techniques was designed to consider three factors: (i) the different structural layers; (ii) the line stiffness ratio of the beam to column; and (iii) the peak acceleration. The simulation results for a variety of numerical tests show that the proposed technique shows better performance than the traditional technique, demonstrating its potential in improving HS test accuracy. Finally, the accuracy and feasibility of the proposed boundary technique is verified experimentally through the substructure hybrid simulation tests of a six-story steel frame model.
Keywords: Earthquake, Hybrid Simulation, Large Scale, Experimental
Authors: Xuguang Wang; Robin E. Kim; Oh-Sung Kwon, M.ASCE; In-Hwan Yeo; and Jae-Kwon Ahn
DOI: 10.1061/(ASCE)ST.1943-541X.0002436
Abstract: The continuous hybrid fire-simulation method proposed in this paper is a robust method that allows numerical models with a certain level of complexity to be used in a real-time hybrid fire simulation. Extrapolation and interpolation are used for continuously generating displacement commands during the simulation. The elastic deformation of the loading frame is compensated for during the continuous command generation. The stability issues relating to the stiffness of the loading system and the proposed error-compensation scheme are discussed in depth. A large-scale hybrid fire simulation was carried out to validate the proposed method. A steel moment-resisting frame with reduced beam section connections was selected for the validation test. One column of the selected structure was physically represented in the lab, and the rest of the structure was modeled numerically. The physical specimen was heated with a standard fire curve, with the temperature in the numerical model increasing following the numerical heat-transfer analysis result. A multiresolution numerical model was used as the numerical substructure. The test results confirmed the proposed method can accurately simulate the behavior of a structure subjected to high temperature and subsequent failure.
Keywords: Fire, RTHS, Large Scale
Authors: Christian E. Silva; Daniel Gomez; Amin Maghareh; Shirley J. Dyke and Billie F. Spencer Jr.
DOI: 10.1016/j.ymssp.2019.106381
Abstract: This paper presents the problem definition and guidelines for a benchmark control problem in real-time hybrid simulation for a seismically excited building, to appear in a Special Issue of Mechanical Systems and Signal Processing. Benchmark problems have been especially useful in enabling a community of researchers to leap forward on a given topic, distill the lessons learned, and identify the capabilities and limitations of various approaches. The focus here is on the design of an effective transfer system displacement tracking controller which is a commonly used approach for ensuring that interface conditions between numerical and experimental substructures are satisfied. In this study, a laboratory model of a three-story steel frame is considered as the reference structure. Realistic numerical models are developed and provided to represent the numerical and experimental substructures and the transfer system, which is comprised of hydraulic actuation, sensing instrumentation, and control implementation hardware. Experimental components are identified and provided as Simulink models, which are executed in real-time using Simulink Desktop Real-Time capability to enable realistic virtual real-time hybrid simulation. The task of each participant of the Special Issue is to design, evaluate, and report on their proposed controller approaches using the numerical models and computational codes provided. Such approaches will be assessed for robustness and performance using the provided tools. This benchmark problem is expected to further the understanding of the relative merits, as well as provide a clear basis for evaluating the performance of various control approaches and algorithms for RTHS. To illustrate some of the design challenges, a sample control strategy employing a proportional-integral (PI) controller is included, in addition to the built-in control loop of the transfer system.
Keywords: Earthquake, RTHS, Algorithms, Experimental, Transfer Systems, Controller Design, Benchmark
Authors: Yuting Ouyang; Weixing Shi; Jiazeng Shan; and Billie F. Spencer
DOI: 10.1016/j.ymssp.2019.05.042
Abstract: A backstepping adaptive control method is proposed for on-line estimation of unknown servo-hydraulic dynamics and the compensation of time-varying lags in real-time hybrid simulation tests. The response tracking problem becomes a critical challenge when realistic experimental conditions are taken into consideration, such as control-structure interaction effects and sensor measurement noise. Unlike a conventional time-lag compensator, the proposed adaptive controller generates a command trajectory for the actuated system according to adaptive laws. Besides bringing response tracking error to zeros, the estimation of a first-principle actuator dynamic model is also facilitated in the proposed approach. Lyapunov stability analysis is systematically presented for designing the adaptive control law. Illustratively, a three-story seismically excited structure with different control strategies is utilized to demonstrate the efficiency and robustness of the proposed controller. A benchmark problem is then utilized for the verification of controller’s advancement. Four simulation cases with different damping/mass conditions and four ground excitation scenarios are selected for the application. As stated, favorable tracking performance has been observed with a remarkable improvement in performance evaluation.
Keywords: Earthquake, RTHS, Experimental, Controller Design, Benchmark
Authors: Xizhan Ning; Zhen Wang; Huimeng Zhou; Bin Wu; Yong Ding and Bin Xu
DOI: 10.1016/j.ymssp.2019.05.038
Abstract: Real-time hybrid simulation (RTHS) is a practical, cost-effective, and versatile experimental technique to evaluate structural performance under dynamic excitation. The simulated structure is commonly split into a physically tested rate-dependent substructure (PS) and a numerically simulated substructure (NS). A transfer system such as a servo-hydraulic actuator is used to impose boundary conditions on the PS. Consequently, efficient actuator control is necessary to guarantee reliable simulation results. However, time delay and uncertainties exist due to the dynamics of the actuator, which adversely influence the accuracy and stability of RTHS. Therefore, an innovative robust actuator dynamics compensation method is proposed in this study comprising three components, namely a mixed sensitivity-based robust H∞ controller to stabilize the actuator–specimen dynamics, a polynomial extrapolation module to further cancel the actuator delay, and an adaptive filter for displacement reconstruction of the actuator–specimen system. A detailed design procedure of the proposed strategy is presented. The efficacy of the proposed strategy is validated through a series of virtual tests on the benchmark problem for RTHS. Results show that the proposed method exhibits excellent tracking performance and robustness. In particular, the maximum values of the calculated time delay (TD), root mean square of the tracking error (RMSE), and peak tracking error (PE) are 0 ms, 2.56%, and 2.12%, respectively, whereas the maximum values of the standard deviation of TD, RMSE, and PE are 0 ms, 0.25%, and 0.33%, respectively.
Keywords: Earthquake, RTHS, Experimental, Transfer Systems, Controller Design, Benchmark
Authors: Weijie Xu; Cheng Chen; Tong Guo; and Menghui Chen
DOI: 10.1016/j.ymssp.2019.05.039
Abstract: Actuator control plays an essential role to achieve stable and accurate real-time hybrid simulation (RTHS) results. Delay compensation is often used to minimize the desynchronization at the interface between numerical and experimental substructures. In this study, a new delay compensation method is proposed for RTHS, which integrates the inverse compensation method (IC) and frequency-domain evaluation index (FEI). Window technique is utilized to enable FEI for calculation of almost instantaneous time delay and the IC parameter is then adjusted accordingly for optimal compensation. The performance of this windowed FEI compensation (WFEI) is evaluated and compared with that of the IC and the adaptive inverse compensation (AIC) through computational simulations of a benchmark model with different initial estimates of time delay. It is demonstrated that the WFEI compensation not only provides accurate actuator control when initial estimated time delay deviates from actual values but also have good robustness under unpredicted uncertainties of the servo-hydraulic system.
Keywords: Earthquake, RTHS, UQ, Experimental, Benchmark
Authors: Amirali Najafi; and Billie F. Spencer Jr.
DOI: 10.1016/j.ymssp.2019.06.023
Abstract: The real-time hybrid simulation (RTHS) methodology is an experimental technique involving substructuring of a full-scale experiment into numerical and experimental partitions. It offers a cost-effective solution and is highly practical in confined laboratory settings. Successful implementation of RTHS is dependent on successful tracking control and robustness of the hybrid simulation loop. This paper addresses the benchmark problem in RTHS, which intends to assess available actuator tracking controllers and other advanced computational frameworks for successful RTHS implementation. Most existing control algorithms tend to instability when faced with challenges of plant uncertainty and nonlinearity. Stability has been at odds with excellent tracking, where controllers with rigorous tracking have had poor stability performance and robust controllers have had poor tracking performance. This paper introduces an Adaptive Model Reference Control (aMRC) method for displacement tracking of actuators, which offers an excellent tracking ability and maintains robustness under unmodeled dynamics and uncertainties. The proposed controller is composed of feedforward and feedback links, a reference model, and an adaptation law. The tracking and robustness performance of the proposed algorithm are evaluated through a numerical RTHS of the three-story steel frame building described in the benchmark problem statement. The benchmark problem defines different mass and damping configurations while partitioning the structure. Additionally, the experimental substructure is made uncertain by modeling several actuator and stiffness parameters probabilistically, per the benchmark problem. The performance of the proposed controller is compared to several commonly employed control techniques and assessed using the evaluation criteria described in the benchmark problem statement. The results show that the proposed aMRC algorithm tracks the desired reference signal well while maintaining robustness.
Keywords: RTHS, UQ, Nonlinear, Algorithms, Experimental, Controller Design, Benchmark
Authors: Huimeng Zhou; Dan Xu; Xiaoyun Shao; Xizhan Ning; and Tao Wang
DOI: 10.1016/j.ymssp.2019.106260
Abstract: During a real-time hybrid simulation (RTHS), inevitable time delay of actuators when responding to a command will reduce the accuracy of test results and sometimes even cause unstable testing. The inner-loop controller of an actuator is generally capable of eliminating the effects due to small time-delays. However, if a test specimen behaves nonlinearly, accuracy of RTHS results will be impaired. In addition to the uncertainty of test specimens and transfer system, measurement noises of the displacement and force sensors also require a robust external controller for RTHS. In this paper, a robust linear-quadratic-gaussian (LQG) controller with a Loop Transfer Recovery (LTR) procedure and a polynomial-based feedforward prediction (FP) algorithm is proposed to compensate the adverse effects due to time delay and uncertainties within the RTHS testing system. The stability and robustness of the proposed controller are analysed in the frequency domain using the Nyquist curve and the Bode diagrams. Numerical simulations are then carried out on the benchmark problem using both the proposed robust and the conventional LQG controllers and their performance is compared using the nine evaluation criteria. It is demonstrated that the robust LQG (RLQG) controller outperforms the conventional LQG controller in terms of compensating the parameter uncertainties in the testing system and achieving accurate RTHS results.
Keywords: RTHS, UQ, Nonlinear, Algorithms, Transfer Systems, Controller Design, Benchmark
Authors: Xiuyu S. Gao; and Shawn You
DOI: 10.1016/j.ymssp.2019.106261
Abstract: Real-time hybrid simulation is an advanced testing methodology to evaluate structural responses under realistic operating conditions. Typically, the real-time hybrid system uses actuation and control system to apply load and motion boundary conditions on the experimental substructure. The inherent system dynamics present phase lags, in addition to the communication delays, that both cause negative damping in the real-time hybrid system. In this study, the dynamic equation of motion is derived for a generalized multiple-degree-of-freedom hybrid system. The negative damping effect is quantified, which depends not only on the actuator motion control performance, but also more importantly on the partition between the numerical and experimental substructures (i.e. how the stiffness and mass are assumed in both substructures). It is demonstrated the worst-case hybrid substructure partition may have very narrow stability margin in its tolerance of any system delay. The proposed equation of motion gains system level understanding of any arbitrary hybrid substructure partition; thus allow both frequency domain system analysis and time domain evaluation. The benchmark problem is studied to validate the proposed equation of motion compared with the virtual testing method, both approaches show excellent correlation. These pre-testing assessments could establish quantitative predictive measures about the system stability limit and performance criteria. Thus they are very important in the early design stage of a feasible real-time hybrid implementation, help reduce the risks of unintended physical testing responses.
Keywords: Earthquake, RTHS, Experimental, Benchmark
Authors: Zhen Wang; Xizhan Ning; Guoshan Xu; Huimeng Zhou; and Bin Wu
DOI: 10.1016/j.ymssp.2019.106262
Abstract: Real-time hybrid simulation (RTHS) is an innovative and versatile technique for evaluating the dynamic responses of structural and mechanical systems. This technique separates the emulated system into numerical and physical substructures, which are analyzed by computers and loaded in laboratories, respectively. Ensuring the boundary conditions between the two substructures through a transfer system plays a significant role in obtaining reliable and accurate testing results. However, measurement noise and the delay between commands and responses due to the dynamic performance of the transfer system are inevitable in RTHS. To address these issues and to achieve outstanding tracking performance and excellent robustness, this paper proposes an adaptive Kalman-based noise filter and an adaptive two-stage delay compensation method. In particular, in the novel noise filter strategy, adaptive inverse compensation with parameters updated by the least squares method is adopted to accommodate the amplitude and phase errors induced by a traditional Kalman filter. In the proposed delay compensation method, classic polynomial extrapolation and an adaptive inverse strategy are employed for coarse and fine compensation, respectively. Virtual RTHS on a benchmark problem reveals the satisfactory tracking performance and robustness of the proposed methods. Comparisons with polynomial extrapolation and single-stage adaptive compensation indicate the superiority of the proposed two-stage delay compensation method.
Keywords: Earthquake, RTHS, Transfer Systems, Benchmark
Authors: Dan Xu; Huimeng Zhou; Xiaoyun Shao; and Tao Wang
DOI: 10.1016/j.ymssp.2019.106263
Abstract: Benchmark problem for real-time hybrid simulation (RTHS) is proposed to enable researchers assessing the robustness and performance of various tracking controllers in a uniform setting. In this paper, a controller combining the sliding mode controller (SMC) and an improved adaptive polynomial-based forward prediction (IAFP) algorithm is proposed. The SMC is adopted for its robustness to the uncertainties that may be experienced in an RTHS testing; while the IAFP is employed as a time delay compensator to stabilize RTHS with large time delay and reduce the time delay effects. Numerical simulations and physical experiments of the RTHS on a linear test specimen are conducted utilizing the program available through the benchmark problem. Time history responses obtained from RTHS are compared with those of the reference model and the nine evaluation criteria are computed, from which the robustness of the proposed controller and accurate RTHS results are demonstrated.
Keywords: Earthquake, RTHS, UQ, Algorithms, Experimental, Controller Design, Benchmark
Authors: Mohit Verma; and M.V. Sivaselvan
DOI: 10.1016/j.ymssp.2019.106343
Abstract: This paper presents an application of impedance matching to the benchmark control problem in real-time hybrid simulation (RTHS). Impedance matching is conceptually different from conventional approaches to designing controllers for RTHS. Rather than view the transfer system merely as a device to realize prescribed boundary conditions between the virtual and physical substructures, the controller is designed to match the impedance of transfer system as closely as possible to that of the virtual substructure. Some of the key features of impedance matching are—(i) it does not explicitly require a tracking controller, greatly simplifying the control design process, (ii) control design is decoupled from the physical substructure (demonstrated in this paper by introducing nonlinearity in the physical substructure), (iii) the controller is easy to evaluate and implement, (iv) performance is less sensitive to the choice of partitioning configuration compared to provided sample controller, and (v) exhibits robust stability. Overall, controllers designed based on impedance matching are found to result in stable and accurate RTHS.
Keywords: Earthquake, RTHS, Nonlinear, Experimental, Transfer Systems, Controller Design, Benchmark
Authors: Alejandro Palacio-Betancur; and Mariantonieta Gutierrez Soto
DOI: 10.1016/j.ymssp.2019.106345
Abstract: Real-time hybrid simulation (RTHS) is an interesting method for studying the performance of structures subjected to dynamic loading. RTHS decomposes a structure into partitioned physical and numerical sub-structures that are coupled together through actuation systems. The sub-structuring approach is particularly attractive for studying large-scale problems since it allows for setting up large-scale structures with thousands of degrees of freedom in numerical simulations while specific components can be studied experimentally. Due to the RTHS system dynamics, there is an inevitable time delay that affects accuracy and stability of the simulation. Several tracking control algorithms have been proposed to compensate time delay and improve the accuracy, however, robustness still presents challenges to obtain successful simulation results. In this paper, a Conditional Adaptive Time Series (CATS) compensator is proposed based on the principles of the Adaptive Time Series compensator (ATS) for a benchmark problem that consists of a three-story shear frame with one degree of freedom (DOF) in a virtual RTHS (vRTHS) that considers numerical and experimental models subjected to earthquake loading. A recursive least square (RLS) algorithm is adopted for the parameter estimation of the controller to reduce computational efforts in the simulation. The performance and robustness of a first-order CATS controller is evaluated for different partitioned cases. It is shown that an adaptive compensation strategy is an effective approach for RTHS based on nine performance criteria due to its simple implementation and accuracy.
Keywords: Earthquake, RTHS, Large Scale, Algorithms, Experimental, Benchmark
Authors: Junjie Tao; and Oya Mercan
DOI: 10.1016/j.ymssp.2019.106346
Abstract: Real-time hybrid simulation (RTHS) is a reliable and cost-effective testing technique to evaluate the dynamic response of a structural system, especially when the system includes rate-dependent components. Numerous studies suggest that the stability and accuracy of a RTHS are governed by the tracking errors between the calculated displacements and measured displacements during the test. In this study, frequency domain-based error indicators were designed to quantify the tracking errors in real-time. Consequently, an adaptive two degree-of-freedom phase-lead compensator was introduced to cancel out the identified tracking errors. Additionally, a proportional-integral -derivative controller was included as a supplement to further improve the tracking performance. The details of how to design the combined outer-loop controller were provided. A benchmark control problem in RTHS was used to assess the performance and robustness of the designed controller by carrying out a series of virtual RTHS (vRTHS), where different force excitations, partitioning configurations, and plant uncertainties were considered in MATLAB Simulink. Nine evaluation criteria were used to quantify the results of the vRTHS in this study. As a result, the proposed combined outer-loop controller was shown to be effective and robust to provide good stability and accuracy in RTHS.
Keywords: Earthquake, RTHS, UQ, Controller Design, Benchmark
Authors: Yingpeng Tian; Tao Wang; and Huimeng Zhou
DOI: 10.1504/IJLCPE.2020.108933
Abstract: Wind turbines are being used in increasingly complex working environments that generate coupled wind and earthquake effects. Areas with abundant onshore wind energy in China are concentrated in central and western earthquake-prone regions. Recent projects have tended to construct larger wind turbines to improve efficiency, but this generates more wind-induced vibration. Moreover, different threats are faced by a wind turbine at various stages. During construction, for example, vortex-induced resonance might result in a large lateral displacement of up to 1 meter, making the installation of blades difficult. Meanwhile, during service, the structure of a wind turbine can be damaged by strong gales and sometimes by earthquakes. The present study develops a tuned mass damper, which is designed to mitigate the lateral displacement introduced by vortex-induced resonance. The possibility of reducing the response to a gale and earthquake are then examined. Shaking-table substructure hybrid tests are conducted to verify the performance of the tuned mass damper for different external loads. The experimental results confirm the effectiveness in terms of suppressing vortex-induced resonance, while the mitigation of the response to wind and earthquakes is limited.
Keywords: Earthquake, Wind, Hybrid Simulation, Large Scale, Experimental
Authors: Connor Ligeikis; and Richard Christenson
DOI: 10.1504/IJLCPE.2020.108934
Abstract: While numerical simulations can be used to predict the dynamic performance of structural systems, there are some instances where the dynamical behavior and uncertainties of specific system components may be difficult to accurately model. In these instances, structural reliability assessments may be conducted by employing the cyber-physical real-time hybrid substructuring (RTHS) test method. In this approach, a numerical model of a larger structural system, incorporating uncertainty in specific parameters, is coupled with a physical test specimen of a system component to fully capture system-level dynamic interactions and facilitate uncertainty propagation. This paper specifically details a study performed to experimentally validate the previously proposed Adaptive Kriging-Hybrid Simulation (AK-HS) structural reliability method. The AK-HS method combines Kriging metamodeling, an adaptive learning algorithm, Monte Carlo simulation, and RTHS testing to iteratively estimate a structural systems probability of failure given random parameters in the numerical model. The method is validated with a series of bench-scale RTHS tests on a viscous damper connecting two adjacent 6-degree-of-freedom rigid body structures. The AK-HS method is shown to accurately predict probabilities of failure for systems with up to 24 random variables using a reasonable number of RTHS tests.
Keywords: Earthquake, RTHS, UQ, Algorithms, Experimental
Authors: Chinmoy Kolay; Safwan Al-Subaihawi; Thomas Marullo; James Ricles; and Spencer Quiel
DOI: 10.1504/IJLCPE.2020.108937
Abstract: The essence of real-time hybrid simulation (RTHS) is its ability to combine the benefits of physical testing and computational simulations and thereby efficiently simulate the dynamic response of a structure. The method is known to be accurate and more affordable compared to other dynamic testing techniques. However, the RTHS technique has primarily been applied to simulate seismic effects in structures. This paper successfully extends its application to wind response simulation of a 40-storey tall building outfitted with nonlinear fluid viscous dampers. In the RTHS, the building frame is modelled numerically, and the dampers are modelled physically. A series of RTHS is performed for both seismic and wind loadings. This paper presents the RTHS implementation procedure for multiple hazards, discusses the RTHS results and summarises the issues and challenges regarding the current implementation. The paper concludes with some remarks on the essence of RTHS in performance-based engineering considering multiple hazards.
Keywords: Earthquake, Wind, RTHS, Nonlinear, Experimental
Authors: Manuel Vega; Andreas Schellenberg; Humberto Caudana; and Gilberto Mosqueda
DOI: 10.1504/IJLCPE.2020.108939
Abstract: Large shake tables can provide extended capabilities to conduct large- and full-scale tests examining the seismic behavior of structural systems that cannot be readily obtained from reduced scale or quasi-static testing conditions. Assessing the behavior of large or complex structural systems introduces challenges such as high cost of full-scale specimens or capacity limitations of currently available shake tables. Some of these limitations may be overcome by employing the real-time hybrid shake table test method that requires only key subassemblies to be evaluated experimentally on the shake table while the remainder of the structure is modeled numerically. As a demonstration of the applicability of this testing method using a large shake table, a series of hybrid shake table tests were conducted on the UCSD Large High-Performance Outdoor Shake Table (LHPOST) with capabilities to test full scale structural models. A physical specimen was coupled with a numerical model using hybrid simulation techniques and shown to reproduce reliable results with adequate mitigation of experimental errors.
Keywords: Earthquake, RTHS, Large Scale, Experimental, Transfer Systems
Authors: Michael Harris; and Richard Christenson
DOI: 10.1504/IJLCPE.2020.108941
Abstract: In the field of structural dynamics, real-time hybrid simulation (RTHS) continues to receive increased interest from researchers conducting component testing incorporating system-level behaviour. Increased digital computing power has allowed advances in RTHS. However, limitations in RTHS will persist due to the effects of discrete errors caused by quantisation and corresponding numerical integration time step limitations, which can limit the bandwidth and nonlinearities of the system studied. In this paper, an analogue electronic computer is constructed to conduct RTHS of a modelled base-isolated structure with a physically tested viscous damping device. The analogue computer models a two-degree-of-freedom (2DOF) structure and solves the equations of motion required in RTHS testing. Results of the RTHS tests using the analogue computer are compared to RTHS tests implemented with a digital computer in order to validate the proposed analogue RTHS method. Further applications of RTHS testing with analogue computing including high-frequency dynamic testing are discussed.
Keywords: Earthquake, RTHS, Nonlinear, Experimental
Authors: Bahareh Forouzan; Koushyar Shaloudegi; and Narutoshi Nakata
DOI: 10.1504/IJLCPE.2020.108943
Abstract: Hybrid simulation is an advanced technique for dynamic analysis of structures, combining laboratory testing and numerical models. Many successful applications can be found in the studies for seismic analysis of structures. However, applications to the other hazards such as wind and tsunami have been very limited. One of the challenges is that the conventional hybrid simulation does not strictly ensure force equilibrium conditions at each time step, leaving unbalanced force error. In order to expand applications of hybrid simulation to various types of hazards, the unbalanced force has to be eliminated; it is because motion induced forces in aero and hydrodynamic loads have to be consistent with the structural deformation. This study proposes a force-based hybrid simulation to address the above challenge. The paper introduces a concept of force-based hybrid simulation and presents details of the force-based numerical integration algorithm. Following the description of the structural model and test setup, an experimental demonstration of the force-based hybrid simulation for a linear physical specimen is presented. Furthermore, numerical simulation using Bouc-Wen model is performed for an investigation of the applicability of the force-based hybrid simulation to nonlinear system.
Keywords: Wind, Wave, Hybrid Simulation, Nonlinear, Algorithms, Experimental
Authors: Jingzhe Wu; Ruiyang Zhang; and Brian Phillips
DOI: 10.1504/IJLCPE.2020.108944
Abstract: Seismic resilience provides a comprehensive assessment of the ability of a community to withstand and recover from earthquake disturbances. To support the design of seismic resilient structures, quantitative assessment of seismic resilience is needed and requires numerical simulations to be performed under a risk-based context. The associated large uncertainties can lead to large computational costs and limited accuracy in the numerical simulation, especially for structural systems with critical components having complex nonlinearity and rate-dependent behavior. To cope with such uncertainties and address simulation accuracy, a framework integrating real-time hybrid simulation is proposed to ensure the assessment accuracy of the seismic resilience of structures. With real-time hybrid simulation, modeling accuracy under wide range of design scenarios can be improved. To more efficiently develop fragility curves using the results of real-time hybrid simulation, experimental substructure component metamodeling is included through an online learning approach using long-short term memory neural networks. The proposed integration of real-time hybrid simulation and metamodeling in the fragility analysis to support resilience assessment is demonstrated through a proof-of-concept case study on the seismic retrofit of a 6-story building using inter-story isolation.
Keywords: Earthquake, RTHS, UQ, Nonlinear, Experimental, Case Study
Authors: Azin Ghaffary; Elif Ecem Bas; and Mohamed Moustafa
DOI: 10.1504/IJLCPE.2020.108942
Abstract: Wind tunnel testing is common practice for obtaining realistic design wind loads on specific buildings or optimizing geometric designs. Aeroelastic wind tunnel models are used to account for wind-structure interactions, but not as common as rigid models especially due to required physical simulation of reduced model stiffness and damping. Wind Real-Time Hybrid Simulation (wRTHS) is an evolving approach that can be utilized to improve aeroelastic modeling and current wind tunnel testing approaches. While RTHS has been extensively used for earthquake engineering applications, this paper aims at building on such knowledge and conduct foundational work to assess the performance of a typical RTHS setup for conducting future wRTHS. The main objective is to validate the performance of hardware, computational components, and the transfer system as envisioned for future use in wind tunnels. Four building structures with different breadth to height aspect ratios, one of them controlled by a tuned mass damper are used for this purpose. For sake of trial tests, wind loads form the Tokyo Polytechnic database are used to represent a hypothetical wind tunnel force that are applied to scaled numerical models of the structures in real time to calculate deformed shape of the building and reflect such deformation using hydraulic actuator. The different tests considered various existing RTHS methods but validated it for wind loading using two different computational platforms, namely Simulink and OpenSees. Given the different way of substructuring the equation of motion and frequency content of wind loads versus earthquakes, the test results indicate the validity and efficiency of the proposed hardware, software, and transfer system for future wRTHS.
Keywords: Earthquake, Wind, RTHS, Transfer Systems
Authors: Ge Ou; Arun Prakash; and Shirley Dyke
DOI: 10.1080/13632469.2015.1027018
Abstract: Stability in Real Time Hybrid Simulation (RTHS) has been shown to be largely affected by system dynamics and associated phase lags. This lag typically originates in the physical components and considerable research has been conducted to compensate for it. Within the computational component of RTHS, different time integration algorithms are employed to achieve a more stable and accurate solution, mostly focusing on dissipating the high frequency content in the model. However, in RTHS, an inherent computational delay exists in the force measurement due to the sequential nature of communication between the numerical and experimental sub- structures. In this article, it is demonstrated that this computational delay affects performance and stability of closed loop RTHS even when no other delays or phase lags are present. This finding is validated through theoretical derivation and simulation results. A modified Runge-Kutta (MRK) integration algorithm is proposed to reduce the effect of computational delay. The MRK integration involves a three-stage computation: (1) the pseudo response is calculated using the delayed force measurement; (2) feedback force from the physical component for the next step is predicted using the pseudo response; and (3) the corrected structural response is then computed using the predicted feedback force. Both analytical and simulation results confirm that the MRK integration scheme is stable and accurate for a wide range time steps and is robust with respect to modeling error and nonlinearity in the experimental substructure. A moment-resisting frame is used as the experimental substructure in different cases of RTHS to validate the MRK integration method. This approach can also be adapted to other existing numerical integration schemes by applying the proposed three-stage computation process approach.
Keywords: Earthquake, RTHS, Nonlinear, Theory, Algorithms, Experimental
Authors: Nestor Castaneda; Xiuyu Gao, A.M.ASCE; and Shirley J. Dyke, A.M.ASCE
DOI: 10.1061/(ASCE)CP.1943-5487.0000341
Abstract: Real-time hybrid simulation (RTHS) offers an economical and reliable methodology for testing integrated structural systems with rate-dependent behaviors. Within a RTHS implementation, critical components of the structural system under evaluation are physically tested, while more predictable components are replaced with computational models under a one-to-one timescale execution. As a result, RTHS implementations provide a more economical and versatile alternate approach to evaluating structural/rate-dependent systems under actual dynamic and inertial conditions, without the need for full-scale structural testing. One significant challenge in RTHS is the accurate representation of the physical complexities within the computational counterparts. For RTHS, the requirement for computational environments with reliable modeling and real-time execution capabilities is critical. Additionally, the need of a flexible environment for implementation and easy integration of such platforms with remaining RTHS components has also been established. An open-source computational platform, RT-Frame2D, for the RTHS of dynamically excited steel frame structures has been developed to satisfy these demands. The computational platform includes both adequate modeling capabilities for the nonlinear dynamic analysis of steel frame structures under real-time execution, and a versatile design to allow its efficient integration within a RTHS framework. Comparisons of RT-Frame2D modeling capabilities with those of a well-known simulation tool, in addition to challenging experimental implementations based on several RTHS scenarios, are performed herein to verify the accuracy, stability, and real-time execution performance of the proposed computational platform.
Keywords: Earthquake, RTHS, Nonlinear, Experimental
Authors: Xiuyu Gao; Nestor Castaneda; and Shirley J. Dyke
DOI: 10.1002/eqe.2246
Abstract: Real‐time hybrid simulation (RTHS) has increasingly been recognized as a powerful methodology to evaluate structural components and systems under realistic operating conditions. It is a cost effective approach compared with large scale shake table testing. Furthermore, it can maximally preserve rate dependency and nonlinear characteristics of physically tested (non)structural components. Although conceptually very attractive, challenges do exist that require comprehensive validation before RTHS should be employed to assess complicated physical phenomena. One of the most important issues that governs the stability and accuracy of an RTHS is the ability to achieve synchronization of boundary conditions between the computational and physical substructures. The objective of this study is to propose and validate an H∞ loop shaping design for actuator motion control in RTHS. Controller performance is evaluated in the laboratory using a worst‐case substructure proportioning scheme. A modular, one‐bay, one‐story steel moment resisting frame specimen is tested experimentally. Its deformation is kept within the linear range for ready comparison with the reference closed‐form solution. Both system analysis and experimental results show that the proposed H∞ strategy can significantly improve both the stability limit and test accuracy compared with several existing strategies. Another key feature of the proposed strategy is its robust performance in terms of unmodeled dynamics and uncertainties, which inevitably exist in any physical system. This feature is essential to enhance test quality for specimens with nonlinear dynamic behavior, thus ensuring the validity of the proposed approach for more complex RTHS implementations.
Keywords: Earthquake, RTHS, UQ, Nonlinear, Experimental, Controller Design
Authors: Young-Jin Cha, M.ASCE; Anil K. Agrawal; Anthony Friedman, M.ASCE; Brian Phillips; Ryan Ahn; Biping Dong; Shirley J. Dyke; Bill F. Spencer; James Ricles; and Richardson
Christenson
DOI: 10.1061/(ASCE)ST.1943-541X.0000982
Abstract: Magnetorheological dampers (MR) have the promising ability to mitigate seismic hazard for structures because of their adaptive energy dissipation characteristics and low power requirements that can be met using standby batteries. These attractive characterstics of advanced damping devices, such as MR dampers, are important for achieving the goals of performance-based infrastucture designs. This paper validates the performances of four semiactive control algorithms for the control of a large-scale realistic moment-resisting frame using a large-scale 200-kN MR damper. To conduct this test, a large-scale damper-braced steel frame was designed and fabricated. Four semiactive controllers, namely (1) passive on, (2) clipped optimal controller, (3) decentralized output feedback polynomial controller, and (4) Lyapunov stability based controller, were designed for this frame. Real-time hybrid simulations (RTHS) were carried out for these controllers using three recorded earthquakes. The comparative performance of these controllers was investigated using both RTHS and numerical simulations in terms of reductions in the maximum interstory drifts, displacements, absolute accelerations, and control forces, and comparisons between test and numerical results.
Keywords: Earthquake, RTHS, Large Scale, Algorithms, Controller Design
Authors: Xiuyu Gao, A.M.ASCE; Nestor Castaneda; and Shirley J. Dyke, M.ASCE
DOI: 10.1061/(ASCE)EM.1943-7889.0000696
Abstract: Real-time hybrid simulation (RTHS) has increasingly been recognized as a powerful methodology to evaluate structural components and systems under realistic operating conditions. The concept of RTHS combines the advantages of both numerical analysis and physical laboratory testing. Furthermore, the enforced real-time execution condition enables testing of rate-dependent components. One of the most important challenges in RTHS is to achieve synchronized boundary conditions between computational and physical substructures. The level of synchronization, i.e., actuators tracking performance, largely governs RTHS test stability and accuracy. The objective of this study is to propose and validate a generalized procedure for multiple-degree-of-freedom (MDOF) RTHS. A loop-shaping 𝐻∞ robust control design strategy is proposed to control the motion of the actuators. Validation experiments are performed successfully, including the challenges of multiple actuators dynamically coupled through a continuum steel moment resisting frame (MRF) specimen. The resulting framework is further utilized to evaluate the performance of a magnetorheological (MR) damper in its effectiveness to mitigate structural vibration when the structure is subjected to dynamic disturbances, e.g., earthquakes.
Keywords: Earthquake, RTHS, Experimental, Controller Design
Authors: X Gao; and S J Dyke
DOI: 10.1088/0964-1726/23/5/055008
Abstract: Most research in the structural engineering field uses either a simplified data-based model or a physics-based model to describe the dynamic behavior of servo-hydraulic actuators. In either way, the nominal model is typically used for modeling, analysis and control design. However, little effort has been directed to model uncertainties that are inherently associated with any physical system. A robust modeling approach is proposed in this study that can characterize both parametric and non-parametric uncertainties. The combination of this uncertainty with the nominal model provides a powerful tool to analyze the system performance and stability properties. Several control techniques are evaluated experimentally, and an H∞ robust control design is demonstrated to achieve the best performance as well as good robustness.
Keywords: Earthquake, RTHS, UQ, Experimental, Controller Design
Authors: Amin Maghareh; Shirley J. Dyke; Arun Prakash; and Jeffrey F. Rhoads
DOI: 10.12989/sss.2014.14.6.1221
Abstract: Real-time hybrid simulation (RTHS) is a promising cyber-physical technique used in the experimental evaluation of civil infrastructure systems subject to dynamic loading. In RTHS, the response of a structural system is simulated by partitioning it into physical and numerical substructures, and coupling at the interface is achieved by enforcing equilibrium and compatibility in real-time. The choice of partitioning parameters will influence the overall success of the experiment. In addition, due to the dynamics of the transfer system, communication and computation delays, the feedback force signals are dependent on the system state subject to delay. Thus, the transfer system dynamics must be accommodated by appropriate actuator controllers. In light of this, guidelines should be established to facilitate successful RTHS and clearly specify: (i) the minimum requirements of the transfer system control, (ii) the minimum required sampling frequency, and (iii) the most effective ways to stabilize an unstable simulation due to the limitations of the available transfer system. The objective of this paper is to establish a stability switch criterion due to systematic experimental errors. The RTHS stability switch criterion will provide a basis for the partitioning and design of successful RTHS.
Keywords: Earthquake, RTHS, Nonlinear, Experimental, Transfer Systems
Authors: Ali Irmak Ozdagli; Wang Xi; Gaby Ou; Bo Li; Shirley J. Dyke; Bin Wu; Jian Zhang; Ding Yong; Guoshan Xu; and Tao Wang
DOI: 10.1002/stc.2483
Abstract: Real‐time hybrid simulation (RTHS) has become a recognized methodology for isolating and testing complex, rate‐dependent structural components and devices to understand their behavior and to evaluate their ability to improve the performance of structures exposed to severe dynamic loading. Although RTHS is efficient in its utilization of equipment and space compared with conventional testing techniques, the laboratory resources may not always be available in a single testing facility to conduct large‐scale experiments. Consequently, distributed systems, capable of connecting multiple RTHS setups located at several geographically distributed facilities through appropriate information exchange, become desirable. This study presents a distributed RTHS (dRTHS) platform that enables the integration of geographically distributed physical and numerical components across the Internet. The essential capabilities needed to establish such a dRTHS platform are discussed, including the communication architecture, network components, and connection reliability. One significant challenge for conducting successful dRTHS is sustaining real‐time communication between test sites. To accommodate realistic network delays due to variations in the Internet service, a Smith predictor‐based delay compensation algorithm that includes a network time delay estimator is developed. A series of numerical and experimental studies is conducted to verify the platform and to quantify the impact of uncertainties present in a typical distributed system. Through an evaluation of the results, it is demonstrated that dRTHS is feasible for coupling laboratory capabilities and is a viable alternative to traditional testing techniques.
Keywords: Earthquake, RTHS, UQ, Large Scale, Algorithms, Experimental
Authors: J. Condori; A. Maghareh; J. Orr; H.-W. Li; H. Montoya; S. Dyke; C. Gill; and A. Prakash
DOI: 10.1007/s40799-020-00373-w
Abstract: Control is a critical element in many applications and research such as experimental testing in real-time. Linear approaches for control and estimation have been widely applied to real-time hybrid simulation (RTHS) techniques in tracking the physical domain (plant). However, nonlinearities and highly uncertainties of the plant impose challenges that must be properly addressed using nonlinear control procedures. In this study, a controller is developed for such an uncertain nonlinear system by integrating a robust control approach with a nonlinear Bayesian estimator. A sliding mode control methodology synthesizes the nonlinear control law to provide stability and accurate tracking performance, and a particle filter algorithm estimates the full state of the plant using measured signals such as displacement. The Hybrid Simulation Management (HSM) code is developed to implement dynamic systems and the improved nonlinear robust controller. The HSM is integrated in a novel run-time substrate named CyberMech, which is a platform developed to enhance the performance of real-time cyber-physical experiments that supports parallel execution. A set of experiments with a highly uncertain nonlinear dynamic system demonstrates that the combination of advanced control techniques and high performance computation enhances the quality of real-time experimentation and potentially expands RTHS techniques capabilities.
Keywords: RTHS, UQ, Nonlinear, Parallel RT Execution, Algorithms, Experimental, Controller Design
Authors: Amin Maghareh; Shirley J. Dyke; and Christian E. Silva
DOI: 10.1002/eqe.3260
Abstract: In a real‐time hybrid simulation, a transfer system is used to enforce the interface interaction between computational and physical substructures. A model‐based, multilayer nonlinear control system is developed to accommodate extensive performance variations and uncertainties in a physical substructure. The aim of this work is to extend the application of real‐time hybrid simulation to investigating failure, nonlinearity, and nonstationary behavior. This Self‐tuning Robust Control System (SRCSys) consists of two layers: robustness and adaptation. The robustness layer synthesizes a nonlinear control law such that the closed‐loop dynamics perform as intended under a broad range of parametric and nonparametric uncertainties. Sliding mode control is employed as the control scheme in this layer. Then, the adaptation layer reduces uncertainties at run time through slow and controlled learning of the control plant. The tracking performance of the SRCSys is evaluated in two experiments that have highly uncertain physical specimens.
Keywords: Earthquake, RTHS, UQ, Nonlinear, Experimental, Transfer Systems
Authors: Xu Huang; and Oh‐Sung Kwon
DOI: 10.1111/mice.12556
Abstract: Partitioned methods have been widely used in multiphysics and large‐scale structure‐media problems since they allow decomposition of a complex system into smaller subsystems. Although they have been considered to be superior to monolithic methods in terms of software reuse, difficulties still exist in the implementation process. This paper addresses these difficulties and proposes a new method to ease the coupling of the dynamic subsystems analyzed with different finite element codes. This is enabled by the development of a new staggered approach such that each involved program acts as a black box that is accessible only through model input and output, that is, displacements and forces, at the interface boundary. The accuracy and stability of the proposed method are numerically evaluated. A practical method to determine the maximum time step for stable solutions is also proposed. Two application examples are presented to verify the algorithm and demonstrate potential of the proposed method.
Keywords: Earthquake, Hybrid Simulation, Large Scale, Algorithms
Authors: Liang Huang; Tong Guo; Cheng Chen; and Menghui Chen
DOI: 10.1007/s11803-018-0477-2
Abstract: In real-time hybrid simulation (RTHS), it is difficult if not impossible to completely erase the error in restoring force due to actuator response delay using existing displacement-based compensation methods. This paper proposes a new force correction method based on online discrete tangent stiffness estimation (online DTSE) to provide accurate online estimation of the instantaneous stiffness of the physical substructure. Following the discrete curve parameter recognition theory, the online DTSE method estimates the instantaneous stiffness mainly through adaptively building a fuzzy segment with the latest measurements, constructing several strict bounding lines of the segment and calculating the slope of the strict bounding lines, which significantly improves the calculation efficiency and accuracy for the instantaneous stiffness estimation. The results of both computational simulation and real-time hybrid simulation show that: (1) the online DTSE method has high calculation efficiency, of which the relatively short computation time will not interrupt RTHS; and (2) the online DTSE method provides better estimation for the instantaneous stiffness, compared with other existing estimation methods. Due to the quick and accurate estimation of instantaneous stiffness, the online DTSE method therefore provides a promising technique to correct restoring forces in RTHS.
Keywords: Earthquake, RTHS, Experimental, Theory
Authors: Zili Zhang; Biswajit Basu; and Søren R.K. Nielsen
DOI: 10.1002/we.2281
Abstract: The present paper presents the real‐time hybrid simulation (RTHS) technique for multimegawatt wind turbine (WT) with various types of full‐scale tuned liquid dampers (TLDs). As an evolvement of the pseudodynamic testing technique, the RTHS is executed in real time, thus allowing accurate investigation of the interaction between the aeroelastic WT system and the rate‐dependent nonlinear TLD device. As the numerical substructure, the WT is simulated in the computer using a 13‐degree‐of‐freedom (13‐DOF) aeroelastic model. As the physical substructure, the full‐scale TLDs are manufactured and physically tested. They are synchronized with each other by real‐time controllers. Taking advantage of RTHS technique, 2‐ and 3‐MW WTs have both been simulated under various turbulent wind conditions. TLDs with different configurations have been extensively investigated, eg, various tuning ratios by varying the water level, TLD without and with damping screens (various mesh sizes of the screen considered), and TLD with flat and sloped bottoms. It is shown that a well‐designed TLD is very effective in damping lateral tower vibrations of WTs. Furthermore, RTHS results and results from a proposed theoretical model are compared. This study gives comprehensive guidelines for employing various types of TLDs in large WTs and indicates huge potentials of applying RTHS technique in the area of wind energy.
Keywords: Wind, RTHS, Experimental, Nonlinear, Large Scale, Theory
Authors: Selim Günay; Khalid Mosalam; and Shakhzod Takhirov
DOI: 10.1016/j.nucengdes.2015.05.020
Abstract: This paper presents extensive discussion on seismic qualification of substation equipment in conventional shake table tests and its comparison to real-time hybrid simulation (RTHS). The hybrid simulation technique is based on a sub-structuring idea where a portion of a test specimen with well-predicted performance can be replaced by its finite element model. The rest of the test specimen is experimentally studied as part of the coupled system, where the test object and the mathematical model are interacting with each other in real time. The real-time hybrid simulation technique has a strong potential of complementing and in some cases replacing seismic qualification testing. In addition to that, it has a strong potential as a comprehensive and reliable tool for IEEE693 development, where code provisions can be developed from parametric hybrid simulation studies of actual pieces of substation equipment which are otherwise difficult to model. As a typical example of successful application of hybrid simulation, a comprehensive study related to RTHS of electrical disconnect switches is discussed in the paper. First, the RTHS system developed for this purpose is described and the results of a RTHS test are compared with a benchmark conventional shaking table test as a validation of the system. Second, effect of the support structures of the disconnect switches on the global and local responses of different insulator types is evaluated using the results of a series of RTHS tests. Third, the paper investigates the advantages of using a sophisticated control approach for RTHS conducted on a long-stroke high-velocity shaking table. Finally, results of an application that uses the sophisticated control approach on a fully assembled phase of a disconnect switch are presented.
Keywords: Earthquake, RTHS, Experimental, Benchmark
Authors: Ho-Yeon Jung; In-Ho Kim; and Hyung-Jo Jung
DOI: 10.3390/s17112499
Abstract: Cable structure is a major component of long-span bridges, such as cable-stayed and suspension bridges, and it transfers the main loads of bridges to the pylons. As these cable structures are exposed to continuous external loads, such as vehicle and wind loads, vibration control and continuous monitoring of the cable are required. In this study, an electromagnetic (EM) damper was designed and fabricated for vibration control and monitoring of the cable structure. EM dampers, also called regenerative dampers, consist of permanent magnets and coils. The electromagnetic force due to the relative motion between the coil and the permanent magnet can be used to control the vibration of the structure. The electrical energy can be used as a power source for the monitoring system. The effects of the design parameters of the damper were numerically analyzed and the damper was fabricated. The characteristics of the damper were analyzed with various external load changes. Finally, the vibration-control and energy-harvesting performances of the cable structure were evaluated through a hybrid simulation. The vibration-control and energy-harvesting performances for various loads were analyzed and the applicability to the cable structure of the EM damper was evaluated.
Keywords: Wind, RTHS
Authors: Mostafa Nasiri; and Ali Safi
DOI: 10.1007/s12206-019-0301-6
Abstract: Real-time hybrid simulation evaluates the response of a structure in real time. In this study, a building with multi-story structure is divided into numerical and experimental substructures, and the vibration behavior of the experimental story is studied among the real-time simulation of the other stories. For applying the effect of static and inertial forces produced by the other stories to the experimental story, an electrohydraulic actuator and a shake table are used, respectively. The dynamics of the electrohydraulic actuator and the shake table can be estimated entirely by time delays, and these delays in the loop of simulation can reduce accuracy and cause system instability. Therefore, a delayed differential equation is used to determine the critical time delays depending on the system parameters. Results of simulation show the effect of non-dimensional parameters and time delays on the stability margin of hybrid simulation.
Keywords: Earthquake, RTHS, Experimental
Authors: Ruiyang Zhang, S.M.ASCE; and Brian M. Phillips, A.M.ASCE
DOI: 10.1061/(ASCE)EM.1943-7889.0001242
Abstract: Damping plays an important role in structural dynamics by absorbing energy and reducing structural responses. The inherent damping in a building ranges from approximately 2 to 10% critical damping in the first mode; even greater levels of damping are achieved when including supplemental damping devices such as viscous oil dampers. When creating laboratory scale structures, it is difficult to achieve the target level of damping in the specimen. Solutions such as adding discrete damping devices are costly, while solutions such as adding foam or other dissipative materials may add undesired nonlinear behavior or increase the stiffness. This paper proposes a novel technique to introduce artificial damping to a dynamic specimen through shake table control. Artificial damping (AD) is introduced by designing a feedforward (FF) shake table controller that compensates for both shake table dynamics and achieves target specimen performance; that is, with larger damping than the original specimen. The performance of the proposed artificial damping by FF (AD-FF) is investigated for both traditional shake table testing and shake table real-time hybrid simulation (RTHS) through a uniaxial shake table and a two-story shear building specimen with very low damping. The target level of structural damping is accurately realized through the proposed AD-FF in both traditional shake table testing and RTHS. Moreover, damping can be introduced to specific modes of the structure, a feature that cannot be realized by using physical damping devices. In RTHS, the proposed AD-FF gives researches the ability to increase stability without changing the dominant structural response by adding damping to higher modes, even if they appear in the specimen.
Keywords: Earthquake, RTHS, Controller Design
Authors: Thomas Börner; and Mohammad-Reza Alam
DOI: 10.1016/j.rser.2014.11.063
Abstract: Accurate modeling of ocean wave energy converters is limited mainly due to the reciprocating nature of the exciting force and consequent complications, particularly in the fluid domain. Direct simulation is usually computationally expensive, and experiments are constrained by scaling rules that cannot be satisfied simultaneously, and of course, by the costs. Many modeling problems, including several in ocean wave energy, can be divided into sub-domains that for each, one modeling scheme (e.g. numerical simulation or experiment) is practical and preferred. The idea behind hybrid simulation is to solve each sub-domain using the preferred method, while sub-domains communicate with each other at their common boundaries via sensors and actuators, with the prime objective of solving the main problem as a whole. We are particularly interested in the set of problems in which the subdomains are strongly coupled and hence significantly influence each other. The challenge is when one of the subproblems is to be modeled experimentally and therefore as a result the entire hybrid simulation modeling has to be carried out in real time. We review here the background and details of the real time hybrid simulation scheme with the specific focus on the modeling of ocean wave energy devices. We elaborate major challenges via a case study of a newly proposed seabed mounted pressure-differential wave energy converter called “Wave Carpet”. We find the optimum parameters of the power takeoff units as well as their optimal positioning in order to achieve the highest overall efficiency of the Wave Carpet.
Keywords: Wave, RTHS, Experimental, Case Study
Authors: Georgios Giotis; Oh-Sung Kwon, Ph.D., P.Eng., M.ASCE; and Shamim A. Sheikh, Ph.D., P.Eng., M.ASCE
DOI: 10.1061/(ASCE)ST.1943-541X.0002492
Abstract: In this study, a novel method is proposed which allows for testing facilities to run hybrid simulations when the number of actuators is less than the number of the available controlled degrees of freedom. The method is based on coupling of a surrogate numerical model with a physical specimen such that the numerical model can supplement the response of a degree of freedom (DOF) that cannot be obtained from the physical specimen. This paper presents the analytical study and the theoretical framework of the proposed methodology. Additionally, a parametric study is conducted for defining the method’s applicability to various frame elements whose structural characteristics represent common frame elements. The proposed methodology of this paper is numerically verified by performing the seismic performance assessment of a typical 3-story moment resisting frame (MRF). This article concludes with the applicability figures of the proposed simulation method and the summary of the parameters that influence the applicability of the simulation method.
Keywords: Earthquake, Hybrid Simulation, Theory, Experimental
Authors: Mehrdad Memari, A.M.ASCE; Xuguang Wang; Hussam Mahmoud, M.ASCE; and Oh-Sung Kwon, M.ASCE
DOI: 10.1061/(ASCE)ST.1943-541X.0002466
Abstract: Various studies have demonstrated the effectiveness of employing different fire protection strategies in reducing damage and losses associated with fire events in conventional buildings. However, studies geared toward understanding structural vulnerability due to fire following an earthquake, as a result of failure of the fire protection systems in a seismic event, are scarce. This study investigated the fire performance of a steel structure in two different scenarios: without a prior earthquake event, and with residual deformation from an earthquake event. To understand the fire performance of a structure that has been subjected to an earthquake, three different levels of seismic intensities were considered, represented by interstory drift ratios. To realistically simulate the structural behavior when subjected to elevated temperature, a hybrid fire simulation method was adopted in which a column was modeled physically and subjected to temperature and mechanical loads, whereas the remainder of the structure was modeled numerically. Due to laboratory constraints, a small-scale structure was used to illustrate the developed framework and demonstrate the potential effect of an earthquake on fire performance of a building. The test results showed that smaller axial deformation but larger force developed in the physical column when it was not subjected to an interstory drift prior to the fire event. On the other hand, columns with higher levels of residual interstory drift experienced larger vertical deformation and smaller axial force, and failed earlier than those with lower interstory drift. Based on the preliminary findings from this study, further investigations are recommended to quantify the effect of interstory drifts from seismic events on fire vulnerability of various types and configurations of structural steel systems. Full-scale hybrid simulations can serve as a valuable tool to gain insight into the behavior of these various systems.
Keywords: Earthquake, Fire, Hybrid Simulation, Large Scale, Theory, Algorithms, Experimental
Authors: Xu Huang; and Oh-Sung Kwon
DOI: 10.1080/13632469.2018.1423585
Abstract: This paper describes a generalized distributed simulation framework that has been developed at the University of Toronto. The proposed framework is characterized by the ability to integrate diverse numerical integration and substructure modules and experimental specimens. This feature is enabled by a standardized data-exchange format and a communication protocol through which any potential integration or substructure modules can communicate with each other. The data-exchange format is designed with the information required for various simulation purposes such as real-time simulation, hybrid simulation with thermal load, etc. Current development of the simulation framework is presented through several application examples, which are rarely seen from previous simulations.
Keywords: Earthquake, Hybrid Simulation, Nonlinear, Experimental
Authors: Hussam N. Mahmoud, A.M.ASCE; Amr S. Elnashai, M.ASCE; Billie F. Spencer Jr., F.ASCE; Oh-Sung Kwon, M.ASCE; and David J. Bennier
DOI: 10.1061/(ASCE)ST.1943-541X.0000721
Abstract: The behavior of semirigid partial-strength connections has been investigated through either experimental component testing or detailed three-dimensional (3D) finite-element (FE) models of beam-column subassemblies. Previous experiments on semirigid partial-strength connections were conducted under idealized loads and boundary conditions, which do not represent real situations. In addition, the developed 3D FE models are computationally expensive and have primarily been used under monotonic loadings. Evaluating the full potential of any connection requires a system-level investigation, whereby the effect of the local behavior of the connection on the global response of the structural system is considered. Moreover, the connection should be tested under realistic load and boundary conditions and/or analyzed using an accurate yet computationally affordable analytical model. This paper represents a new system-level hybrid simulation application aimed at investigating the seismic performance of semirigid partial-strength steel frames with top and seat angles with double web-angle connections. The analytical component of the simulation comprises a detailed two-dimensional nonlinear FE model. The experimental component of the simulation consists of a full-scale beam-column subassembly with loading and boundary conditions that are in full interaction with the rest of the frame. The paper provides an overview of the hybrid simulation application and highlights the major results. The simulations were conducted at the Multi-Axial Full-Scale Sub-Structured Testing and Simulation Facility at the University of Illinois, which is part of the National Science Foundation Network for Earthquake Engineering Simulation.
Keywords: Earthquake, Hybrid Simulation, Large Scale, Theory, Algorithms, Experimental
Authors: Oh-Sung Kwon; Amr S. Elnashai; Billie F. Spencer
DOI: 10.12989/sem.2008.30.3.331
Abstract: A framework for multi-platform analytical and multi-component hybrid (testing-analysis) simulations is described in this paper and illustrated with several application examples. The framework allows the integration of various analytical platforms and geographically distributed experimental facilities into a comprehensive pseudo-dynamic hybrid simulation. The object-oriented architecture of the framework enables easy inclusion of new analysis platforms or experimental models, and the addition of a multitude of auxiliary components, such as data acquisition and camera control. Four application examples are given, namely; (i) multi-platform analysis of a bridge with soil and structural models, (ii) multiplatform, multi-resolution analysis of a high-rise building, (iii) three-site small scale frame hybrid simulation, and (iv) three-site large scale bridge hybrid simulation. These simulations serve as illustrative examples of collaborative research among geographically distributed researchers employing different analysis platforms and testing equipment. The versatility of the framework, ease of including additional modules and the wide application potential demonstrated in the paper provide a rich research environment for structural and geotechnical engineering.
Keywords: Hybrid Simulation, Large Scale, Experimental
Authors: Oh-Sung Kwon; Narutoshi Nakata; Amr Elnashai; and Bill Spencer
DOI: 10.1080/13632460509350564
Abstract: In this technical note, the development of a framework for multi-site distributed simulations is presented. The algorithm is suitable for any combination of physical (laboratory) and analytical (computer) distributed simulations of structures, their foundations and the underlying sub-strata subjected to static and dynamic loading. Two examples of multi-site testing and multi-platform simulation are given. The main contribution in this note is the separation between time-step integration and stiffness formulation, which enables the use of static analysis and testing as modules of the main control module referred to as the simulation coordinator. The approach proposed is intuitive, simple and efficient. It is therefore recommended for use in distributed analysis using different programs, distributed testing facilities (e.g. the NEES equipment sites) or a combination of analysis and testing.
Keywords: Earthquake, Hybrid Simulation, Algorithms, Experimental
Authors: Muammer Avci; Botelho, Rui M.; and Richard Christenson
DOI: 10.12989/sss.2020.25.2.155
Abstract: This paper demonstrates a real-time hybrid substructuring (RTHS) shake table test to evaluate the seismic performance of a base isolated building. Since RTHS involves a feedback loop in the test implementation, the frequency dependent magnitude and inherent time delay of the actuator dynamics can introduce inaccuracy and instability. The paper presents a robust stability and performance analysis method for the RTHS test. The robust stability method involves casting the actuator dynamics as a multiplicative uncertainty and applying the small gain theorem to derive the sufficient conditions for robust stability and performance. The attractive feature of this robust stability and performance analysis method is that it accommodates linearized modeled or measured frequency response functions for both the physical substructure and actuator dynamics. Significant experimental research has been conducted on base isolators and dampers toward developing high fidelity numerical models. Shake table testing, where the building superstructure is tested while the isolation layer is numerically modeled, can allow for a range of isolation strategies to be examined for a single shake table experiment. Further, recent concerns in base isolation for long period, long duration earthquakes necessitate adding damping at the isolation layer, which can allow higher frequency energy to be transmitted into the superstructure and can result in damage to structural and nonstructural components that can be difficult to numerically model and accurately predict. As such, physical testing of the superstructure while numerically modeling the isolation layer may be desired. The RTHS approach has been previously proposed for base isolated buildings, however, to date it has not been conducted on a base isolated structure isolated at the ground level and where the isolation layer itself is numerically simulated. This configuration provides multiple challenges in the RTHS stability associated with higher physical substructure frequencies and a low numerical to physical mass ratio. This paper demonstrates a base isolated RTHS test and the robust stability and performance analysis necessary to ensure the stability and accuracy. The tests consist of a scaled idealized 4-story superstructure building model placed directly onto a shake table and the isolation layer simulated in MATLAB/Simulink using a dSpace real-time controller.
Keywords: Earthquake, RTHS, Experimental
Authors: Michael J. Harris; and Richard E. Christenson
DOI: 10.1007/978-3-030-12184-6_19
Abstract: Spacecraft are subjected to a variety of extreme loads during the course of a mission. One period during which these demanding loads are observed occurs during the parachute deployment stage of reentry. The deployment process utilizes a mortar in order to deploy the parachute and the corresponding reaction forces from deployment generate large impulsive loads on the spacecraft and cause vibrations throughout the spacecraft. Accurate prediction of the forces exerted on the spacecraft during deployment is paramount to the design and safety of the spacecraft. Typically the time history of the reaction forces exerted during parachute deployment are measured experimentally using a tripod-mounted mortar assembly. This approach introduces coupling between the force generated by the mortar and the dynamics of the tripod legs, and does not account for the structural compliance of the actual spacecraft system. This will lead to erroneous results if compared to the true reaction forces observed during the in-service deployment of the parachute during reentry. In this paper, a cyber-physical test procedure called real-time hybrid substructuring (RTHS) is utilized to test examine the reaction forces which occurred during the parachute deployment of the Mars Pathfinder spacecraft. The RTHS test couples, in real-time, a numerical substructure consisting of a frequency-domain model of the Mars Pathfinder with a physical substructure consisting of a parachute being fired from a mortar in the Shock and Vibration Laboratory at the University of Connecticut. Reaction forces during parachute deployment was tested for both a fixed-base scenario as well as in the case where the dynamics of the spacecraft hull were incorporated into the test. The Mars Pathfinder RTHS test demonstrates a new approach in aerospace testing that can allow for component testing during the design phase to provide more realistic load profiles and dynamic responses of critical components of the spacecraft.
Keywords: RTHS, Experimental
Authors: Connor Ligeikis; and Richard Christenson
DOI: 10.1007/978-3-030-12075-7_27
Abstract: In hybrid substructuring, a structural system is partitioned into a numerical substructure and a physical substructure. Typically, the physical substructure consists of a system component whose behavior is difficult to model while the numerical substructure consists of a computational model of the remainder of the system. Hybrid substructuring has previously been shown to be an effective method to quantify the effect of parametric uncertainties in the numerical substructure on the response of the system. This paper proposes and implements a methodology where the effect of parametric uncertainty can also be incorporated into the physical substructure. This idea is implemented in a series of small-scale Real-Time Hybrid Substructuring (RTHS) tests on a magneto-rheological fluid damper used to control a two degree-of-freedom mass-spring system. The physical current supplied to the damper is treated as a random variable. Using the RTHS test results, a metamodel of the system’s frequency domain behavior is developed using Principal Component Analysis and Kriging. This metamodel is then used to evaluate probabilistic system performance.
Keywords: RTHS, UQ
Authors: Connor Ligeikis; Alex Freeman; and Richard Christenson
DOI: 10.1007/978-3-319-74793-4_11
Abstract: The propagation of uncertainties through complex systems is a challenging endeavor. While numerical simulations can be used to accurately predict the dynamic performance of structural systems, there are some instances where the dynamics and uncertainties of specific components may be less understood or difficult to accurately model. This paper will implement a structural reliability assessment employing the cyber-physical real-time hybrid substructuring (RTHS) method to combine a numerical model of a larger structural system, incorporating uncertainty in specific parameters, with a physical test specimen of a component of the system while fully incorporating the system-level dynamic interactions and uncertainty propagation. This RTHS approach will allow for uncertainty and reliability to be addressed in the early stage of the design process as components become available and the remainder of the system remains numerically modeled. A small-scale RTHS experiment will be used to demonstrate the probability of failure of a spring-mass-damper system with a relatively small number of component tests by employing the previously proposed Adaptive Kriging-Hybrid Simulation (AK-HS) reliability method.
Keywords: RTHS, UQ, Experimental
Authors: Michael J. Harris; and Richard E. Christenson
DOI: 10.1007/978-3-319-74642-5_8
Abstract: Spacecraft are subjected to a variety of extreme loads during the course of a mission. One such demanding period during reentry is parachute deployment when a mortar on the spacecraft is used to deploy the parachute. Firing the mortar to expel the parachute imparts an impulsive force on the spacecraft and results in vibration throughout the spacecraft. Successful deployment of the parachute is critical to the success of the mission, and accurate prediction of the impulsive forces exerted on the spacecraft during deployment is paramount to the design and safety of the spacecraft. Typically the time history of the reaction force of the mortar is measured experimentally using a rigid mounting system. This approach neglects the structural compliance of the spacecraft and thus neglects the dynamic interaction between the mortar and spacecraft. This may lead to differences between the force profile observed during laboratory testing and those observed during the mission of the spacecraft. In this paper, a cyber-physical test procedure called real-time hybrid substructuring (RTHS) is proposed to test the parachute deployment of the Mars Pathfinder spacecraft. The proposed RTHS test couples, in real-time, a numerical substructure, consisting of a dynamic model of the Mars Pathfinder with a physical substructure, consisting of a mortar being fired in the Shock and Vibration Laboratory at the University of Connecticut. The proposed RTHS test will be shown to fully capture the effect of spacecraft compliance on the force profile generated during the mortar firing. The Mars Pathfinder RTHS test is used to demonstrate this new approach in aerospace testing that can allow for component testing during the design phase to provide more realistic load profiles and more certain dynamic response at critical locations throughout the spacecraft.
Keywords: RTHS, Experimental
Authors: Muammer Avci; and Richard Christenson
DOI: 10.1007/978-3-319-74654-8_6
Abstract: This paper present a real-time hybrid substructuring (RTHS) shake table test to evaluate the seismic performance of a base isolated building. Significant experimental research has been conducted on base isolators and dampers toward developing high fidelity numerical models. Shake table testing where the building superstructure is tested while the isolation layer is numerically modeled can allow for a range of isolation strategies to be examined for a single shake table experiment. Further, recent concerns in base isolation for long period, long duration earthquakes necessitate adding damping at the isolation layer which can allow higher frequency energy to be transmitted into the superstructure and can result in damage to structural and nonstructural components that can be difficult to numerically model and accurately predict. As such, physical testing of the superstructure while numerically modeling the isolation layer may be desired. The RTHS approach has been previously proposed for base isolated buildings, however, to date it has not been conducted on base isolated structure isolated at the ground level and where the isolation layer itself is numerically simulated. This configuration provides multiple challenges associated with higher physical substructure frequencies and a low numerical to physical mass ratio. This paper demonstrates a base isolated RTHS test with a scaled idealized 4-story superstructure building model placed directly onto a shake table and the isolation layer simulated in MATLAB/Simulink using a dSpace real-time controller.
Keywords: Earthquake, RTHS, Experimental
Authors: Rui Botelho; and Richard E. Christenson
DOI: 10.1121/1.4877728
Abstract: Real-time hybrid substructuring (RTHS) is a relatively new method of vibration testing that allows a coupled dynamic system to be partitioned into separate physical and numerical components or substructures. The physical and numerical substructures are interfaced together in real-time as a closed-loop hybrid experiment similar to hardware-in-the-loop (HWIL) testing, whereby the physical substructure is tested concurrently with a numerical simulation of the remaining system. This work describes uniaxial RTHS testing at the University of Connecticut Structures Research Laboratory applied to simplified fluid-loaded structural systems. These tests use a physical one degree of freedom (DOF) mass-spring system coupled to a fluid-loaded analytical substructure. One test uses a fluid-loaded plate as the analytical substructure, while another test uses a fluid-loaded cylinder. An overview of RTHS is also presented, including the details of the feedback control architecture for coupling physical and analytical substructures together using servo-hydraulic actuation with a model-based minimum-phase inverse compensation (MPIC) of the actuator dynamics. In addition, a convolution integral (CI) method for solving the fluid-loaded analytical substructures in real-time is described. Experimental results demonstrate that RTHS can accurately capture the dynamic interaction of a fluid-loaded structural system and provide physical insight into the coupled response.
Keywords: RTHS, Experimental
Authors: Zhaoshuo Jiang; Sung Jig Kim; Shelley Plude; and Richard Christenson
DOI: 10.1088/0964-1726/22/10/105008
Abstract: Magneto-rheological (MR) fluid dampers can be used to reduce the traffic induced vibration in highway bridges and protect critical structural components from fatigue. Experimental verification is needed to verify the applicability of the MR dampers for this purpose. Real-time hybrid simulation (RTHS), where the MR dampers are physically tested and dynamically linked to a numerical model of the highway bridge and truck traffic, provides an efficient and effective means to experimentally examine the efficacy of MR dampers for fatigue protection of highway bridges. In this paper a complex highway bridge model with 263 178 degrees-of-freedom under truck loading is tested using the proposed convolution integral (CI) method of RTHS for a semiactive structural control strategy employing two large-scale 200 kN MR dampers. The formation of RTHS using the CI method is first presented, followed by details of the various components in the RTHS and a description of the implementation of the CI method for this particular test. The experimental results confirm the practicability of the CI method for conducting RTHS of complex systems.
Keywords: Earthquake, RTHS, Large Scale, Experimental
Authors: Tao Wang; Gilberto Mosqueda; Andres Jacobsen; and Maria Cortes‐Delgado
DOI: 10.1002/eqe.1130
Abstract: A hybrid numerical and experimental simulation to collapse was conducted on a one‐half scale moment‐resisting frame building with two experimental substructures at different locations. An extensible hybrid test framework was used that adopts a generalized interface to encapsulate each numerical or tested substructure, through which only boundary displacements and forces are exchanged. Equilibrium and compatibility between substructures are enforced by an iterative quasi‐Newton procedure, while adopting a predictor‐and‐corrector method to avoid loading reversals on physically tested substructures. To overcome difficulties in controlling stiff axial and rotational deformations at the boundaries, the flexible test scheme employs either open‐loop or closed‐loop control at the boundaries: enforcing either compatibility or equilibrium, or both requirements at critical boundaries. The effectiveness of the extensible framework and its capability to simulate structural behavior through collapse is demonstrated by a geographically distributed test that reproduced the collapse behavior of a four‐story, two‐bay, steel moment frame previously tested on an earthquake simulator. A comparison of both experiments highlights the viability of the hybrid test as an effective tool for the performance evaluation of structural systems from the onset of damage through collapse.
Keywords: Earthquake, Hybrid Simulation, Experimental
Authors: Alireza Sarebanha; Andreas H. Schellenberg; Matthew J. Schoettler; Gilberto Mosqueda; and Stephen A. Mahin
DOI: 10.32604/cmes.2019.04846
Abstract: Hybrid simulation can be a cost effective approach for dynamic testing of structural components at full scale while capturing the system level response through interactions with a numerical model. The dynamic response of a seismically isolated structure depends on the combined characteristics of the ground motion, bearings, and superstructure. Therefore, dynamic full-scale system level tests of isolated structures under realistic dynamic loading conditions are desirable towards a holistic validation of this earthquake protection strategy. Moreover, bearing properties and their ultimate behavior have been shown to be highly dependent on rate-of-loading and scale size effects, especially under extreme loading conditions. Few laboratory facilities can test full-scale seismic isolation bearings under prescribed displacement and/or loading protocols. The adaptation of a full-scale bearing test machine for the implementation of real-time hybrid simulation is presented here with a focus on the challenges encountered in attaining reliable simulation results for large scale dynamic tests. These advanced real-time hybrid simulations of large and complex hybrid models with several thousands of degrees of freedom are some of the first to use high performance parallel computing to rapidly execute the numerical analyses. Challenges in the experimental setup included measured forces contaminated by delay and other systematic control errors in applying desired displacements. Friction and inertial forces generated by the large-scale loading apparatus can affect the accuracy of measured force feedbacks. Reliable results from real-time hybrid simulation requires implementation of compensation algorithms and correction of these various sources of errors. Overall, this research program confirms that real-time hybrid simulation is a viable testing method to experimentally assess the behavior of full-scale isolators while capturing interactions with the numerical models of the superstructure to evaluate system level and in-structure response.
Keywords: Earthquake, RTHS, Large Scale, Algorithms, Experimental
Authors: M. Javad Hashemi; and Gilberto Mosqueda
DOI: 10.1002/eqe.2427
Abstract: Hybrid simulation combines numerical and experimental methods for cost‐effective, large‐scale testing of structures under simulated dynamic earthquake loads. Particularly for experimental seismic collapse simulation of structures, hybrid testing can be an attractive alternative to earthquake simulators due to the limited capacity of most facilities and the difficulties and risks associated with a collapsing structure on a shaking table. The benefits of hybrid simulation through collapse can be further enhanced through accurate and practical substructuring techniques that do not require testing the entire structure. An innovative substructuring technique for hybrid simulation of structures subjected to large deformations is proposed to simplify the boundary conditions by overlapping the domains between the numerical and experimental subassemblies. The advantages of this substructuring technique are the following: it requires only critical components of the structure to be tested experimentally; it reduces the number of actuators at the interface of the experimental subassemblies; and it can be implemented using typically available equipment in laboratories. Compared with previous overlapping methods that have been applied in hybrid simulation, this approach requires additional sensing in the hybrid simulation feedback loop to obtain internal member forces, but provides significantly better accuracy in the highly nonlinear range. The proposed substructuring technique is verified numerically and validated experimentally, using the response of a four‐story moment‐resisting frame that was previously tested to collapse on an earthquake simulator.
Keywords: Earthquake, Hybrid Simulation, Nonlinear, Large Scale, Experimental
Authors: Sung Jig Kim; Richard E Christenson; Steven F Wojtkiewicz; and Erik A Johnson
DOI: 10.1088/0964-1726/20/2/025024
Abstract: This paper proposes a real-time hybrid simulation method that will allow complex systems to be tested within the hybrid test framework by employing the convolution integral (CI) method. The proposed CI method is potentially transformative for real-time hybrid simulation. The CI method can allow real-time hybrid simulation to be conducted regardless of the size and complexity of the numerical model and for numerical stability to be ensured in the presence of high frequency responses in the simulation. This paper presents the general theory behind the proposed CI method and provides experimental verification of the proposed method by comparing the CI method to the current integration time-stepping (ITS) method. Real-time hybrid simulation is conducted in the Advanced Hazard Mitigation Laboratory at the University of Connecticut. A seismically excited two-story shear frame building with a magneto-rheological (MR) fluid damper is selected as the test structure to experimentally validate the proposed method. The building structure is numerically modeled and simulated, while the MR damper is physically tested. Real-time hybrid simulation using the proposed CI method is shown to provide accurate results.
Keywords: Earthquake, RTHS, Theory, Experimental
Authors: Rui M. Botelho; Joseph A. Franco; and Richard E. Christenson
DOI: 10.1115/NCAD2015-5922
Abstract: Real-time hybrid substructuring (RTHS) is a relatively new method of vibration testing for characterizing the system-level performance of physical hardware components. With RTHS, a dynamic system is partitioned into physical and numerical substructures and interfaced together in real-time similar to hardware-in-the-loop testing. This paper presents an overview of RTHS including the challenges posed by its real-time constraints and the application to system-level testing of physical vibration control devices and mechanical equipment. Two laboratory RTHS experiments performed at the University of Connecticut Structures Research Laboratory are used to demonstrate the benefit of RTHS. The first test examines the connected control method using viscous damper hardware as the physical substructure coupled to adjacent base isolation systems as the numerical substructure. The second test involves a multi-stage isolation system comprised of an operating mechanical component on isolators as the physical substructure coupled to an intermediate mass on similar isolators as the numerical substructure. In these RTHS tests, feedforward inverse compensation combined with feedback is used to compensate the frequency-dependent dynamics of the multi-actuator system. Experimental results demonstrate that RTHS accurately captures the system-level behavior of the coupled system and allows for repeatable tests of various conditions and potential system improvements to be efficiently examined.
Keywords: RTHS, Experimental
Authors: Joseph A. Franco; Rui M. Botelho; and Richard E. Christenson
DOI: 10.1007/978-3-319-29763-7_3
Abstract: In the design of mechanical systems, there are constraints imposed on the vibration of mechanical equipment to limit the vibration transmission into its support structure. To accurately predict the coupled system response, it is important to capture the coupled interaction of the two portions, i.e., the mechanical equipment and the support structure, of the mechanical system. Typically during a design, the analysis of the full mechanical system is not possible because a large part of the system may be non-existent. Existing methods known as Transfer Path Analysis and Frequency Based Substructuring are techniques for predicting the coupled response of vibrating mechanical systems. In this paper, a control based hybrid substructuring approach to Transfer Path Analysis is proposed. By recognizing the similarities between feedback control and dynamic substructuring, this paper demonstrates that this approach can accurately predict the coupled dynamic system response of multiple substructured systems including operating mechanical equipment with a complex vibration source. The main advantage of this method is that it uses blocked force measurements in the form of a power spectral density matrix measured uncoupled from the rest of the system. This substructuring method is demonstrated using a simplified case study comprised of a two-stage vibration isolation system and excited by operating mechanical equipment.
Keywords: Hybrid Simulation, Experimental, Transfer Systems
Authors: Sung Jig Kim; Richard Christenson; Brian Phillips; and B. F. Spencer, Jr.
DOI: 10.1061/9780784412374.034
Abstract: In the field of earthquake engineering, and more generally in structural dynamics and control, experimental verification is critical. For large structural systems, full-scale experimental tests may not be economically or practically feasible. However, hybrid simulation (where the simulation is partitioned into numerical and physical components), provides the capability to isolate and physically test critical components of a structure in an efficient manner, while still fully capturing the dynamic behavior of an interaction with the entire structural system. Real-time hybrid simulation (RTHS) conducts these tests in hard, real-time to ensure that any rate-dependant characteristics of the physical component are accurately represented. Furthermore, testing at multiple geographically distributed laboratories can optimize the use of distributed resources found in the Network for Earthquake Engineering Simulation (NEES) equipment facilities. Leveraging multiple equipment sites for RTHS poses great challenges due to the hard real-time nature of RTHS and the inherent and unpredictable network delay associated with geographically distributed testing. This paper describes the framework, sensitivity analysis, and resulting tests of a series of geographically distributed RTHS successfully conducted between the University of Connecticut (UConn) and the University of Illinois (Illinois).
Keywords: Earthquake, RTHS, Experimental
Authors: Richard Christenson, A.M.ASCE; Yi Zhong Lin, S.M.ASCE; Andrew Emmons, M.ASCE; and Brent Bass, M.ASCE
DOI: 10.1061/(ASCE)0733-9445(2008)134:4(522)
Abstract: Magneto-rheological (MR) fluid dampers have been identified as a particularly promising type of semiactive control device for hazard mitigation in civil engineering structures. Large-scale experimental testing is important to verify the performance of MR fluid dampers for seismic protection of civil structures. Real-time hybrid testing, where only the critical components of the system are physically tested while the rest of the structure is simulated, can provide a cost-effective means for large-scale testing of semiactive controlled structures. This paper describes the real-time hybrid simulation experimental setup for multiple large-scale MR fluid dampers and demonstrates the capability at the University of Colorado at Boulder shared-use Fast Hybrid Test facility to conduct real-time hybrid testing within the Network for Earthquake Engineering Simulation.
Keywords: Earthquake, RTHS, Large Scale, Experimental
Authors: Xiaoyun Shao, P.E., M.ASCE; Adam Mueller; and Bilal Ahmed Mohammed
DOI: 10.1061/(ASCE)EM.1943-7889.0000987
Abstract: Hybrid simulations have shown great potential for economic and reliable assessment of structural seismic performance by combining physical experimentation on part of the structural system and numerical simulation of the remaining structural components. Current hybrid simulation practices often use a fixed numerical model without considering the possible availability of a more-accurate model obtained during hybrid simulation through an online model updating technique. To address this limitation and improve the reliability of numerical models in hybrid simulations, this paper presents a method and an implementation procedure of conducting real-time hybrid simulation (RTHS) with online model updating. The Unscented Kalman Filter (UKF) was adopted as the parameter identification algorithm applied to the Bouc-Wen model that defines the hysteresis of the experimental substructure. The identified parameters are then used to update the models of the numerical substructures during RTHS. A parametric study of the UKF system model parameters is carried out first to determine the optimum values to be used in the verification experiments. Then RTHS of a three-story steel shear building model is conducted and the effectiveness of online model updating in RTHS and the proposed implementation procedure is demonstrated. Guidelines for implementing the UKF for online model updating in RTHS and research needs for further development are discussed.
Keywords: Earthquake, RTHS, Model Updating, Nonlinear, Algorithms, Experimental
Authors: Shao, Xiaoyun; van de Lindt; Bahmani, Pouria; Pang, Weichiang; Ziaei, Ershad; Symans, Michael; Tian, Jingjing; Dao, Thang
DOI: 10.12989/sss.2014.14.6.1031
Abstract: Real-time hybrid simulation (RTHS) of a stacked wood shear wall retrofitted with a rate-dependent seismic energy dissipation device (viscous damper) was conducted at the newly constructed Structural Engineering Laboratory at the University of Alabama. This paper describes the implementation process of the RTHS focusing on the controller scheme development. An incremental approach was adopted starting from a controller for the conventional slow pseudodynamic hybrid simulation and evolving to the one applicable for RTHS. Both benchmark-scale and full-scale tests are discussed to provide a roadmap for future RTHS implementation at different laboratories and/or on different structural systems. The developed RTHS controller was applied to study the effect of a rate-dependent energy dissipation device on the seismic performance of a multi-story wood shear wall system. The test specimen, setup, program and results are presented with emphasis given to inter-story drift response. At 100% DBE the RTHS showed that the multi-story shear wall with the damper had 32% less inter-story drift and was noticeably less damaged than its un-damped specimen counterpart.
Keywords: Earthquake, Hybrid Simulation, RTHS, Experimental, Controller Design, Benchmark
Authors: X. Shao; and A. M. Reinhorn
DOI: 10.1080/13632469.2011.597487
Abstract: Force-based real-time hybrid simulation is a seismic experimental method that combines physical testing using shake tables and dynamic actuators with numerical analysis. The unique aspect of this force-based formulation is that various hybrid simulation techniques, such as dynamic, pseudo-dynamic, and quasi-dynamic testing, can be similarly executed. To implement such a method, the hardware components and the corresponding software were designed and integrated into a modular controller platform. This article focuses on the implementation issues of such formulation. A pilot scale setup was assembled to conduct proof of concept experiments of the controller platform and is presented herein.
Keywords: Earthquake, Hybrid Simulation, RTHS, Experimental, Controller Design
Authors: Xiaoyun Shao, A.M.ASCE; Andrei M. Reinhorn, F.ASCE; and Mettupalayam V. Sivaselvan
DOI: 10.1061/(ASCE)ST.1943-541X.0000314
Abstract: The development and implementation of the real-time hybrid simulation (RTHS), a seismic response simulation method with a combination of numerical computation and physical specimens excited by shake tables and auxiliary actuators, are presented. The structure to be simulated is divided into one or more experimental and computational substructures. The loadings generated by the seismic excitations at the interfaces between the experimental and computational substructures, in terms of accelerations and forces, are imposed by shake tables and actuators in a step-by-step manner at a real-time rate. The measured displacement and velocity responses of the experimental substructure are fed back to determine the loading commands of the next time step. The unique aspect of the aforementioned hybrid simulation method is the versatile implementation of inertia forces and a force-based substructuring. The general formulation of RTHS enables this hybrid simulation method being executed as real-time pseudodynamic (PSD) testing, dynamic testing, and a combination of both, depending on the availability of the laboratory testing equipment and their capacity. The derivation of the general formulation and the corresponding testing system are presented in this paper. Numerical simulation and physical experiment were conducted on the RTHS of a three-story structural model. Simulation and experimental results verify the concept of the proposed general formulation of RTHS and the feasibility of the developed corresponding controller platform.
Keywords: Earthquake, RTHS, Experimental, Controller Design
Authors: Weihua Su; and Wei Song
DOI: 10.1016/j.ast.2019.105513
Abstract: The concept of real-time hybrid aeroelastic simulation for flexible wings is introduced in this paper. In a hybrid aeroelastic simulation, a coupled aeroelastic system is “broken down” into an aerodynamic simulation subsystem and a structural vibration subsystem. The coupling between structural dynamics and aerodynamics is maintained by the real-time communication between the two subsystems. As the vibration of the testing article (a wing member or a full aircraft) is actuated by actuators, hybrid aeroelastic simulation and experiment can eliminate the sizing constraint of the conventional aeroelastic testing performed within a wind-tunnel. It also significantly saves the cost of wind-tunnel testing. However, several critical technical problems (such as process noise, measurement noise, and actuator delay) need to be addressed to enable a hybrid simulation in real-time. This paper proves the concept of real-time hybrid simulation and discusses some of the critical problems underlying the technique.
Keywords: Wind, RTHS, Experimental
Authors: Wei Song; and Weihua Su
DOI: 10.1117/12.2084431
Abstract: In performing an effective structural analysis for wind turbine, the simulation of turbine aerodynamic loads is of great importance. The interaction between the wake flow and the blades may impact turbine blades loading condition, energy yield and operational behavior. Direct experimental measurement of wind flow field and wind profiles around wind turbines is very helpful to support the wind turbine design. However, with the growth of the size of wind turbines for higher energy output, it is not convenient to obtain all the desired data in wind-tunnel and field tests. In this paper, firstly the modeling of dynamic responses of large-span wind turbine blades will consider nonlinear aeroelastic effects. A strain-based geometrically nonlinear beam formulation will be used for the basic structural dynamic modeling, which will be coupled with unsteady aerodynamic equations and rigid-body rotations of the rotor. Full wind turbines can be modeled by using the multi-connected beams. Then, a hybrid simulation experimental framework is proposed to potentially address this issue. The aerodynamic-dominant components, such as the turbine blades and rotor, are simulated as numerical components using the nonlinear aeroelastic model; while the turbine tower, where the collapse of failure may occur under high level of wind load, is simulated separately as the physical component. With the proposed framework, dynamic behavior of NREL’s 5MW wind turbine blades will be studied and correlated with available numerical data. The current work will be the basis of the authors’ further studies on flow control and hazard mitigation on wind turbine blades and towers.
Keywords: Wind, Hybrid Simulation, Nonlinear, Experimental
Authors: Saeid Hayati; and Wei Song
DOI: 10.1007/978-3-319-54777-0_27
Abstract: Real-Time Hybrid simulation (RTHS) is a powerful experimental technique which provides engineers the opportunity of performing cost-effective dynamic tests for large or full scale structures. To carry out a successful RTHS test, the time delay, which is mostly associated with the servo-hydraulic actuator dynamics, needs to be reduced by an appropriate compensator. Model-based feedforward compensators are designed based on the dynamic model of the plant, including both the servo-hydraulic actuator and the specimen attached to it. This dynamic model may not represent the plant accurately during the RTHS, especially when the specimen behaves nonlinearly during the test. As a result, the feedforward compensator/controller which is designed based on this plant model may not work effectively. In this paper, a discrete time feedback controller is introduced, in addition to the feedforward compensator, to provide robustness to the delay compensation. Both numerical and experimental studies will be conducted. The performance of this feedforward-feedback compensator is evaluated through the actuator time delay and the relative Root-Mean-Square (RMS) error between the desired and measured actuator displacement.
Keywords: RTHS, Nonlinear, Experimental, Controller Design
Authors: Gaetano Miraglia; Milos Petrovic; Giuseppe Abbiati; Nebojsa Mojsilovic; and Bozidar Stojadinovic
DOI: 10.1002/eqe.3262
Abstract: Testing of stiff physical substructures (PSs) still poses major technical issues that prevent from adopting hybrid simulation (HS) as a standard structural testing method. Firstly, elastic deformation of reaction frames, as well as the limited resolution of displacement transducers, deteriorate displacement control accuracy. Secondly, as a consequence of control errors, small perturbations of actuator displacements entail large restoring force oscillations that spuriously excite the higher eigenmodes of the hybrid model. For this reason, in the current practice, force‐controlled hydraulic jacks handle vertical degrees of freedom, which are typically associated with stiff axially loaded members and excluded from the time integration loop. Vertical forces are either kept constant or adjusted during the experiment based on simplified redistribution rules. Besides deterioration of displacement control accuracy, stiff PSs naturally increase the frequency bandwidth of the hybrid model, whose higher eigenfrequencies (divided by the testing time scale) may fall outside the frequency bandwidth of the actuation system, thus destabilizing the HS. This is a collateral issue to which, in the authors' knowledge, no sufficient attention as been dedicated yet, and this paper tries to address it. From this standpoint, we propose component‐mode synthesis as a rigorous approach for deriving reduced‐order physical and numerical substructure mass and stiffness matrices that minimize the frequency bandwidth of the hybrid model. The proposed methodology allowed for performing HSs of a load‐bearing unreinforced masonry structure including both horizontal and vertical degrees of freedom with a standard three‐actuator setup used for cyclic testing.
Keywords: Earthquake, Hybrid Simulation, Experimental
Authors: Masayoshi Nakashima
DOI: 10.1002/eqe.3274
Abstract: This historical note reports on the early days of the development of an experimental method called “hybrid simulation.” As background, the seeds of this concept, initiated in the early 1970s by Japanese researchers, are presented first, followed by initial efforts (regarded as Stage I) to realize the concept of hybrid simulation and its first applications to explore the seismic performance of structures. The initial research in this now‐seminal field of earthquake engineering began in the early 1970s by Koichi Takanashi and his coworkers at the Institute of Industrial Science, the University of Tokyo. Their highly notable efforts in laying the groundwork for hybrid simulation occurred in the mid‐1970s through the early 1980s by Takanashi (for steel structures) and Tsuneo Okada (for RC structures). These two men and their coworkers first applied hybrid simulation to explore the seismic behavior, performance, and design of various types of building structures. In Stage I, this method was called “the on‐line computer‐controlled test” or “pseudo dynamic test” because the unique feature of the method was the combined test and simulation and the intentional slow loading in the test. Extension of the scope and application of hybrid simulation occurred largely between the early 1980s and the early 1990s (regarded as Stage II) in conjunction with the United States–Japan joint research project. A few notable efforts made around that period are touched upon briefly, including error propagation and suppression in multi‐degree‐of‐freedom hybrid simulation, application of the substructure methodology to hybrid simulation, and real‐time hybrid simulation.
Keywords: Earthquake, Hybrid Simulation, Experimental
Authors: Kung‐Juin Wang; Ming‐Chieh Chuang; Keh‐Chyuan Tsai; Chao‐Hsien Li; Pu‐Yuan Chin; and Shen‐Yuo Chueh
DOI: 10.1002/eqe.3139
Abstract: This paper describes a series of hybrid tests performed on a steel panel damper (SPD) specimen by using a multi‐axial testing system. The building under investigation adopted a three‐dimensional six‐story moment resisting frame with four SPDs installed at each story as the main seismic resisting system. The structural model was subjected to bi‐directional ground excitations of three hazard levels. The finite element analysis program “Platform of Inelastic Structural Analysis for 3D Systems” (PISA3D) was used as the analysis kernel for hybrid tests. Relevant programming extensions in PISA3D were created to support geographically distributed hybrid testing in a general‐purpose manner. An external displacement control (EDC) method was developed such that the actual boundary deformation of the specimen fixtures could be continuously measured and immediately compensated during tests. An online model updating (OMU) technique was developed and employed such that the material properties of the specimen could be identified directly from the specimen response during the test. The identified material properties were then immediately used to update those of the other relevant numerical elements to enhance the overall simulation fidelity. Superior flexibility of the underlying software architecture was well demonstrated in this series of hybrid tests since no hardcoding was used to support all the complex test settings. Test results confirmed the effectiveness of the proposed EDC method, as well as the capacity of the proposed OMU technique to satisfactorily and efficiently capture the hysteretic properties of the specimen.
Keywords: Earthquake, Hybrid Simulation, Model Updating
Authors: Aikaterini Stefanaki; M. V. Sivaselvan
DOI: 10.1002/eqe.3039
Abstract: Dynamic substructuring refers to physical testing with computational models in the loop. This paper presents a new strategy for such testing. The key feature of this strategy is that it decouples the substructuring controller from the physical subsystem. Unlike conventional approaches, it does not explicitly include a tracking controller. Consequently, the design and implementation of the substructuring controls are greatly simplified. This paper motivates the strategy and discusses the main concept along with details of the substructuring control design. The focus is on configurations that use shake tables and active mass drivers. An extensive experimental assessment of the new strategy is presented in a companion paper, where the influence of various factors such as virtual subsystem dynamics, control gains, and nonlinearities is investigated, and it is shown that robustly stable and accurate substructuring is achieved.
Keywords: Hybrid Simulation, Controller Design
Authors: Aikaterini Stefanaki; M. V. Sivaselvan; Scot Weinreber; and Mark Pitman
DOI: 10.1002/eqe.3041
Abstract: This paper is on an extensive experimental evaluation program to explore the robustness of a new strategy dynamic substructuring. This strategy, in contrast to conventional approaches, decouples the substructuring controller from the physical subsystem, and consequently results in a simple, yet robust, implementation. The concept is presented in detail in a companion paper. A configuration consisting of a shake table and an active mass driver is used in the experimental program, and various factors such as dynamics of virtual subsystems used, modeling of the actuator, choice of control gain settings, and nonlinear effects in the actuator are investigated, leading to the conclusion that the proposed strategy results in robust performance.
Keywords: Hybrid Simulation, Nonlinear, Experimental, Controller Design
Authors: Bin Wu; Xizhan Ning; Guoshan Xu; Zhen Wang; Zhu Mei; and Ge Yang
DOI: 10.1002/eqe.2996
Abstract: Hybrid simulation is a powerful and cost‐effective simulation technique to evaluate structural dynamic performance. However, it is sometimes rather difficult to guarantee all the boundaries on the physical substructures, especially when the boundary conditions are very complex, due to limited laboratory resources. Lacking of boundary conditions is bound to change the stress state of the structure and eventually result in an inaccurate evaluation of structural performance. A model updating‐based online numerical simulation method is proposed in this paper to tackle the problem of incomplete boundary conditions. In the proposed method, 2 sets of finite element models with the same constitutive model are set up for the overall analysis of the whole structure and the constitutive model parameter estimation of the physical substructure, respectively. The boundary conditions are naturally satisfied because the response is calculated from the overall structural model, and the accuracy is improved as the material constitutive parameters are updated. The effectiveness of the proposed method is validated via numerical simulations and actual hybrid tests on a RC frame structure, and the results show that the negative effect of incomplete boundary conditions is almost eliminated and the accuracy of hybrid simulation is very much improved.
Keywords: Hybrid Simulation, Model Updating
Authors: Ming‐Chieh Chuang; Shang‐Hsien Hsieh; Keh‐Chyuan Tsai; Chao‐Hsien Li; Kung‐Juin Wang; and An‐Chien Wu
DOI: 10.1002/eqe.2950
Abstract: To improve the efficiency of model fitting, parameter identification techniques have been actively investigated. Recently, the applications of parameter identification migrated from off‐line model fitting to on‐line model updating. The objective of this study is to develop a gradient‐based method for model updating to advance hybrid simulation also called hybrid test. A novel modification of the proposed method, which can reduce the number of design variables to improve the identification efficiency, is illustrated in detail. To investigate the model updating, simulated hybrid tests were conducted with a 5‐story steel frame equipped with buckling‐restrained braces (BRBs) utilized in the shaking table tests conducted in E‐Defense in Japan in 2009. The calibrated analytical model that was verified with the test results can serve as the reference model. In the simulated hybrid tests, the physical BRB substructure is numerically simulated by utilizing a truss element with the 2‐surface model identical to the part of the reference model. Such numerical verification allows simulation of measurement errors for investigation on the performance of the proposed method. Moreover, the feasibility of sharing the identified parameter values, which were obtained from the physical substructure responses, with the relevant numerical models is also verified with the artificial component responses derived from the physical experiments.
Keywords: Hybrid Simulation, Model Updating, Experimental
Authors: T.Y. Yang; Dorian P. Tung; Yuanjie Li; Jian Yuan Lin; Kang Li; and Wei Guo
DOI: 10.1002/eqe.2920
Abstract: Hybrid simulation (HS) is a novel technique to combine analytical and experimental sub‐assemblies to examine the dynamic responses of a structure during an earthquake shaking. Traditionally, HS uses displacement‐based control where the finite element program calculates trial displacements and applies them to both the analytical and experimental sub‐assemblies. Displacement‐based HS (DHS) has been proven to work well for most structural sub‐assemblies. However, for specimens with high stiffness, traditional DHS does not work because it is difficult to precisely control hydraulic actuators in small displacement. A small control error in displacement will result in large force response fluctuations for stiff specimens. This paper resolves this challenge by proposing a force‐based HS (FHS) algorithm that directly calculates trial forces instead of trial displacements. The proposed FHS is finite element based and applicable to both linear and nonlinear systems. For specimens with drastic changes in stiffness, such as yielding, a switch‐based HS (SHS) algorithm is proposed. A stiffness‐based switching criterion between the DHS and FHS algorithms is presented in this paper. All the developed algorithms are applied to a simple one‐story one‐bay concentrically braced moment frame. The result shows that SHS outperforms DHS and FHS. SHS is then utilized to validate the seismic performance of an innovative earthquake resilient fused structure. The result shows that SHS works in switching between the DHS and FHS modes for a highly nonlinear and highly indeterminate structural system.
Keywords: Earthquake, Hybrid Simulation, Nonlinear, Theory, Algorithms, Experimental
Authors: Justin A. Murray; and Mehrdad Sasani
DOI: 10.1002/eqe.2828
Abstract: Reinforced concrete frame structures built prior to the mid‐1970s are susceptible to brittle column failure under seismic action, potentially leading to progressive collapse of the structure. The behavior of columns susceptible to brittle shear‐axial failure has been studied previously but rarely has the interaction between damaged columns and the surrounding three‐dimensional structure been investigated experimentally and at full scale. In this study, as the second in a series of hybrid simulations, two full‐scale reinforced concrete columns of a representative pre‐1970s structure were tested at the Multi‐axial Full‐scale Substructure Testing and Simulation (MUST‐SIM) laboratory. Through the use of hybrid simulation, the interaction of the columns with the surrounding structure is studied under a severe seismic motion including vertical excitation. The computational model representing the remainder of the representative 10‐story structure is created in the computer program OpenSees. During the hybrid simulation, both physical specimens experience significant loss of shear and axial strength, and the effects of these failures on the surrounding system are described. The three‐dimensional computational model in OpenSees allowed for analytical flexural‐axial failure of a third column in the structure to occur. The effects of these multiple failures on the response of a full structural system under seismic action are quantified, and the progressive collapse resistance mechanisms are discussed.
Keywords: Earthquake, Hybrid Simulation, Experimental
Authors: Maikol Del Carpio R.; Gilberto Mosqueda; and Dimitrios G. Lignos
DOI: 10.1002/eqe.2743
Abstract: A series of seismic tests were conducted on a 1½‐bay by 1½‐story special steel moment‐resisting frame subassembly from the onset of damage through incipient collapse. These tests were conducted using hybrid simulation with substructuring as a mean to demonstrate efficient testing methods for system‐level collapse assessment of large‐scale structural subassemblies. The ½‐scale specimen was designed to capture the behavior and interactions of beams, columns, panel zones, and composite floor slab. The experimental test setup permitted the application of lateral as well as varying vertical forces on the test specimen while maintaining realistic boundary conditions on the subassembly. With the overarching objective to advance knowledge on the collapse assessment of frame structures under earthquake loading, this paper focuses on the seismic performance of a steel moment‐resisting frame through collapse. The failure mechanisms of the test frame are described and compared with numerical simulations based on state‐of‐the‐art modeling approaches.
Keywords: Earthquake, Hybrid Simulation, Large Scale, Experimental
Authors: Hsen‐Han Khoo; Keh‐Chyuan Tsai; Ching‐Yi Tsai; Cheng‐Yu Tsai; and Kung‐Juin Wang
DOI: 10.1002/eqe.2696
Abstract: A two‐story buckling‐restrained brace (BRB) frame was tested under bidirectional in‐plane and out‐of‐plane loading to evaluate the BRB stability and gusset plate design. The test comprised pseudo‐dynamic loadings using the 1999 Chi‐Chi earthquake scaled to the 50%, 10%, and 2% probability of exceedance in 50 years and a cyclic regime of increasing amplitudes of up to 3.0% story drift ratio (SDR). The specimen had a unique configuration where the beams were connected to the columns through shear tabs welded to the column flanges and bolted to the beam webs. Stable hysteretic behavior with only minor cracking at the gusset‐to‐column welds was observed under the pseudo‐dynamic tests, with maximum in‐plane and out‐of‐plane SDRs of 2.24% and 1.47% respectively. Stable behavior continued into the cyclic test where fracture of the gusset‐to‐column welds occurred in the first cycle to simultaneous bidirectional SDR of 3.0%. The observed BRB stability is consistent with a methodology developed for BRB frames under simultaneous in‐plane and out‐of‐plane drifts. The specimen behavior was studied using a finite element model. It was shown that gusset plates are subjected to a combination of BRB force and frame action demands, with the latter increasing the gusset‐to‐beam and gusset‐to‐column interface demands by an average of 69% and 83% respectively. Consistent with the test results, failure at the gusset‐to‐column interfaces is computed when frame action demands are included, thus confirming that not considering frame action demands may results in unconservative gusset plate designs.
Keywords: Earthquake, Hybrid Simulation, Nonlinear
Authors: Bin Wu; Yongsheng Chen; Guoshan Xu; Zhu Mei; Tianlin Pan; and Cong Zeng
DOI: 10.1002/eqe.2706
Abstract: Hybrid simulations that combine numerical computations and physical experiment represent an effective method of evaluating the dynamic response of structures. However, it is sometimes impossible to take all the uncertain or nonlinear parts of the structure as the physical substructure. Thus, the modeling errors of the numerical part can raise concerns. One method of solving this problem is to update the numerical model by estimating its parameters from experimental data online. In this paper, an online model updating method for the hybrid simulation of frame structures is proposed to reduce the errors of nonlinear modeling of numerical substructures. To obtain acceptable accuracy with acceptable extra computation efforts as a result of model parameter estimation, the sectional constitutive model is adopted, therein considering axial‐force and bending‐moment coupling; moreover, the unscented Kalman filter is used for parameter estimation of the sectional model. The effectiveness of the sectional model updating with the unscented Kalman filter is validated via numerical analyses and actual hybrid tests on a full‐scale steel frame structure, with one column as the experimental substructure loaded by three actuators to guarantee the consistency of the boundary conditions.
Keywords: Hybrid Simulation, Nonlinear, Model Updating, Experimental
Authors: Justin A. Murray; and Mehrdad Sasani
DOI: 10.1002/eqe.2698
Abstract: Column shear‐axial failure is a complex response, which lends itself to physical experimentation. Reinforced concrete structures built prior to the mid‐1970s are particularly susceptible to such failure. Shear‐axial column failure has been examined and studied at the element level, but current rehabilitation practice equates such a column failure with structural collapse, neglecting the collapse resistance of the full structural system following column failure. This system‐level response can prevent a column failure from leading to progressive collapse of the entire structure. In this study, a hybrid simulation was conducted on a representative pre‐1970s reinforced concrete frame structure under severe seismic ground motion, in which three full‐scale reinforced concrete columns were tested at the University of Illinois at Urbana Champaign. The analytical portion of the model was represented in the computer program OpenSees. Failure occurred in multiple physical specimens as a result of the ground motion, and the hybrid nature of the test allowed for observation of the system‐level response of the tested columns and the remaining structural system. The behavior of the system accounting for multiple column shear‐axial failure is discussed and characterized.
Keywords: Earthquake, Hybrid Simulation, Large Scale, Experimental
Authors: Khalid M. Mosalam; Selim Günay; and Shakhzod Takhirov
DOI: 10.1002/eqe.2767
Abstract: In an attempt to quantify the conductor cable effect on substation electrical equipment, real‐time hybrid simulation (RTHS) is conducted on interconnected equipment using two shaking tables. For this purpose, the existing RTHS system with advanced control capabilities at the Pacific Earthquake Engineering Research Center structural laboratory is enhanced to accommodate the simultaneous use of two shaking tables. An experimental parametric study is conducted to investigate the conductor cable effect using this system with a two‐table RTHS setup. Post insulators of disconnect switches, important components of substations that are usually tested with conventional methods for evaluating their seismic performance, are utilized as experimental substructures for realistic representation of the electrical equipment. Various global and local response parameters, including accelerations, forces, displacements, and strains, are considered to evaluate the effect of the tested conductor cable configuration for a wide range of support structure configurations, which are modeled in the computer as analytical substructures. The experimental parametric study results indicate that the conductor cable has a significant effect on the response of the interconnected equipment over the whole range of investigated support structures and needs to be explicitly considered for seismic testing of electrical equipment.
Keywords: Earthquake, RTHS, Experimental
Authors: Yong Yuan; Wei Wei; Ping Tan; Akira Igarashi; Hongping Zhu; Hirokazu Iemura; and Tetsuhiko Aoki
DOI: 10.1002/eqe.2744
Abstract: In this study, a constitutive model of high damping rubber bearings (HDRBs) is developed that allows the accurate representation of the force–displacement relationship including rate‐dependence for shear deformation. The proposed constitutive model consists of two hyperelastic springs and a nonlinear dashpot element and expresses the finite deformation viscoelasticity laws based on the classical Zener model. The Fletcher–Gent effect, manifested as high horizontal stiffness at small strains and caused by the carbon fillers in HDRBs, is accurately expressed through an additional stiffness correction factor α in the novel strain energy function. Several material parameters are used to simulate the responses of high damping rubber at various strain levels, and a nonlinear viscosity coefficient η is introduced to characterize the rate‐dependent property. A parameter identification scheme is applied to the results of the multi‐step relaxation tests and the cyclic shear tests, and a three‐dimensional function of the nonlinear viscosity coefficient η with respect to the strain, and strain rate is thus obtained. Finally, to investigate the accuracy and feasibility of the proposed model for application to the seismic response assessment of bridges equipped with HDRBs, an improved real‐time hybrid simulation (RTHS) test system based on the velocity loading method is developed. A single‐column bridge was used as a test bed and HDRBs was physically tested. Comparing the numerical and RTHS results, advantage of the proposed model in the accuracy of the predicted seismic response over comparable hysteretic models is demonstrated.
Keywords: Earthquake, RTHS, Nonlinear, Experimental
Authors: Chinmoy Kolay; James M. Ricles; Thomas M. Marullo; Akbar Mahvashmohammadi; and Richard Sause
DOI: 10.1002/eqe.2484
Abstract: In real‐time hybrid simulations (RTHS) that utilize explicit integration algorithms, the inherent damping in the analytical substructure is generally defined using mass and initial stiffness proportional damping. This type of damping model is known to produce inaccurate results when the structure undergoes significant inelastic deformations. To alleviate the problem, a form of a nonproportional damping model often used in numerical simulations involving implicit integration algorithms can be considered. This type of damping model, however, when used with explicit integration algorithms can require a small time step to achieve the desired accuracy in an RTHS involving a structure with a large number of degrees of freedom. Restrictions on the minimum time step exist in an RTHS that are associated with the computational demand. Integrating the equations of motion for an RTHS with too large of a time step can result in spurious high‐frequency oscillations in the member forces for elements of the structural model that undergo inelastic deformations. The problem is circumvented by introducing the parametrically controllable numerical energy dissipation available in the recently developed unconditionally stable explicit KR‐α method. This paper reviews the formulation of the KR‐α method and presents an efficient implementation for RTHS. Using the method, RTHS of a three‐story 0.6‐scale prototype steel building with nonlinear elastomeric dampers are conducted with a ground motion scaled to the design basis and maximum considered earthquake hazard levels. The results show that controllable numerical energy dissipation can significantly eliminate spurious participation of higher modes and produce exceptional RTHS results.
Keywords: Earthquake, RTHS, Nonlinear, Algorithms
Authors: Selim Günay; and Khalid M. Mosalam
DOI: 10.1002/eqe.2477
Abstract: This paper presents the implementation of Three Variable Control (TVC), an advanced control method, to the existing hybrid simulation (HS) system at the University of California, Berkeley. Motivation, background, and implementation of the TVC are explained together with modifications in the existing HS system. An application, which consists of the real‐time HS of electrical disconnect switches on a shaking table configuration, demonstrates successful implementation of the TVC. The presented application also covers other HS‐related features, namely employment of a three‐dimensional analytical substructure, real‐time HS‐compatible operator‐splitting integration method, and an efficient equation solver for faster computations.
Keywords: Earthquake, RTHS, Experimental
Authors: Matthew R. Eatherton; and Jerome F. Hajjar
DOI: 10.1002/eqe.2419
Abstract: The self‐centering rocking steel frame is a seismic force resisting system in which a gap is allowed to form between a concentrically braced steel frame and the foundation. Downward vertical force applied to the rocking frame by post‐tensioning acts to close the uplifting gap and thus produces a restoring force. A key feature of the system is replaceable energy‐dissipating devices that act as structural fuses by producing high initial system stiffness and then yielding to dissipate energy from the input loading and protect the remaining portions of the structure from damage. In this research, a series of large‐scale hybrid simulation tests were performed to investigate the seismic performance of the self‐centering rocking steel frame and in particular, the ability of the controlled rocking system to self‐center the entire building. The hybrid simulation experiments were conducted in conjunction with computational modules, one that simulated the destabilizing P‐Δ effect and another module that simulated the hysteretic behavior of the rest of the building including simple composite steel/concrete shear beam‐to‐column connections and partition walls. These tests complement a series of quasi‐static cyclic and dynamic shake table tests that have been conducted on this system in prior work. The hybrid simulation tests validated the expected seismic performance as the system was subjected to ground motions in excess of the maximum considered earthquake, produced virtually no residual drift after every ground motion, did not produce inelasticity in the steel frame or post‐tensioning, and concentrated the inelasticity in fuse elements that were easily replaced.
Keywords: Earthquake, Hybrid Simulation, Large Scale, Experimental
Authors: Selim Günay; and Khalid M. Mosalam
DOI: 10.1002/eqe.2394
Abstract: This paper presents the results of a parametric study that consists of real‐time hybrid simulation tests of electrical insulator posts on a smart shaking table. A companion paper presents the details of the development and validation of the real‐time hybrid simulation system used for conducting the tests of this parametric study. The purpose of the parametric study presented in this paper is to evaluate the effect of support structure damping and stiffness on the response of disconnect switches with two different insulator materials, namely porcelain and polymer insulator posts. Various global and local response parameters including accelerations, forces, displacements, and strains are considered in this evaluation. The data obtained from the conducted tests show that the maximum insulator response corresponds to the case where the support structure frequency is close to the insulator frequency. An incorporated evaluation of all the response parameters indicates that the stiff support structures constitute the most suitable configuration for both material types of the tested insulator posts. It is also observed that support structure damping has an effect on the response of both insulator types. However, this effect is secondary compared with the effect of support structure stiffness.
Keywords: Earthquake, RTHS
Authors: Khalid M. Mosalam; and Selim Günay
DOI: 10.1002/eqe.2395
Abstract: This paper presents the development and validation of a real‐time hybrid simulation (RTHS) system for efficient dynamic testing of high voltage electrical vertical‐break disconnect switches. The RTHS system consists of the computational model of the support structure, the physical model of the insulator post, a small shaking table, a state‐of‐the‐art controller, a data acquisition system and a digital signal processor. Explicit Newmark method is adopted for the numerical integration of the governing equations of motion of the hybrid structure, which consists of an insulator post (experimental substructure) and a spring‐mass‐dashpot system representing the support structure (analytical substructure). Two of the unique features of the developed RTHS system are the application of an efficient feed‐forward error compensation scheme and the ability to use integration time steps as small as 1 ms. After the development stage, proper implementation of the algorithm and robustness of the measurements used in the calculations are verified. The developed RTHS system is further validated by comparing the RTHS test results with those from a conventional shaking table test. A companion paper presents and discusses a parametric study for a variety of geometrical and material configurations of these switches using the developed RTHS system.
Keywords: Earthquake, RTHS, Algorithms, Experimental
Authors: M. Javad Hashemi; Armin Masroor; and Gilberto Mosqueda
DOI: 10.1002/eqe.2350
Abstract: Hybrid simulation combines numerical and experimental methods for cost‐effective, large‐scale testing of structures under simulated earthquake loading. Structural system level response can be obtained by expressing the equation of motion for the combined experimental and numerical substructures, and solved using time‐stepping integration similar to pure numerical simulations. It is often assumed that a reliable model exists for the numerical substructures while the experimental substructures correspond to parts of the structure that are difficult to model. A wealth of data becomes available during the simulation from the measured experiment response that can be used to improve upon the numerical models, particularly if a component with similar structural configuration and material properties is being tested and subjected to a comparable load pattern. To take advantage of experimental measurements, a new hybrid test framework is proposed with an updating scheme to update the initial modeling parameters of the numerical model based on the instantaneously‐measured response of the experimental substructures as the test progresses. Numerical simulations are first conducted to evaluate key algorithms for the selection and calibration of modeling parameters that can be updated. The framework is then expanded to conduct actual hybrid simulations of a structural frame model including a physical substructure in the laboratory and a numerical substructure that is updated during the tests. The effectiveness of the proposed framework is demonstrated for a simple frame structure but is extendable to more complex structural behavior and models.
Keywords: Earthquake, Hybrid Simulation, Model Updating, Algorithms, Experimental
Authors: Yunbyeong Chae; Karim Kazemibidokhti; and James M. Ricles
DOI: 10.1002/eqe.2294
Abstract: Hydraulic actuators are typically used in a real‐time hybrid simulation to impose displacements to a test structure (also known as the experimental substructure). It is imperative that good actuator control is achieved in the real‐time hybrid simulation to minimize actuator delay that leads to incorrect simulation results. The inherent nonlinearity of an actuator as well as any nonlinear response of the experimental substructure can result in an amplitude‐dependent behavior of the servo‐hydraulic system, making it challenging to accurately control the actuator. To achieve improved control of a servo‐hydraulic system with nonlinearities, an adaptive actuator compensation scheme called the adaptive time series (ATS) compensator is developed. The ATS compensator continuously updates the coefficients of the system transfer function during a real‐time hybrid simulation using online real‐time linear regression analysis. Unlike most existing adaptive methods, the system identification procedure of the ATS compensator does not involve user‐defined adaptive gains. Through the online updating of the coefficients of the system transfer function, the ATS compensator can effectively account for the nonlinearity of the combined system, resulting in improved accuracy in actuator control. A comparison of the performance of the ATS compensator with existing linearized compensation methods shows superior results for the ATS compensator for cases involving actuator motions with predefined actuator displacement histories as well as real‐time hybrid simulations.
Keywords: RTHS, Nonlinear, Experimental
Authors: Victor Saouma; Dae‐Hung Kang; and Gary Haussmann
DOI: 10.1002/eqe.1134
Abstract: The essence of real time hybrid simulation (RTHS) is the reliance on a physical test (virtual finite element) in support of a numerical simulation, which is unable to properly simulate it numerically. Hence, the computational support for a hybrid simulation is of paramount importance, and one with anything less than a state of the art computational support may defeat the purpose of such an endeavor. A critical, yet often ignored, component of RTHS is precisely the computational engine, which unfortunately has been a bottleneck for realistic studies. Most researches have focused on either the control or on the communication (mostly in distributed, non‐real time hybrid simulation) leaving the third leg of RTHS (computation) ignored and limited to the simulation of simple models (small number of degrees of freedom and limited nonlinearities). This paper details the development of a specialized software written explicitly to perform, single site, hybrid simulation ranging from pseudo‐dynamic to hard real time ones. Solution strategy, implementation details, and actual applications are reported.
Keywords: Hybrid Simulation, Nonlinear
Authors: Cheng Chen; and James M. Ricles
DOI: 10.1002/eqe.1144
Abstract: Real‐time hybrid simulation provides a viable method to experimentally evaluate the performance of structural systems subjected to earthquakes. The structural system is divided into substructures, where part of the system is modeled by experimental substructures, whereas the remaining part is modeled analytically. The displacements in a real‐time hybrid simulation are imposed by servo‐hydraulic actuators to the experimental substructures. Actuator delay compensation has been shown by numerous researchers to vitally achieve reliable real‐time hybrid simulation results. Several studies have been performed on servo‐hydraulic actuator delay compensation involving single experimental substructure with single actuator. Research on real‐time hybrid simulation involving multiple experimental substructures, however, is limited. The effect of actuator delay during a real‐time hybrid simulation with multiple experimental substructures presents challenges. The restoring forces from experimental substructures may be coupled to two or more degrees of freedom (DOF) of the structural system, and the delay in each actuator must be adequately compensated. This paper first presents a stability analysis of actuator delay for real‐time hybrid simulation of a multiple‐DOF linear elastic structure to illustrate the effect of coupled DOFs on the stability of the simulation. An adaptive compensation method then proposed for the stable and accurate control of multiple actuators for a real‐time hybrid simulation. Real‐time hybrid simulation of a two‐story four‐bay steel moment‐resisting frame with large‐scale magneto‐rheological dampers in passive‐on mode subjected to the design basis earthquake is used to experimentally demonstrate the effectiveness of the compensation method in minimizing actuator delay in multiple experimental substructures.
Keywords: Earthquake, RTHS, Large Scale, Experimental
Authors: Safwan Al-Subaihawi; Chinmoy Kolay; Thomas Marullo; James M. Ricles; and Spencer E. Quiel
DOI: 10.1016/j.engstruct.2019.110044
Abstract: This study examines the ability of damping devices placed between outrigger trusses and perimeter columns to mitigate dynamic vibrations in a tall building structure. The implementation of this approach to mitigate wind-induced vibrations for a 40-story building is assessed via a series of real-time hybrid simulations (RTHS), in which a numerical model of the complete building actively interfaces with physical dampers in the laboratory via actuators. In a RTHS, the overall structure is divided into analytical and experimental substructures, where the latter is challenging to model numerically and therefore evaluated in the laboratory as the experimental substructure. The experimental substructure for the RTHS in this study includes two full-scale nonlinear viscous dampers, and the rest of the building is modelled numerically as the analytical substructure. The coupling between the experimental and the analytical substructures is achieved in real time by enforcing compatibility and equilibrium between the two substructures during a simulation. Results of the RTHS show the feasibility of reducing the root mean square (RMS) and maximum wind-induced roof accelerations by up to 43% and 37%, respectively, when the building is subjected to a 700-year mean recurrence interval (MRI) storm with a 177 km/h basic wind speed. The stiffness of the members in the damper force path and the number of dampers play a major rule in controlling the wind induced vibrations. The results show that the as-built outrigger truss and column members require additional stiffening in order to maximize the benefit of adding the dampers to the building. There is a limit to the number of dampers that can be used beyond which minimal benefit is gained towards improving the performance of the building. RTHS are also used to estimate the equivalent viscous damping of the building with the outrigger damping system, which is found to be 8.7% of critical damping for the 1st mode of vibration.
Keywords: Wind, RTHS, Large Scale, Experimental
Authors: Amirali Najafi; Gaston A. Fermandois; and Billie F. Spencer Jr.
DOI: 10.1016/j.engstruct.2020.110868
Abstract: Real-time hybrid simulation (RTHS) is a cost and space efficient alternative to shake table testing for seismic assessment of structural systems. In this method, complete structural systems are partitioned into numerical and physical components and tested at real earthquake velocities. Well-understood components of the structure are modeled in finite-element numerical models. Meanwhile, the physical substructure, which often contains the highly nonlinear and numerically burdensome components is fabricated and tested in a laboratory facility. Testing at real earthquake velocities is useful to obtain nonlinear rate-dependent material behaviors. Realistic reproduction of seismic conditions for structural assessment has required researchers to develop multi-axial RTHS capabilities. In such developments, multiple actuators are arranged at the boundary condition with the physical specimen to impose realistic displacements and rotations. But, varying degrees of dynamic coupling exist between the actuators in multi-axial boundary conditions. Controllers and kinematic transformations are developed for the tracking action of the actuators to compensate for the amplitude and phase discrepancies between target and measured displacement signals, otherwise stability issues are likely to result. In this paper, a multi-axial framework is introduced for RTHS testing, using a Load and Boundary Condition Box (LBCB) at the University of Illinois at Urbana-Champaign. The previously developed multi-axial RTHS framework for the LBCBs compensates for actuator dynamics in Cartesian coordinates; this approach lacked stability robustness when testing stiff specimens. The distinguishing feature of the proposed framework is that tracking compensation is executed in the actuator coordinates. The differences between the previous and proposed multi-axial RTHS frameworks are explored in detail herein. This paper presents the components of the framework and the describes a six-degree-of-freedom moment frame RTHS experiment. Finally, experimental results are discussed and directions for future research efforts are considered.
Keywords: Earthquake, RTHS, Algorithms, Experimental, Controller Design
Authors: Amirali Najafi; and Billie F. Spencer Jr.
DOI: 10.22055/JACM.2020.32584.2039
Abstract: Hybrid simulation (HS) is a cost-effective alternative to shake table testing for evaluating the seismic performance of structures. HS structures are partitioned into linked physical and numerical substructures, with actuators and sensors providing the means for the interaction. Load application in conventional HS is conducted at slow rates and is sufficient when material rate-effects are negligible. Real-time hybrid simulation (RTHS) is a variation of the HS method, where no time-scaling is applied. Despite the recent strides made in RTHS research, the body of literature validating the performance of RTHS, compared to shake table testing, remains limited. In the few available studies, the tested structures and assemblies are linear or modestly nonlinear, and artificial damping is added to the numerical substructure to ensure convergence and stable execution of the simulation. The objective of this study is the validation of a recently proposed model-based RTHS framework, focusing on lightly-damped and highly-nonlinear structural systems; such structures are particularly challenging to consider using RTHS. The boundary condition in the RTHS tests are enforced via displacement and acceleration tracking. The modified Model-Based Control (mMBC) compensator is employed for the tracking action. A two-story steel frame structure with a roof-level track nonlinear energy sink (NES) device is selected due to its light damping, high nonlinearity, and repeatability. The complete structure is first tested on a shaking table, and then substructured and tested via the RTHS method. The model-based RTHS approach is shown to perform similar to the shake table method, even for lightly-damped and highly-nonlinear structures.
Keywords: Earthquake, RTHS, Algorithms, Experimental
Authors: Zhenyun Tang; Matt Dietz; and Yue Hong Zhenbao Li
DOI: 10.1002/stc.2611
Abstract: Real‐time dynamic hybrid testing (RTDHT) is a state‐of‐the‐art experimental technique for evaluating the performance of a structural system subjected to time‐varying loads. Because of the superiority of shaking table for testing rate‐dependent and inertial effect existing in structural system, shaking table‐based RTDHT is an important branch in RTDHT family, in which shaking table is used to impose inertial forces on physical substructure. Owing to the mass of the seismic platform, shaking table has a relatively narrow testing bandwidth akin to a stand‐alone actuator RTDHT system. Furthermore, structure–table interaction confines the physical substructure to a very small mass and linear stage, such that shaking table‐based RTDHT is unable to test the structural performance with consideration of high frequency input or non‐linearity using large‐scale physical substructure. Actually, this is why we develop RTDHT. In this work, a control strategy named full state control via simulation (FSCS) was proposed to extend the testing capacity of shaking table‐based RTDHT. The efficiency of FSCS‐controlled RTDHT for testing high frequency and non‐linear structural performance was verified by a small‐ and large‐scale shaking table‐based RTDHT, respectively.
Keywords: Earthquake, RTHS, Nonlinear, Large Scale, Experimental
Authors: Ryuta Enokida
DOI: 10.1002/stc.2497
Abstract: This study examines two basic substructuring schemes for shake table tests where the dynamics of the table is significantly affected by a specimen. The hybrid simulation (HS) scheme, commonly adopted in substructuring experiments, directly uses the output of a numerical substructure as an input signal to a physical substructure. The dynamical substructuring system (DSS) scheme, developed long after HS, uses feedforward and feedback controllers to minimise the control error produced by the outputs of numerical and physical substructures. Before examining these two schemes, this study introduces a systematic formulation for dividing a multi‐degree‐of‐freedom emulate system into a numerical substructure and a physical substructure with a shake table. Then, controller designs for HS and DSS are discussed for the substructures. The two schemes with basic control approaches were numerically examined through substructuring tests for a linear 3DOF emulate system. DSS with stability was powerful even under a control condition with a pure time delay and inaccurate estimation of the table dynamics, whereas these factors degraded the HS performance. In additional simulations in which nonlinear characteristics were considered, the performance of DSS (HS) was degraded mainly by the nonlinear (inaccurate estimation of the table dynamics). It was found that the stability of substructures with nonlinear characteristics could be roughly assessed by the Nyquist stability criterion. These simulations with/without nonlinear characteristics clarified the performances of the HS and DSS schemes through basic control approaches and stability analysis under practical conditions.
Keywords: Earthquake, Hybrid Simulation, Nonlinear, Experimental, Controller Design
Authors: Mohit Verma; M. V. Sivaselvan; and J. Rajasankar
DOI: 10.1002/stc.2402
Abstract: This paper presents a new strategy for dynamic substructuring in which an actuator/shaker is not viewed as a tracking device, but rather as a dynamic system whose impedance is to match that of a virtual substructure. The strategy also decouples control design from the physical substructure. In this paper, such control design is approached from an optimization viewpoint. The main contributions are (a) single and multi‐objective optimal impedance matching design of dynamic substructuring controllers using linear matrix inequalities, (b) experimental validation, particularly using a lightly damped physical substructure (which poses significant stability challenges using conventional approaches), (c) use of an electromagnetic actuator as an active mass driver to represent virtual substructures, (d) use of not only linear single and multi‐degree of freedom but also nonlinear virtual substructures, and (e) two ways of applying earthquake excitation to the substructured system—by means of a shake table at the base or using an active mass driver at the top. Controllers designed using this approach are easy to implement and result in stable and accurate dynamic substructuring. Source code for control design using the impedance matching approach is included as online supplemental material with this paper.
Keywords: Earthquake, Hybrid Simulation, Nonlinear, Experimental, Controller Design
Authors: Bo Fu; Huanjun Jiang; and Tao Wu
DOI: 10.1002/stc.2295
Abstract: In order to evaluate the effectiveness of particle dampers (PDs) on seismic response reduction of structures, a series of substructure shake table tests have been conducted. A new family of explicit model‐based integration algorithms is used to develop the substructure shake table testing (SSTT) method. To implement the SSTT method, a testing system on the basis of the Quanser shake table II is constructed. The effectiveness and accuracy of the proposed SSTT method and the testing system are verified by comparing the results of complete structure shake table tests and the corresponding substructure shake table tests. Mass ratio, which is defined as the ratio of the damper mass to the structural mass and structural damping ratio are taken as two main parameters in the parametric analyses. Twelve cases of PDs, which are categorized into three patterns, with different materials, sizes, and amounts of particles are selected as the experimental substructures. The substructure shake table test results indicate that the overall seismic response reduction effects of three different types of PDs are very close with same mass ratio. Two seismic response reduction ratios in terms of reducing peak and root‐mean‐square relative structural displacements are defined to quantify the seismic response reduction effects of the dampers. It can be concluded from the experimental studies that both seismic response reduction ratios increase as the mass ratio increases and decreases as the structural damping ratio increases.
Keywords: Earthquake, RTHS, Algorithms, Experimental
Authors: Yuanfeng Duan; Junjie Tao; Hongmei Zhang; Sumei Wang; and Chungbang Yun
DOI: 10.1002/stc.2277
Abstract: The numerical substructure of a real‐time hybrid simulation (RTHS) has been considerably simplified through condensation methods to relieve the burden incurred by computation. However, this simplification severely limits the application of RTHS to structures whose numerical parts are complex and require a large number of degrees of freedom (DOFs) to model. Thus, in this study, a vector form intrinsic finite element (VFIFE) analysis is introduced to RTHS with numerical substructures containing a large number of DOFs. A field programmable gate array (FPGA) is also employed to speed‐up the numerical simulation of the VFIFE through parallel computing in RTHS. The characteristics of this parallel RTHS platform using VFIFE and FPGA are discussed in detail in this paper. A simple RTHS was carried out to verify the feasibility of this new platform, followed by a complex virtual RTHS to show its powerful computational capability.
Keywords: RTHS, Parallel RT Execution
Authors: Maedeh Zakersalehi; Abbas Ali Tasnimi; and Mehdi Ahmadizadeh
DOI: 10.1002/stc.2283
Abstract: One of the main challenges of hybrid simulation is developing integration methods that not only provide accurate and stable results but also are compatible with the hybrid simulation circumstances. This paper presents a novel enhanced integration technique for hybrid simulation termed “modified operator splitting” (MOS) method. The main aim of the MOS technique is to improve the precision of the operator splitting (OS) method by reducing the corrector step length, where initial stiffness is utilized instead of actual stiffness. For this purpose, a new algorithm is proposed, which makes a more precise estimation of the predictor displacement; thus minimizes the effect of the corrective procedure. As a result, a higher percentage of the restoring force is based on actual experimental behavior rather than being approximated, which finally leads to a very precise and reliable integration method, especially for nonlinear hybrid simulations. Performance of the MOS method is evaluated by the following: (a) Analytical studies, (b) numerical simulations, and (c) hybrid simulation. The accuracy analysis for a wide range of structures and ductility levels demonstrates the superior precision of MOS over OS, especially for severe nonlinearities and larger Δt/T0. In terms of stability, it is shown that for practical applications of civil engineering problems, MOS provides stable results. Furthermore, the application of MOS to hybrid simulation not only again verifies its higher precision over OS, but also shows that MOS minimizes the accumulation of errors during the test; the characteristic that is desirable for a method applied to feedback systems such as hybrid simulation.
Keywords: Hybrid Simulation, Nonlinear, Algorithms, Experimental
Authors: Fei Zhu; Jin‐Ting Wang; Feng Jin; Li‐Qiao Lu; Yao Gui; and Meng‐Xia Zhou
DOI: 10.1002/stc.1962
Abstract: The use of tuned liquid dampers (TLDs) is an effective passive control technique to suppress structural vibration under wind and seismic loads. This paper investigates the size effect of TLDs on control efficiency. Given the advantages of real‐time hybrid simulation, two issues affecting the control performance of TLD are addressed: (a) the geometric size and (b) the experimental model scale. A series of real‐time hybrid simulations is performed, in which TLD devices with various sizes (including full‐scale and small‐scale) are experimentally modeled as physical substructures; the controlled structures are numerically simulated as numerical substructures. Results demonstrate that TLD performance is size dependent; a shallow liquid in TLD with lower relative liquid depth may be more efficient for both peak and root‐mean‐square response control. Scaled TLD models that are usually used in conventional shaking table tests generally overestimate the control performance of prototype TLD devices, indicating that full‐scale TLD experiments should be pursued to ensure proper performance evaluation.
Keywords: Earthquake, Wind, RTHS, Experimental
Authors: Z. Sun; G. Ou; S. J. Dyke; and C. Lu
DOI: 10.1002/stc.1929
Abstract: Structural control systems based on wireless sensors offer a convenient, flexible and cost‐effective alternative to their wired counterparts. Although wireless control systems (WCSs) have several attractive features, some challenges do remain related to the persistent presence of network‐induced time delays, and potential for sensor data losses and in extreme cases, sensor failures. The consequences of these challenges should be investigated, and solutions should be developed to achieve highly effective and robust control systems. The availability of such solutions will also encourage the adoption of WCSs in real structures. Here, an estimator switching method intended to minimize the influence of potential faults is developed and validated for WCSs. In this method, the switching gains are pre‐calculated to enable real‐time implementation. The proposed method is verified through numerical simulations of a seismically excited, three‐story structure considering various sensor data loss and sensor failure scenarios. The robustness of this estimation method in the presence of measurement noise and modeling uncertainty is also investigated. In addition, the estimation switching method is incorporated into a closed‐loop WCS in experiment. The results demonstrate the effectiveness of the proposed state estimation method in mitigating the impact of sensor data loss and sensor failure.
Keywords: Earthquake, RTHS, UQ, Experimental
Authors: Jin‐Ting Wang; Yao Gui; Fei Zhu; Feng Jin; and Meng‐Xia Zhou
DOI: 10.1002/stc.1822
Abstract: As a low cost and maintenance energy‐absorbing device, tuned liquid damper (TLD) is being widely used to suppress structural vibration. In this paper, the real‐time hybrid simulation (RTHS) is employed to investigate the performance of TLD for controlling seismic responses of actual multi‐story structures, where the TLD is experimentally modeled as physical substructure and the multi‐story structure is numerically simulated as numerical substructure. Taking advantage of RTHS technique, a methodology for achieving full‐scale TLD experiments is developed through suitable similarity design; a new interaction force measurement method and a new dual explicit algorithm are embedded into RTHS system to enhance simulation capability. First, the seismic response of a two‐story structure installed with TLD is analyzed by applying RTHS. Correspondingly, the pure shaking table test is performed to assess the accuracy of the RTHS. Then, the effectiveness of TLD for structures with various numbers of floors and different structural properties is tested through RTHS by varying the simulation model of the numerical substructure. Finally, the effects of mass ratio and structural damping ratio on a given TLD‐structure system are investigated.
Keywords: Earthquake, RTHS, Algorithms, Experimental
Authors: Yanhui Liu; Kevin Goorts; Ali Ashasi‐Sorkhabi; Oya Mercan; and Sriram Narasimhan
DOI: 10.1002/stc.1798
Abstract: Real‐time hybrid simulation (RTHS) combines experimental testing with numerical simulation. It provides an alternative method to evaluate the performance of structures subjected to dynamic loading such as earthquake or wind. During RTHS, a numerical integration algorithm is employed to directly solve the equation of motion and generate command displacements for the experimental test structure online. This paper presents an improved explicit numerical integration method for RTHS based on discrete state space formulation. The improved integration method utilizes an extrapolation‐based prediction procedure for command displacement by applying a zero‐order hold. The predicted command displacement is then used to compute the final command displacement by applying a first‐order hold. Both the stability and the accuracy of the proposed integration method are investigated using control theory and numerical and experimental simulations. The proposed method demonstrates improved performance compared with other integration methods. The robustness and feasibility of the proposed method were verified through experimental RTHS on two different computational platforms including a National Instruments system and a dSPACE embedded controller. The proposed method may also be implemented on other platforms containing an xPC target and MATLAB environment. By placing the algorithm on the dSPACE system, any dynamically rated actuator with a controller that can receive analog signal may be used for RTHS.
Keywords: Earthquake, Wind, RTHS, Theory, Algorithms, Experimental
Authors: Hadi Moosavi; Reza Mirza Hessabi; and Oya Mercan
DOI: 10.1002/stc.1731
Abstract: In order to investigate the dynamic behavior of complex structural systems experimental testing is indispensable and real‐time pseudodynamic (PSD) and real‐time hybrid simulation (RTHS) are versatile testing methods to address this need. Accurate control of hydraulic actuators is essential for the accuracy and stability of these methods. This paper introduces a nonlinear state‐space controller to control hydraulic actuators under displacement control, specifically for real‐time testing applications. The proposed control design process uses the nonlinear state‐space model of the system, and utilizes state feedback linearization through a transformation of the state variables. As such, it can efficiently handle the nonlinearities associated with the servo‐hydraulic system and the test structure. Comparisons of numerical simulation results for linear state‐space and nonlinear state‐space controllers are provided. The improved tracking performance of the proposed controller will contribute to more accurate real‐time test results, which in turn will enable a more accurate assessment of dynamic characteristics of complex structural systems.
Keywords: RTHS, Nonlinear, Controller Design
Authors: Jia‐Ying Tu; Chih‐Ying Chen; and Wei‐De Hsiao
DOI: 10.1002/stc.1685
Abstract: Dynamically substructured system (DSS) techniques separate critical components of a complete structural system to be physically tested in full size; the remaining linear subsystems are tested numerically. Successful and robust DSS tests rely on a high‐quality controller to cope with undesired disturbances surrounding the real‐time environment and thus ensure synchronised responses of the numerical and physical substructure outputs. Three DSS control systems are compared in this paper, which use dynamics‐based ordinary differential equations or geometry‐based delay differential equations to model the systems. Even though the control designs are not new, a series of new experimental and analytical results capture the essence of DSS control problems in a simple way, showing that (i) reliable DSS tests depend on well‐defined dynamics and numerical computational accuracy in the control design, (ii) dynamics‐based methods lay a relatively transparent and systematic foundation for deeper investigation into robustness issues and (iii) an understanding of potential and fundamental real‐time difficulties is important in order to give hints for accurate modelling, control redesign and quality improvement.
Keywords: RTHS, Experimental, Controller Design
Authors: Huaibing Xu; Chunwei Zhang; Hui Li; and Jinping Ou
DOI: 10.1002/stc.1585
Abstract: Small‐scale models have been commonly utilized in testing of performance of active mass driver (AMD) control systems. The utmost reason is that physical testing of AMD system at full scale is usually too expensive to afford, as well as hard to implement on site. With reference to the real‐time hybrid simulation technology, a real‐time AMD subsystem testing method is proposed in this paper. In this method, the entire system is composed of AMD as physical subsystem and target structure as numerical subsystem. The physical test is conducted on AMD subsystem, whereas the numerical simulation is carried out on the structure subsystem. Meanwhile, the real‐time data are being communicated between these two subsystems. This method is then applied to the performance validation of a novel AMD control system, which is driven by a linear motor. In the test, a benchmark three‐storey frame structure is employed as the numerical subsystem, and earthquake excitations are used as the external input. On the basis of a series of tests, both the time history and the statistical criteria show that the results of AMD subsystem and structure subsystem obtained in the real‐time AMD subsystem test agree well with the simulation results. Furthermore, all the test results show good repeatability. Therefore, the feasibility and reliability of the proposed real‐time AMD subsystem testing approach for performance validation of AMD subsystem has been demonstrated. Such kind of experimental method is efficient in terms of reducing cost associated with performance validation of large‐scale active control systems prior to the implementation.
Keywords: Earthquake, RTHS, Experimental, Case Study, Benchmark
Authors: Shohei Yoshida; Hideo Fujitani; Yoichi Mukai; and Mai Ito
DOI: 10.1002/2475-8876.12034
Abstract: This study proposes a real‐time hybrid simulation method for semi‐active control using a shaking table. The method can be used for simulating a mid‐story isolated building. This simulation system uses a test specimen for the upper structure, a semi‐active damper that is installed in the base isolation layer on the shaking table, and a lumped mass system for a lower structure for the computer simulation. A rotary inertia mass damper that contains magnetorheological fluid is used in the semi‐active control. The semi‐active control cannot avoid a control time lag. This time lag is estimated by assuming a first‐order lag system. The experimental and analytical results considering a control time lag are compared in this study. The validity of the real‐time hybrid simulation is verified.
Keywords: Earthquake, RTHS, Experimental, Case Study
Authors: Estacio Pereira, Ph.D.; SangUk Han, Ph.D., A.M.ASCE; and Simaan AbouRizk, Ph.D., P.Eng., M.ASCE
DOI: 10.1061/(ASCE)CP.1943-5487.0000792
Abstract: Assessment models capable of determining the impact of various safety-related scenarios on safety performance have been developed and described in the literature. In spite of this, however, practical implementation of this work remains limited due to the inability of these models to consider the dynamic nature of construction processes. This paper proposes a conceptual approach, which combines case-based reasoning and simulation modeling, to account for the dynamic nature of construction projects by allowing the assessment of safety performance over time. In the proposed approach, safety scenarios predicted by the simulation model are compared with historical cases within a database to assess safety performance. Then, the simulation model, which combines discrete and continuous simulation to replicate the life cycle of the project, is used to update safety-related measures at specified time intervals. This integrated approach was applied in practice to predict how resource allocation and safety policies of a construction project could affect safety performance and was found capable of assisting managers with the proactive development of strategies designed to improve safety performance.
Keywords: Hybrid Simulation
Authors: Gregory Bunting; Arun Prakash, A.M.ASCE; Shirley Dyke; and Amin Maghareh, A.M.ASCE
DOI: 10.1061/(ASCE)CP.1943-5487.0000577
Abstract: The multi-time-step method of time integration for problems in structural dynamics allows one to decompose the problem domain into small subdomains and use different time steps within each subdomain to reduce the computational cost of solving such problems. However, the number of possible decompositions and their associated time steps for a given model is huge and grows exponentially with the number of elements. To find an optimal decomposition that minimizes error in the solution while maintaining a bound on the computational cost is challenging. In this work, existing multi-time-step methods are used and, for the first time, a systematic approach for traversing the space of possible decompositions to characterize the nature of how solution errors and computational costs vary for different decompositions is devised. Through numerical examples for three different types of structures, trusses, frames, and continuum solid bodies, it is shown that the characteristics of these error and cost functions are similar across problem types. Based on these functions, optimal decompositions that maximize the benefits of multi-time-step methods are identified.
Keywords: Hybrid Simulation
Authors: Limao Zhang; Xianguo Wu; and Miroslaw J. Skibniewski, M.ASCE
DOI: 10.1061/(ASCE)CP.1943-5487.0000542
Abstract: This paper develops a hybrid simulation approach that integrates a dynamic default tree (DFT) and discrete-time Bayesian network (DTBN) to support tunnel boring machine (TBM) performance prediction and diagnosis. A causal network model consisting of 20 nodes is built to simulate shield cutter head failure over time during the TBM operation. A total of three indicators, namely, T10, T20, and mean time to failure (MTTF), are proposed to transfer the complicated probability distribution into a specific and useful number to explicitly measure the performance level of system unreliability. One of the tunneling projects recently completed in the Wuhan metro system in China has been selected as a case study to verify the applicability of the developed approach. The results indicate that the developed approach is capable of performing not only a feedforward analysis for the estimation of the TBM performance, but also feedback analysis, given that a low performance or failure is observed. This approach provides a powerful potential solution to modeling and analyzing various kinds of system component behaviors and interactions in a complex project environment.
Keywords: Hybrid Simulation, Case Study
Authors: Ignacio Lamata Martinez; Ferran Obon Santacana; Martin S. Williams; Anthony Blakeborough; and Uwe E. Dorka
DOI: 10.1061/(ASCE)CP.1943-5487.0000455
Abstract: Distributed hybrid simulation is an approach to large-scale testing in which the system under test is split into several sub-structures which are tested or simulated in different locations. Data are passed between the sub-structures at each timestep so as to ensure that the distributed experiment realistically simulates the full system under test. This approach optimises the use of resources at different locations to achieve a more representative experiment. While different software to conduct distributed simulations exists, there are no standards and specifications to organise and plan the experiments, and as a result the different systems lack inter-operability. To address these issues, we have developed a high-level specification called Celestina, which provides a framework for conducting a distributed experiment. Celestina specifies the services to be implemented, under three main headings of networking, definition and execution, and supports the data exchange during a simulation. It does not force any particular implementation or method of data exchange. This paper summarises the Celestina specification and describes one implementation. Lastly, a validation experiment is presented, involving distributed numerical simulations of an earlier local hybrid experiment, in which Celestina controls the experiment planning and data exchange effectively and with minimal computational overhead.
Keywords: Earthquake, Hybrid Simulation, Experimental
Authors: Carol C. Menassa, A.M.ASCE; Vineet R. Kamat, A.M.ASCE; SangHyun Lee, A.M.ASCE; Elie Azar, S.M.ASCE; Chen Feng, S.M.ASCE; and Kyle Anderson, S.M.ASCE
DOI: 10.1061/(ASCE)CP.1943-5487.0000299
Abstract: In this paper, a conceptual framework that couples energy modeling with occupancy characteristics and energy use data is developed and tested to achieve two main objectives: (1) couple distinct and spatially distributed simulation models and synchronize their data exchange, and (2) illustrate the coupled model behavior through a hypothetical case study example of a building. This conceptual framework is developed using a distributed computing environment based on the principles defined in the high-level architecture (HLA). Thus, individual simulation models and control interfaces developed for their own purpose, called federates, are composed and coupled together in an HLA-compliant federation that allows federates to continuously communicate with one another and exchange relevant information at each time step to achieve the global objective of reducing the building’s energy use. A case study example of a typical commercial building illustrates how the model coordinates data synchronization and transfer between federates, which run simultaneously in a distributed fashion. This example tests the effect of energy intervention scenarios, namely, feedback frequency to building occupants on the building’s energy use, and it illustrates the potential application of the framework to study energy interventions in buildings.
Keywords: Case Study
Authors: Liang Huang; Cheng Chen, M.ASCE; Tong Guo, M.ASCE; and Xiaoshu Gao
DOI: 10.1061/(ASCE)EM.1943-7889.0001835
Abstract: Stability of real-time hybrid simulation (RTHS) has attracted considerable attention given that actuator delay might destabilize the real-time test, especially when the compensation is not sufficient. Previous research by the authors explored the stability of RTHS with time-varying delay, but the derived stability criteria are relatively conservative due to the application of the Lyapunov-Krasovskii (L-K) theory. For overcoming such defect and pursuing a more accurate stability analysis, this study introduces a delay decomposition approach to reduce the conservatism of matrix inequality with convexity property. For both constant and time-varying delay systems, the delay decomposition approach performed remarkably in stability analysis. Moreover, with the increase in number of decomposition, this approach can further improve the accuracy of analysis results and reduce its conservatism; however, the computational efforts will rise rapidly. Computational simulation verified the effectiveness of the delay decomposition approach especially for the physical substructure involving a small stiffness ratio.
Keywords: RTHS, Theory
Authors: Nikolaos Tsokanas; David Wagg; and Bozidar Stojadinovic
DOI: 10.3389/fbuil.2020.00127
Abstract: Hybrid simulation is an efficient method to obtain the response of an emulated system subjected to dynamic excitation by combing loading-rate-sensitive numerical and physical substructures. In such simulations, the interfaces between physical and numerical substructures are usually implemented using transfer systems, i.e. an arrangement of actuators. To guarantee high fidelity of the simulation outcome, conducting hybrid simulation in hard real-time is required. Albeit attractive, real-time hybrid simulation comes with numerous challenges, such as the inherent dynamics of the transfer system used, along with communication interrupts between numerical and physical substructures, that introduce time delays to the overall hybrid model altering the dynamic response of the system under consideration. Hence, implementation of adequate control techniques to compensate for such delays is necessary. In this study, a novel control strategy is proposed for time delay compensation of actuator dynamics in hard real-time hybrid simulation applications. The method is based on designing a transfer system controller consisting of a robust model predictive controller along with a polynomial extrapolation algorithm and a Kalman filter. This paper presents a proposed tracking controller first, followed by two virtual real-time hybrid simulation parametric case studies, which serve to validate the performance and robustness of the novel control strategy. Real-time hybrid simulation using the proposed control scheme is demonstrated to be effective for structural performance assessment.
Keywords: Earthquake, RTHS, UQ, Nonlinear, Case Study, Transfer Systems, Controller Design
Authors: Chen, Pei-Ching
DOI: 10.12989/sss.2020.25.6.719
Abstract: Real-time hybrid simulation (RTHS) which combines physical experiment with numerical simulation is an advanced method to investigate dynamic responses of structures subjected to earthquake excitation. The desired displacement computed from the numerical substructure is applied to the experimental substructure by a servo-hydraulic actuator in real time. However, the magnitude decay and phase delay resulted from the dynamics of the servo-hydraulic system affect the accuracy and stability of a RTHS. In this study, a robust stability analysis procedure for a general single-degree-of-freedom structure is proposed which considers the uncertainty of servo-hydraulic system dynamics. For discussion purposes, the experimental substructure is a portion of the entire structure in terms of a ratio of stiffness, mass, and damping, respectively. The dynamics of the servo-hydraulic system is represented by a multiplicative uncertainty model which is based on a nominal system and a weight function. The nominal system can be obtained by conducting system identification prior to the RTHS. A first-order weight function formulation is proposed which needs to cover the worst possible uncertainty envelope over the frequency range of interest. Then, the Nyquist plot of the perturbed system is adopted to determine the robust stability margin of the RTHS. In addition, three common delay compensation methods are applied to the RTHS loop to investigate the effect of delay compensation on the robust stability. Numerical simulation and experimental validation results indicate that the proposed procedure is able to obtain a robust stability margin in terms of mass, damping, and stiffness ratio which provides a simple and conservative approach to assess the stability of a RTHS before it is conducted.
Keywords: Earthquake, RTHS, UQ, Experimental
Authors: M. Chen; T. Guo; C. Che; and W. Xu
DOI: 10.1007/s40799-020-00381-w
Abstract: Uncertainties in real-time hybrid simulation include structural parameters and ground motion. Uncertain parameters often do not follow common distribution types. Data-driven arbitrary polynomial chaos constructs optimal orthogonal polynomial basis based on the sample data without distribution assumption. In this study, the data-driven polynomial chaos is compared with other generalized polynomial chaos from the aspects of the rate of error convergence when applied for uncertainty quantification of real-time hybrid simulation. Moreover, uncertainties of ground motion are considered in the RTHS problem to represent the scenarios with more complex input variables. Different statistical indicators are utilized to evaluate the accuracy of the alternative model in comparison with the Monte Carlo simulation results. Compared with generalized polynomial chaos, the data-driven arbitrary polynomial chaos presents potential for uncertainty quantification of real-time hybrid simulation with approximate or better accuracy. Actuator delay in RTHS could change the sensitivity of model output to the random variables.
Keywords: RTHS, UQ
Authors: Zhen Wang; Xu, Guoshan; Li, Qiang; and Wu, Bin
DOI: 10.12989/sss.2020.25.5.569
Abstract: The identification of delays and delay compensation are critical problems in real-time hybrid simulations (RTHS). Conventional delay compensation methods are mostly based on the assumption of a constant delay. However, the system delay may vary during tests owing to the nonlinearity of the loading system and/or the behavioral variations of the specimen. To address this issue, this study proposes an adaptive delay compensation method based on a discrete model of the loading system. In particular, the parameters of this discrete model are identified and updated online with the least-squares method to represent a servo hydraulic loading system. Furthermore, based on this model, the system delays are compensated for by generating system commands using the desired displacements, achieved displacements, and previous displacement commands. This method is more general than the existing compensation methods because it can predict commands based on multiple displacement categories. Moreover, this method is straightforward and suitable for implementation on digital signal processing boards because it relies solely on the displacements rather than on velocity and/or acceleration data. The virtual and real RTHS results show that the proposed method exhibits satisfactory estimation smoothness and compensation accuracy. Furthermore, considering the measurement noise, the low-order parameter models of this method are more favorable than that the high-order parameter models.
Keywords: RTHS, Nonlinear
Authors: Wei Wei; Yong Yuan; Akira Igarashi; Hongping Zhu; and Kaitao Luo
DOI: 10.1016/j.conbuildmat.2020.119211
Abstract: Unfilled and carbon black filled natural rubber have attracted considerable attention and have been extensively used as a novel construction material in civil infrastructure applications because of their superior physical and mechanical properties. However, their mechanical behavior is highly nonlinear and further complicated by the significant sensitivity to the loading rate. In this paper, a generalized constitutive model was proposed to improve the description of rate-dependent mechanical behavior of unfilled and carbon black filled natural rubber. The proposed model consisted of a hyperelastic spring to characterize the equilibrium response and a Maxwell element to capture the rate dependency as well as link the overstress to the loading rate. Subsequently, the stress–strain response of both unfilled and filled natural rubber subjected to the cyclic shear loading with different strain rates was experimentally characterized, multi-step relaxation and cyclic shear tests were carried out to calibrate material parameters in the model. Afterwards, a nonlinear viscosity coefficient was derived to completely establish the proposed model and its three-dimensional function versus strain and strain rate was also obtained based on the experimental data. Finally, comparing numerical simulations with cyclic shear tests and real-time hybrid simulation tests, it was found that the simulated results were in good agreement with the test results, indicating the proposed model is capable to accurately describe the hyper-viscoelastic behavior of both unfilled and filled natural rubber under cyclic shear loading, which might become an appropriate choice to be used by researchers and engineers for civil structural applications.
Keywords: RTHS, Nonlinear, Experimental
Authors: Liang Huang; Cheng Chen; Menghui Chen; and Tong Guo
DOI: 10.1080/13632469.2019.1688735
Abstract: In a real time hybrid simulation (RTHS), the actuator delay might deviate experimental results, or even destabilize the real-time test. Currently, research is very limited on stability of multiple-degree-of-freedom (MDOF) structures with multiple delays. Using the Lyapunov-Krasovskii (L-K) method, this study proposes stability criteria for MDOF systems with multiple time-varying/constant delays, and derives a more accurate result. Application of criteria shows that the stability of time-varying delay system is smaller than the corresponding constant delay system. With number of DOF and delay increasing, the criterion accuracy decreases slowly for constant delay system; meanwhile, the stability difference between constant- and time-varying- delay system increases gradually. Such difference is significant with small stiffness ratio of physical substructure.
Keywords: RTHS, Experimental
Authors: Tengfei Li; Lei Ma; Yan Sui; Mingzhou Su; and Yi Qiang
DOI: 10.1007/s10518-020-00798-z
Abstract: Soft real-time hybrid simulation (S-RTHS) is a novel seismic test method for structures. It combines pure finite element simulation with laboratory physical component tests, and can lead to a more realistic simulation of real-time effects of seismic action on specimens. Based on the OpenFresco test communication platform and an MTS electro-hydraulic servo loading system, a systematical study on the technological application of S-RTHS is presented in this paper. A single-story, single-span space steel frame was taken as a prototype, a column was taken as an experimental substructure, and the remaining part of the structure was taken as a numerical substructure to be simulated in OpenSEES. S-RTHS with bidirectional loading was performed, and the boundary conditions of the experimental substructure were simulated and analyzed. The results from the pure numerical simulations and S-RTHS were compared along with the responses from these simulations. The command displacement and feedback displacement of the system were discussed to verify the accuracy and stability of the S-RTHS. Finally, a comparison with the slow substructure hybrid simulation test results shows that the S-RTHS can better simulate the dynamic response of the experimental substructure.
Keywords: Earthquake, RTHS, Experimental
Authors: Ashkan Keivan; Ruiyang Zhang; Darioush Keivan; Brian M. Phillips; Masahiro Ikenaga; and Kohju Ikago
DOI: 10.1080/13632469.2019.1693444
Abstract: In this study, rate-independent linear damping (RILD) is proposed for the seismic protection of inter-story isolated structures. For practical applications, the RILD force is approximated using a causal algorithm and then tracked using semi-active control. Both numerical simulation and shake table real-time hybrid simulation (RTHS) are used to study a 14-story inter-story isolated structure. First, the causal approximation of RILD evaluated in RTHS is compared to numerical simulation. Second, the benefits of RILD for inter-story isolated structures are demonstrated as compared to conventional damping. RILD offers an attractive control alternative by restricting isolation layer displacements without amplifying accelerations.
Keywords: Earthquake, RTHS, Algorithms
Authors: Brian M. Phillips, A.M.ASCE; and Billie F. Spencer Jr., F.ASCE
DOI: 10.1061/(ASCE)ST.1943-541X.0000606
Abstract: Substructure hybrid simulation is a powerful, cost-effective alternative for testing structural systems, closely coupling numerical simulation and experimental testing to obtain the complete response of a structure. In this approach, well-understood components of the structure are modeled numerically, while the components of interest are tested physically. Generally, an arbitrary amount of time may be used to calculate and apply displacements at each step of the hybrid simulation. However, when the rate-dependent behavior of the physical specimen is important, real-time hybrid simulation (RTHS) must be used. Computation, communication, and servohydraulic actuator limitations cause delays and lags that lead to inaccuracies and potential instabilities in RTHS. This paper proposes a new model-based servohydraulic tracking control method including feedforward-feedback links to achieve accurate tracking of a desired displacement in real time. The efficacy of the proposed approach is demonstrated through RTHS for a single-degree-of-freedom system and a 9-story steel building, each using a 200-kN large-scale magnetorheological damper as the rate-dependent physical specimen.
Keywords: RTHS, Experimental
Authors: Brian M. Phillips, A.M.ASCE; and Billie F. Spencer Jr., P.E., F.ASCE
DOI: 10.1061/(ASCE)EM.1943-7889.0000493
Abstract: Hybrid simulation combines numerical simulation and experimental testing in a loop of action and reaction to capture the dynamic behavior of a structure. With an extended time scale, convergence of the desired displacements or forces can be assured in each actuator connected to the experimental component before advancing to the next time step. However, when the rate-dependent behavior of an experimental component is of interest, the hybrid simulation must be conducted in real time [i.e., real-time hybrid simulation (RTHS)]. In RTHS, the dynamic behavior of the loading system (i.e., actuators, controllers, and computers) is directly introduced into the RTHS loop. These dynamics consist of both time delays and frequency dependent time lags. At the same time, the phenomenon of control-structure interaction leads to a coupling of the dynamic behavior of the actuators and the structure. Traditional actuator control approaches for RTHS compensate for an apparent time delay or time lag rather than address the actuator dynamics directly. Moreover, most actuator control approaches focus on single-actuator systems. The RTHS control approach proposed herein directly addresses actuator dynamics through model-based feedforward-feedback control. Capturing the dynamic coupling between the actuators ensures accurate control for multiactuator systems. The proposed approach is illustrated through numerical simulation for a 3-story building with multiple actuators to provide control during RTHS.
Keywords: RTHS, Experimental
Authors: Cheng Chen; James M. Ricles; Theodore L. Karavasilis; Yunbyeong Chae; and Richard Sause
DOI: 10.1016/j.engstruct.2011.10.006
Abstract: Real-time hybrid simulation is a viable experiment technique to evaluate the performance of structural systems subjected to earthquake loads. This paper presents details of the real-time hybrid simulation system developed at Lehigh University, including the hydraulic actuators, the IT control architecture, an integration algorithm and actuator delay compensation. An explicit integration algorithm provides a robust and accurate solution to the equations of motion while an adaptive inverse compensation method ensures the accurate application of the command displacements to experimental substructure(s) by servo-hydraulic actuators. Experiments of a steel moment resisting frame with magneto-rheological fluid dampers in passive-on mode were conducted using the real-time hybrid simulation system to evaluate the ability for the simulation method to evaluate the nonlinear seismic response of steel frame systems with dampers that are intended to enhance the response of the structure. The comparison with numerical simulation results demonstrates that the real-time hybrid simulation system produces accurate and reliable experimental results and therefore shows great potential for structural performance evaluation in earthquake engineering research.
Keywords: Earthquake, RTHS, Nonlinear, Algorithms, Experimental
Authors: Takehiko Asai; Chia-Ming Chang; Brian M. Phillips; and B.F. Spencer Jr.
DOI: 10.1016/j.engstruct.2013.09.016
Abstract: Smart outrigger damping systems have been proposed as a novel energy dissipation system to protect high-rise buildings from severe earthquakes and strong winds. In these damping systems, devices such as magnetorheological (MR) dampers are installed vertically between the outrigger and perimeter columns to achieve large and adaptable energy dissipation. To complement the high performance shown in previous theoretical studies, this control approach needs to be experimentally verified. To examine a smart outrigger damping system experimentally, real-time hybrid simulation (RTHS) provides an alternative where the damping devices can be experimentally tested, while the remaining components in the structural system are simultaneously tested through numerical simulation. The focus of this study is to experimentally investigate and verify smart outrigger damping systems for high-rise buildings subject to scaled El Centro and Kobe earthquake records using RTHS. Through RTHS, the efficacy of the smart outrigger damping system is demonstrated for two historical earthquakes.
Keywords: Earthquake, Wind, RTHS, Experimental
Authors: S H Eem; H J Jung; and J H Koo
DOI: 10.1088/0964-1726/22/5/055003
Abstract: Recently, magneto-rheological (MR) elastomer-based base isolation systems have been actively studied as alternative smart base isolation systems because MR elastomers are capable of adjusting their modulus or stiffness depending on the magnitude of the applied magnetic field. By taking advantage of the MR elastomers' stiffness-tuning ability, MR elastomer-based smart base isolation systems strive to alleviate limitations of existing smart base isolation systems as well as passive-type base isolators. Until now, research on MR elastomer-based base isolation systems primarily focused on characterization, design, and numerical evaluations of MR elastomer-based isolators, as well as experimental tests with simple structure models. However, their applicability to large civil structures has not been properly studied yet because it is quite challenging to numerically emulate the complex behavior of MR elastomer-based isolators and to conduct experiments with large-size structures. To address these difficulties, this study employs the real-time hybrid simulation technique, which combines physical testing and computational modeling. The primary goal of the current hybrid simulation study is to evaluate seismic performances of an MR elastomer-based smart base isolation system, particularly its adaptability to distinctly different seismic excitations. In the hybrid simulation, a single-story building structure (non-physical, computational model) is coupled with a physical testing setup for a smart base isolation system with associated components (such as laminated MR elastomers and electromagnets) installed on a shaking table. A series of hybrid simulations is carried out under two seismic excitations having different dominant frequencies. The results show that the proposed smart base isolation system outperforms the passive base isolation system in reducing the responses of the structure for the excitations considered in this study.
Keywords: Earthquake, RTHS, Large Scale, Experimental
Authors: Victor Saouma, Ph.D.; Gary Haussmann, Ph.D.; Dae-Hung Kang, Ph.D.; and Wassim Ghannoum, Ph.D., A.M.ASCE
DOI: 10.1061/(ASCE)ST.1943-541X.0000813
Abstract: This paper reports about a real-time hybrid simulation (RTHS) of a nonductile reinforced concrete frame that had previously been tested on a shake table (ST) at the University of California, Berkeley. This three-story, three-bay frame is numerically modeled with flexibility-based/layered nonlinear elements and over 400 degrees of freedom (DOFs), while one of the nonductile base columns is physically tested in the laboratory. RTHS is enabled through a new code developed by the authors, and these simulation results are compared with those obtained from the ST test. The comparison between ST tests and RTHS is encouraging, though still not acceptable (within 10%). Details of the simulation are provided, and preliminary results indicate that RTHS may be indeed provide the natural path for a gradual substitution of physical (and expensive) testing by numerical simulation. This contribution offers a small step in that direction.
Keywords: RTHS, Nonlinear
Authors: Ali Ashasi-Sorkhabi; Hadi Malekghasemi; and Oya Mercan
DOI: 10.1177/1077546313498616
Abstract: In this study, as a state of the art testing method, real-time hybrid simulation (RTHS) is implemented and verified with a shake table for education and research. As an application example, the dynamic behavior of a tuned liquid damper (TLD)-structure system is investigated. RTHS is a practical and economical experimental technique which complements the strengths of computer simulation with physical testing. It separates the test structure into two substructures where part of the structure for which a reliable analytical model is not available is tested physically (experimental substructure) and coupled together with the analytical model of the remaining structure (analytical substructure). The implementation of RTHS involves challenges in accurate control of the experimental substructure as well as the synchronization of the signals. The details of the hardware and the software developed and the steps taken to improve the controller are discussed in this paper so that the implementation of RTHS is properly introduced. The accuracy has been verified using tracking indicators as well as using the response obtained from a spring-mass oscillator and TLD system. The shake table used in this study is available in over 100 universities around the world. In this paper, the implementation of RTHS is provided with sufficient details to enable easy introduction of this testing method wherever a similar shake table is available. This additional functionality will not only provide a new research tool, but it will also facilitate classroom demonstrations to improve how students understand new concepts in structural dynamics and earthquake engineering.
Keywords: Earthquake, RTHS, Experimental, Education, Controller Design
Authors: Tong Guo; Cheng Chen; WeiJie Xu; and Frank Sanchez
DOI: 10.1088/0964-1726/23/4/045042
Abstract: Real-time hybrid simulation is a viable and economical technique that allows researchers to observe the behavior of critical elements at full scale when an entire structure is subjected to dynamic loading. To ensure reliable experimental results, it is necessary to evaluate the actuator tracking after the test, even when sophisticated compensation methods are used to negate the detrimental effect of servo-hydraulic dynamics. Existing methods for assessment of actuator tracking are often based on time-domain analysis. This paper proposes a frequency-domain-based approach to the assessment of actuator tracking for real-time hybrid simulations. To ensure the accuracy of the proposed frequency response approach, the effects of spectrum leakage are investigated as well as the length and sampling frequency requirements of the signals. Two signal pre-processing techniques (data segmentation and window transform) are also discussed and compared to improve the accuracy of the proposed approach. Finally the effectiveness of the proposed frequency-domain-based approach is demonstrated through both computational analyses and laboratory tests, including real-time tests with predefined displacement and real-time hybrid simulation.
Keywords: RTHS, Experimental
Authors: Elif Ecem Bas; Mohamed A. Moustafa; and Gokhan Pekcan
DOI: 10.1080/13632469.2020.1733138
Abstract: Hybrid Simulation (HS) is a well-established testing method that combines both experimental and analytical components to evaluate the performance of structures under extreme events, commonly earthquakes. While several configurations and systems are available around the world to conduct HS, one goal of this paper is to document the development and verification of a compact HS setup at the University of Nevada, Reno to be used for tackling new research problems and educational purposes. A new substructured HS approach is proposed for seismic testing of concentric-braced frames (CBFs) with focus on capturing brace buckling and low-cycle fatigue induced-rupture. The paper presents the capabilities and verification methods for the developed system for slow and real-time HS testing with two different alternatives for the computational substructures: Simulink and OpenSEES along with OpenFresco. Two new applications were pursued to demonstrate HS testing of CBFs. The first used cyclic loading and HS under earthquake loading to capture brace buckling and failure to compare damage accumulation and brace fatigue life through rupture. The second application used HS testing to investigate the effect of earthquake duration on seismic performance of CBFs. The two applications demonstrate that the proposed HS approach can be potentially used to accurately capture CBFs seismic behavior and provide new datasets for modeling brace buckling and rupture under realistic earthquake loading. The paper also provides a brief discussion on the potential use of the compact HS setup for developing teaching modules.
Keywords: Earthquake, RTHS, Nonlinear, Experimental, Education, Case Study
Authors: E. E. Bas; and M. A. Moustafa
DOI: 10.1007/s40799-020-00385-6
Abstract: Hybrid simulation (HS) and real-time HS (RTHS) are widely used experimental techniques to evaluate the seismic performance of structural components and full systems. The goal of this study is to investigate the performance and limitations of RTHS when the computational model involves complex and highly nonlinear behavior, mainly due to both stiffness and strength deterioration. To establish the case of deploying such heavily nonlinear models, a RTHS methodology is presented to study the effect of using braces for seismic retrofitting of older steel moment resisting frames (MRFs). The objective of this paper is two-fold. First, assess the performance and identify limitations of integration algorithms for RTHS with heavily nonlinear models. Second, demonstrate the feasibility of HS/RTHS testing for selecting the best seismic retrofitting strategies. A comprehensive analytical study of different MRFs models is presented to study the performance of different integration algorithms available in OpenSees. Selected MRF model is modified to conduct a series of nonlinear RTHS tests using a compact HS test setup at the University of Nevada, Rene. The performance of two implicit and explicit integration algorithms is assessed for RTHS, and the quality of HS results from RTHS and slow HS tests are compared. Moreover, a demonstration of how HS could be used for assessing best seismic retrofitting strategies based on realistic nonlinear models is presented.
Keywords: Earthquake, RTHS, Nonlinear, Experimental, Case Study
Authors: T. Sauder
DOI: 10.1007/s40799-020-00372-x
Abstract: Cyber-physical empirical methods enable to address problems that classical empirical methods alone, or models alone, cannot address in a satisfactory way. In CPEMs, the substructures are interconnected through a control system that includes sensors and actuators, having their own dynamics. The present paper addresses how the fidelity of CPEMs, that is the degree to which they reproduce the behaviour of the real system under study, is affected by the presence of this control system. We describe an analysis method that enables the designer of a CPEM to (1) identify the artefacts (such as biases, noise, or delays) that play a significant role for the fidelity, (2) define bounds for the describing parameter of these artefacts ensuring high-fidelity of the CPEM, and (3) evaluate whether probabilistic robust fidelity is achieved. The proposed method is illustrated by considering a substructured slender structure subjected to dynamic loading.
Keywords: Earthquake, Fire, Wind, Wave, RTHS, UQ, Machine Learning, Theory, Algorithms, Case Study, Transfer Systems, Controller Design
Authors: Maxime Thys; Valentin Chabaud; Thomas Sauder; Lene Eliassen; Lars O. Sæther; and Øyvind B. Magnussen
DOI: 10.1115/IOWTC2018-1081
Abstract: This article presents the Real-Time Hybrid Model (ReaTHM®) tests that were performed on a 10-MW semi-submersible floating wind turbine in the Ocean Basin at SINTEF Ocean in March 2018. The ReaTHM test method was used for the model tests to circumvent the limitations encountered when performing model tests with wind and waves. The physical model was subject to physical waves, while the rotor and tower loads were simulated in real-time and applied on the model by use of a cable-driven parallel robot. Recent advances in the ReaTHM test method allowed for extended testing possibilities and load application up to the 3p frequency and the first tower bending frequency.
Keywords: Wind, Wave, RTHS, Experimental
Authors: Valentin Chabaud; Lene Eliassen; Maxime Thys; and Thomas Sauder
DOI: 10.1088/1742-6596/1104/1/012021
Abstract: Model testing of offshore structures in ocean basins has been accepted as a necessary step for the validation and calibration of numerical models, as well as for final design checks in extreme environments. While offshore wind power makes no exception, model testing has not shown its full potential due to inherent modeling challenges. Generating highly-controlled wind fields in ocean basins and alleviating aerodynamic modeling errors due to Reynolds number mismatch in Froude-based scaling are prominent examples. To circumvent these issues, the concept of Real-Time Hybrid Model (ReaTHM) testing has been suggested by SINTEF Ocean and NTNU, Norway. Here the wind loads are no longer physically modeled but computed from online-measured motions and a numerical wind field. They are then actuated in real time on the scale model by means of actuators, while subjected to -physical-wave and current loads. This paper aims at presenting design considerations regarding the choice of the actuator(s) and its/their interface with the scale model. The pros and cons of the chosen solution, namely cable-driven parallel robots using industrial servo drives, are presented. The focus is then directed toward the mapping between wind loads to be actuated and tension commands on each cable, called tension allocation. Two layouts corresponding to two ReaTHM testing campaigns performed in SINTEF Ocean's ocean basin are then compared on various aspects, with emphasis on tension allocation. In addition to proving the feasibility of the chosen technical solution, results show a tradeoff between flexibility (with respect among others to wind direction) and usability on other structures versus minimization of cable tensions. The latter aspect is treated in detail, using theory first adapted from literature on cable-driven parallel robots, then illustrated through relevant examples for the current application.
Keywords: Wind, Wave, RTHS, Algorithms, Experimental, Case Study, Transfer Systems, Controller Design
Authors: Sauder Thomas Michel; Chabaud Valentin Bruno; Thys Maxime; Bachynski Erin Elizabeth; and Sæther Lars Ove
DOI: 10.1115/OMAE2016-54435
Abstract: This article presents a method for performing Real-Time Hybrid Model testing (ReaTHM testing) of a floating wind turbine (FWT). The advantage of this method compared to the physical modelling of the wind in an ocean basin, is that it solves the Froude-Reynolds scaling conflict, which is a key issue in FWT testing. ReaTHM testing allows for more accurate testing also in transient conditions, or degraded conditions, which are not feasible yet with physical wind. The originality of the presented method lies in the fact that all aerodynamic load components of importance for the structure were identified and applied on the physical model, while in previous similar projects, only the aerodynamic thrust force was applied on the physical model. The way of applying the loads is also new. The article starts with a short review (mostly references) of ReaTHM testing when applied to other fields than marine technology. It then describes the design of the hybrid setup, its qualification, and discusses possible error sources and their quantification. The second part of the article [1] focuses on the performance of a braceless semi-submersible FWT, tested with the developed method. The third part [2] describes how the experimental data was used to calibrate a numerical model of the FWT.
Keywords: Wind, Wave, RTHS, Experimental, Case Study
Authors: Fei Zhu; Jin-Ting Wang; Feng Jin; and Li-Qiao Lu
DOI: 10.1016/j.engstruct.2017.02.004
Abstract: This paper aims to demonstrate the real performance of tuned liquid column dampers (TLCDs) in controlling seismic response of multi-degree-of-freedom (MDOF) structures based on the advantages of real-time hybrid simulation (RTHS). An RTHS framework is developed to carry out full-scale experiments of TLCD-structure-foundation system, and the application of multiple TLCDs to control single-order and multi-order modal responses of a nine-story benchmark building is investigated, respectively, as an example. Moreover, the effect of soil–structure interaction (SSI) on TLCD performance is examined, in which the finite and semi-infinite soil flexible foundations are simulated through a finite element model with 1160 DOFs embedding fixed and artificial boundaries, respectively. Results show that MTLCD is more effective than a single TLCD in suppressing structural responses; and the former is suggested to be used to control multi-order modal responses because of the uncertainty of the frequency content of earthquake excitations. The SSI effect significantly reduces TLCD performance, and the semi-infinite foundation may eliminate the control effect of TLCD due to the radiation damping effect. The parameters of the TLCD device should be regulated according to the characteristics of SSI-structure system when the SSI effect is unneglectable.
Keywords: Earthquake, RTHS, UQ, Experimental, Benchmark
Authors: Cheng Chen; and James M. Ricles
DOI: 10.1002/eqe.1172
Abstract: Real‐time hybrid simulation is a viable experiment technique to evaluate the performance of structures equipped with rate‐dependent seismic devices when subject to dynamic loading. The integration algorithm used to solve the equations of motion has to be stable and accurate to achieve a successful real‐time hybrid simulation. The implicit HHT α‐algorithm is a popular integration algorithm for conducting structural dynamic time history analysis because of its desirable properties of unconditional stability for linear elastic structures and controllable numerical damping for high frequencies. The implicit form of the algorithm, however, requires iterations for nonlinear structures, which is undesirable for real‐time hybrid simulation. Consequently, the HHT α‐algorithm has been implemented for real‐time hybrid simulation using a fixed number of substep iterations. The resulting HHT α‐algorithm with a fixed number of substep iterations is believed to be unconditionally stable for linear elastic structures, but research on its stability and accuracy for nonlinear structures is quite limited. In this paper, a discrete transfer function approach is utilized to analyze the HHT α‐algorithm with a fixed number of substep iterations. The algorithm is shown to be unconditionally stable for linear elastic structures, but only conditionally stable for nonlinear softening or hardening structures. The equivalent damping of the algorithm is shown to be almost the same as that of the original HHT α‐algorithm, while the period elongation varies depending on the structural nonlinearity and the size of the integration time‐step. A modified form of the algorithm is proposed to improve its stability for use in nonlinear structures. The stability of the modified algorithm is demonstrated to be enhanced and have an accuracy that is comparable to that of the existing HHT α‐algorithm with a fixed number of substep iterations. Both numerical and real‐time hybrid simulations are conducted to verify the modified algorithm. The experimental results demonstrate the effectiveness of the modified algorithm for real‐time testing.
Keywords: Earthquake, RTHS, Nonlinear, Algorithms, Experimental
Authors: Yunbyeong Chae; James M. Ricles; and Richard Sause, M.ASCE
DOI: 10.1061/(ASCE)ST.1943-541X.0000691
Abstract: Real-time hybrid simulations using large-scale magnetorheological (MR) dampers were conducted to evaluate the performance of various structural control strategies to control the seismic response of a three-story steel-frame building. Magnetorheological dampers were installed in the building to limit the story drift to less than 1.5% under the design-basis earthquake (DBE). The laboratory specimens, referred to as experimental substructures, were two individual MR dampers, with the remainder of the building modeled as a nonlinear analytical substructure. The experimental technique enables an ensemble of ground motions to be applied to the building, resulting in various levels of damage, without the need to repair the experimental substructures because the damage will be within the analytical substructure. Five different damper control algorithms, including passive and semiactive control algorithms, were selected. An ensemble of five ground motions scaled to the DBE was used for the real-time hybrid simulations to obtain statistical responses of the structure for each control. The real-time hybrid simulation results show that the MR dampers can control the drift, enabling the performance objective of 1.5% maximum story drift to be achieved. Although some semiactive controllers show better performance for a specific ground motion, the response statistics from the real-time hybrid simulations show that the overall performance of the semiactive control algorithms with the selected user-defined parameters is similar to that for the passive controller for the three-story building used in this study. A comparison of real-time hybrid simulation results with numerical simulation results using OpenSees was conducted to further gain insight into the performance of the damper control algorithms observed in the real-time hybrid simulations.
Keywords: Earthquake, RTHS, Nonlinear, Large Scale, Algorithms, Experimental, Controller Design
Authors: Salvatore Strano; and Mario Terzo
DOI: 10.1007/s11071-016-2831-0
Abstract: In real-time hybrid simulation, hydraulic actuators, equipped with suitable controllers, are typically used to impose displacements to experimental substructures. Interaction between actuators and physical substructures can result in a nonlinear behaviour of the overall experimental testing system (ETS), making the controller design very challenging. The accuracy of the hydraulic actuation system (HAS) is very crucial because actuator displacement errors lead to incorrect simulation results. For this purpose, several methods have been developed by researchers in order to compensate tracking error of HASs. This paper presents a novel adaptive compensator that takes into account the actual ETS dynamics by adopting an extend Kalman filter for the real-time estimation of the ETS model parameters. The adaptive approach improves the actuator control accuracy and avoids ad hoc system identification procedures. The novel compensator has been verified experimentally on a test rig for seismic isolator shear tests. The feasibility of the proposed compensation method has been also demonstrated through real-time hybrid simulation of a building with a base isolation system. Both numerical and experimental results confirmed that the proposed compensation strategy provides good results even in the case of inevitable nonlinearities of the ETS. Furthermore, the method has also demonstrated good performance in terms of stability and robustness with respect to variations of the operating conditions.
Keywords: Earthquake, RTHS, Nonlinear, Experimental, Controller Design
Authors: Azin Ghaffary; and Reza Karami Mohammadi
DOI: 10.1002/tal.1606
Abstract: Magnetorheological (MR) dampers have gained significant attention in seismic mitigation of structural systems due to their distinguished characteristics such as inherent stability and minimum power requirements. Their performance in control of nonlinear structural response, however, has not been widely investigated. This paper provides comprehensive nonlinear seismic performance assessment of a three‐story benchmark structure equipped with a large‐scale MR damper using virtual real‐time hybrid simulation to efficiently capture the nonlinear behavior of the damper. The framework is first verified by means of available experimental results of an actual RTHS on the same structural system. A set of 12 earthquake ground motions, each one scaled to have 12 different intensities are then utilized to perform nonlinear dynamic analyses. An energy‐based adaptive passive‐on control strategy is proposed, and its performance is compared with passive‐on, passive‐off, and uncontrolled response of the structure in terms of interstory drifts shown by fragility curves, residual drifts, MR damper control force, and the ability to maintain a uniform interstory drift along the height of the structure.
Keywords: Earthquake, RTHS, Nonlinear, Large Scale, Experimental, Benchmark
Authors: Seung-Hyun Eem; Jeong-Hoi Koo; and Hyung-Jo Jung
DOI: 10.1177/1045389X18754347
Abstract: This article investigates an adaptive mount system based on magnetorheological elastomer in reducing the vibration of an equipment on the isolation table. Incorporating MR elastomers, whose elastic modulus or stiffness can be adjusted depending on the applied magnetic field, the proposed mount system strives to alleviate the limitations of existing passive-type mount systems. The primary goal of this study is to evaluate the vibration reduction performance of the proposed MR elastomer mount using the hybrid simulation technique. For real-time hybrid simulations, the MR elastomer mount and the control system are used as an experimental part, which is installed on the shaking table, and an equipment on the table is used as a numerical part. A suitable control algorithm is designed for the real-time hybrid simulations to avoid the responses of the equipment’s natural frequency by tracking the frequencies of the responses. After performing a series of real-time hybrid simulation on the adaptive mount system and the passive-type mount system under sinusoidal excitations, this study compares the effectiveness of the adaptive mount system over its passive counterpart. The results show that the proposed adaptive elastomer mount system outperforms the passive-type mount system in reducing the responses of the equipment for the excitations considered in this study.
Keywords: RTHS, Algorithms, Experimental
Authors: Ruiyang Zhang; Paige V. Lauenstein; and Brian M. Phillips
DOI: 10.1016/j.engstruct.2016.04.022
Abstract: Recent investments in earthquake engineering research have produced an array of experimental equipment and testing capabilities worldwide. Laboratories are often equipped with shake tables, ranging from uni-axial tables to six-degree-of-freedom tables to multiple table arrays. These tables are capable of providing interface boundary conditions for substructure real-time hybrid simulation (RTHS). In the simplest case, the lower stories of a shear building are simulated numerically while the upper stories tested experimentally. Even this simple case reveals the challenges of RTHS using shake tables. Shake tables are highly nonlinear devices, making modeling and control a challenging task. Furthermore, the mass of the test specimen is typically large relative to the capacity of the table, leading to substantial coupling of the table and specimen dynamics. These challenges are exacerbated by the loop of action and reaction between numerical and experimental components in RTHS. Any delay or lag in the realization of the desired table trajectory and measurement of the base shear can introduce inaccuracies and instabilities into the loop. This research investigates the challenges of RTHS using shake tables through a simple uni-axial shake table and shear building specimen. A model-based shake table control approach is successfully implemented for online acceleration tracking. A Kalman filter is used to reduce measurement noise in the RTHS loop without introducing phase lag. Numerical and experimental substructures with low damping are selected to demonstrate the robustness of the proposed framework for a challenging RTHS scenario. Even for shake tables with large control-structure interaction and structures with low damping, the proposed framework is robust, reliable, and uses readily available equipment, providing a new experimental tool for laboratories with modest experimental testing capabilities.
Keywords: Earthquake, RTHS, Nonlinear, Experimental
Authors: Phillips, Brian M.; Takada, Shuta; Spencer, B.F. Jr.; and Fujino, Yozo
DOI: 10.12989/sss.2014.14.6.1081
Abstract: Real-time hybrid simulation (RTHS) has emerged as an important tool for testing large and complex structures with a focus on rate-dependent specimen behavior. Due to the real-time constraints, accurate dynamic control of servo-hydraulic actuators is required. These actuators are necessary to realize the desired displacements of the specimen, however they introduce unwanted dynamics into the RTHS loop. Model-based actuator control strategies are based on linearized models of the servo-hydraulic system, where the controller is taken as the model inverse to effectively cancel out the servo-hydraulic dynamics (i.e., model-based feedforward control). An accurate model of a servo-hydraulic system generally contains more poles than zeros, leading to an improper inverse (i.e., more zeros than poles). Rather than introduce additional poles to create a proper inverse controller, the higher order derivatives necessary for implementing the improper inverse can be calculated from available information. The backward-difference method is proposed as an alternative to discretize an improper continuous time model for use as a feedforward controller in RTHS. This method is flexible in that derivatives of any order can be explicitly calculated such that controllers can be developed for models of any order. Using model-based feedforward control with the backward-difference method, accurate actuator control and stable RTHS are demonstrated using a nine-story steel building model implemented with an MR damper.
Keywords: RTHS, Controller Design
Authors: Jinting Wang; Liqiao Lu; and Fei Zhu
DOI: 10.1007/s11803-018-0426-0
Abstract: Finite element (FE) is a powerful tool and has been applied by investigators to real-time hybrid simulations (RTHSs). This study focuses on the computational efficiency, including the computational time and accuracy, of numerical integrations in solving FE numerical substructure in RTHSs. First, sparse matrix storage schemes are adopted to decrease the computational time of FE numerical substructure. In this way, the task execution time (TET) decreases such that the scale of the numerical substructure model increases. Subsequently, several commonly used explicit numerical integration algorithms, including the central difference method (CDM), the Newmark explicit method, the Chang method and the Gui-λ method, are comprehensively compared to evaluate their computational time in solving FE numerical substructure. CDM is better than the other explicit integration algorithms when the damping matrix is diagonal, while the Gui-λ (λ = 4) method is advantageous when the damping matrix is non-diagonal. Finally, the effect of time delay on the computational accuracy of RTHSs is investigated by simulating structure-foundation systems. Simulation results show that the influences of time delay on the displacement response become obvious with the mass ratio increasing, and delay compensation methods may reduce the relative error of the displacement peak value to less than 5% even under the large time-step and large time delay.
Keywords: RTHS, Algorithms
Authors: Miguel Saez; Francisco Maturana; Kira Barton; and Dawn Tilbury
DOI: 10.1109/CoASE.2015.7294133
Abstract: Simulation is a common way to analyze the performance of a manufacturing system. On a system level, entities are modeled based on production and failure rates using Discrete Event Simulation (DES). On a machine level, the Continuous Dynamics (CD) of machines are studied based on position, velocity, and acceleration. However, these models are usually run separately, losing key information that could be used for more accurate control of the system performance. In this paper, we merge DES and CD in a single hybrid simulation environment. By synchronizing the simulations to run in realtime, the results can be compared with information from the plant floor. Using the simulation outcome as a reference, any significant deviation of the plant floor performance would represent an error and would trigger an event that can be automated or inform an operator of a required action.
Keywords: RTHS
Authors: Ashasi-Sorkhabi, Ali; and Mercan, Oya
DOI: 10.12989/sss.2014.14.6.1151
Abstract: This paper presents a user programmable computational/control platform developed to conduct real-time hybrid simulation (RTHS). The architecture of this platform is based on the integration of a real-time controller and a field programmable gate array (FPGA).This not only enables the user to apply user-defined control laws to control the experimental substructures, but also provides ample computational resources to run the integration algorithm and analytical substructure state determination in real-time. In this platform the need for SCRAMNet as the communication device between real-time and servo-control workstations has been eliminated which was a critical component in several former RTHS platforms. The accuracy of the servo-hydraulic actuator displacement control, where the control tasks get executed on the FPGA was verified using single-degree-of-freedom (SDOF) and 2 degrees-of-freedom (2DOF) experimental substructures. Finally, the functionality of the proposed system as a robust and reliable RTHS platform for performance evaluation of structural systems was validated by conducting real-time hybrid simulation of a three story nonlinear structure with SDOF and 2DOF experimental substructures. Also, tracking indicators were employed to assess the accuracy of the results.
Keywords: RTHS, Nonlinear, Algorithms, Experimental, Controller Design
Authors: Cheng Chen; Jose Valdovinos; and Hector Santiallno
DOI: 10.1061/9780784412848.205
Abstract: Real-time hybrid simulation replicates structural responses under earthquakes through integrating physical testing of experimental substructures and numerical modeling of analytical substructures. Experimental studies, however, indicated that actuator delay-induced tracking errors are often inevitable even when a sophisticated actuator delay compensation technique is applied. Reliability assessment of real-time hybrid simulation results is, therefore, necessary to correctly interpret for structure performance evaluation. This, however, could be difficult since exact structural response is often not available for an immediate comparison. This paper proposes a reliability assessment approach for real-time hybrid simulation results. Statistical distribution of actuator delay values corresponding to certain accuracy level established for linear elastic single-degree-of-freedom structures is modified to account for structural nonlinearity. An existing tracking indicator is then utilized to incorporate the probabilistic distribution of this actuator delay to assess the reliability of real-time hybrid simulation results. Real-time hybrid simulations of a steel moment resisting frame with an elastomeric damper are used to demonstrate the application of proposed approach.
Keywords: Earthquake, RTHS, Nonlinear, Experimental
Authors: Fei Zhu; Jin-Ting Wang; Feng Jin; and Li-Qiao Lu
DOI: 10.1080/13632469.2016.1138170
Abstract: This article presents real-time hybrid simulation (RTHS) in a single-degree-of-freedom (SDOF) steel frame incorporated with tuned liquid column damper (TLCD). The SDOF steel frame is numerically simulated, and the TLCD alone is physically experimented on a shaking table. The delay-dependent stability of RTHS system for TLCD investigation is first assessed; and the delay-dependent accuracy is verified by comparing the responses obtained through the RTHS, the conventional shaking table test, and an analytical solution. Then, RTHSs are carried out to evaluate the effects of mass ratio, structural damping ratio, structural stiffness, and peak ground acceleration on the reduction effectiveness of STLCD. The nonlinear behavior of the STLCD is experimentally captured. Finally, the structural responses under STLCD and multiple TLCDs (MTLCD) control are compared. It is found that the performance of STLCD strongly depends on structural parameters and properties of earthquakes; both MTLCD and STLCD induce approximately the same response reductions, and the former can enhance the control performance in certain cases. These results presented here may contribute to improve the design and application of TLCDs in practical engineering.
Keywords: Earthquake, RTHS, Nonlinear, Experimental
Authors: Yunbyeong Chae ; Stephanie Tong ; Thomas M. Marullo ; and James M. Ricles
DOI: 10.1061/9780784412374.032
Abstract: Real-time hybrid simulation combines physical testing (experimental substructuring) and numerical simulation (analytical substructuring) such that the dynamic performance of the entire structural system can be considered during the simulation. A grid-based real-time hybrid simulation technique is introduced as a means to perform real-time hybrid simulations of complex structural systems where the analytical substructure poses a large computational demand. Real-time hybrid simulations of the 9-story ASCE benchmark structure with large-scale magnetorheological (MR) dampers are performed at the Lehigh NEES Equipment Site to demonstrate the multi-grid real-time hybrid simulation procedure and illustrate the ability to significantly reduce the time to perform the state determination of the analytical substructure. The 9-story building structure is modeled as the analytical substructure, with the experimental substructure consisting of large-scale MR dampers that are located in the structure. The analytical substructure is divided into two parts and implemented onto a computational grid consisting of two parallel xPCs that run MathWorks real-time Target PC software package. The restoring force data from these two xPCs are synchronized together along with the measured damper forces from the experimental substructure, and processed in a real-time manner for each time step of the hybrid simulation. The results of real-time hybrid simulation are compared to those of numerical simulations to validate the new test methodology.
Keywords: Earthquake, RTHS, Large Scale, Experimental, Benchmark
Authors: Feleb N. Matti; and Fidelis R. Mashiri
DOI: 10.1504/IJLCPE.2020.108950
Abstract: Welded tubular square hollow section (SHS) joints are widely used in numerous structures such as steel bridges and tower structures. These structures are susceptible to fatigue failure caused by cyclic axial loadings, in-plane and out-of-plane loadings. Concrete filling the hollow section of the joints' chord is necessary to improve the strength of structures and their fatigue life and decreases stresses at the hot spot locations of the joints. Concrete-filled SHS/RHS members are also briefly included in the review to show the benefits of concrete-filled tubes under fire impact and bearing. There is no existing fatigue design guide for welded composite tubular joints due to limited results relating to the concrete grades, size range of hollow structural steel sections and joint types. The purpose of this paper is to summarise and present researches that have been conducted on empty and composite SHS joints under static and fatigue loadings and highlight the research gap. Previous experimental studies and/or numerical studies on tubular SHS joints with concrete-filled chords and empty joints with SHS are studied and summarised. Recommendations for future work are given.
Keywords: Hybrid Simulation, Experimental
Authors: Ramla Karim Qureshi; Negar Elhami-Khorasani; and Thomas Gernay
DOI: 10.1108/JSFE-12-2018-0042
Abstract: This paper aims to investigate the need for active boundary conditions during fire testing of structural elements, review existing studies on hybrid fire testing (HFT), a technique that would ensure updating of boundary conditions during a fire test, and propose a compensation scheme to mitigate instabilities in the hybrid testing procedure. The paper focuses on structural steel columns and starts with a detailed literature review of steel column fire tests in the past few decades with varying axial and rotational end restraints. The review is followed with new results from comparative numerical analyses of structural steel columns with various end constraints. HFT is then discussed as a potential solution to be adapted for fire testing of structural elements. Challenges in contemporary HFT procedures are discussed, and application of stiffness updating approaches is demonstrated. The reviewed studies indicate that axial and rotational restraints at the boundaries considerably influence the fire response of steel columns. Equivalent static spring technique for simulating effect of surrounding frame on an isolated column behavior does not depict accurate buckling and post-buckling response. Additionally, numerical models that simulate fire performance of a column situated in a full-frame do follow the trends observed in actual test results up until failure occurs, but these simulations do not necessarily capture post-failure performance accurately. HFT can be used to capture proper boundary conditions during testing of isolated elements, as well as correct failure modes. However, existing studies showed cases with instabilities during HFT. This paper demonstrates that a different stiffness updates calculated from the force-displacement response history of test specimen at elevated temperature can be used to resolve stability issues. The paper has two contributions: it suggests that the provision of active boundary conditions is needed in structural fire testing, as equivalent static spring does not necessarily capture the effect of surrounding frame on an isolated element during a fire test, and it shows that force-displacement response history of test specimen during HFT can be used in the form of a stiffness update to ensure test stability.
Keywords: Fire, RTHS, Nonlinear, Theory, Education, Benchmark
Authors: Zhu Fei; Wang Jinting; Jin Feng; and Lu Liqiao
DOI: 10.1007/s11803-019-0530-9
Abstract: Tuned liquid damper (TLD) and tuned liquid column damper (TLCD) are two types of passive control devices that are widely used in structural control. In this study, a real-time hybrid simulation (RTHS) technique is employed to investigate the difference in control performance between TLD and TLCD. A series of RTHSs is presented with the premise of the same liquid length, mass ratio, and structural parameters. Herein, TLD and TLCD are physically experimented, and controlled structures are numerically simulated. Then, parametric studies are performed to further evaluate the different performance between TLD and TLCD. Experimental results demonstrate that TLD is more effective than TLCD under different amplitude excitations.
Keywords: Earthquake, RTHS, Experimental
Authors: Ge Ou; Ge Yang; Shirley Dyke; and Bin Wu
DOI: 10.3389/fbuil.2020.00103
Abstract: In hybrid simulation, response time history measured from an experimental substructure can be utilized to identify the model associated with the tested specimen in real time. To improve the modeling accuracy, the updated model parameters can substitute the initial parameters of similar components (as the tested specimen) that reside in the numerical substructure. In this study, a detailed investigation into the fidelity improvement using model updating in hybrid simulation has been carried out. This study has focused on both local and global assessment of hybrid simulation with model updating (HSMU) by comparing HSMU with conventional simulation and shake table testing. In the local assessment, the updating efficiency with different nonlinemodels (one phenomenological model and one FEM model) have been illustrated; in the global assessment, the HSMU response time histories have been compared to experimental shake table testing. Observations and comments on model selection, parameter convergence, and time and frequency domain performance of HSMU have been provided.
Keywords: Earthquake, Hybrid Simulation, Model Updating, Experimental
Authors: Michael J. Harris; and Richard E. Christenson
DOI: 10.3389/fbuil.2020.00120
Abstract: Base isolation is a well-known technique used to reduce accelerations and inertial forces in structures during earthquakes. However, excessive displacements of the structure due to flexibility of the isolation layer bearings may contribute to moat wall impact events. These impact events have the potential to cause substantial structural damage. This impact behavior and the effects on structural dynamics have been shown to be highly complex and difficult to model by means of pure numerical simulation. In this paper, the cyber-physical technique called Real-Time Hybrid Simulation (RTHS) is employed to capture the uncertainties in force profiles of moat wall impacts and to analyze the complex interactions between impacts and the dynamics of base-isolated structures during earthquake excitations. It is shown that RTHS is capable of accurately capturing the interactions between the isolation layer and moat wall during impact events induced by ground motions. In addition, the RTHS technique is used to analyze the role played by moat wall material nonlinearities in reducing the inertial demand on the structure during impact events. Finally, possible extensions of the research to larger scales as well as consideration of additional moat wall variants are proposed.
Keywords: Earthquake, RTHS, UQ, Nonlinear, Experimental
Authors: Pei-Ching Chen; Meng-Wei Dong; Po-Chang Chen; and Narutoshi Nakata
DOI: 10.3389/fbuil.2020.00109
Abstract: The building mass damper (BMD) system, which incorporates the concept of a tuned mass damper into a mid-story isolation system, has been demonstrated as an effective system for suppressing structural vibration due to earthquakes. The BMD system separates a building into a substructure, a control layer and a superstructure. By applying well-design parameters, the seismic responses of the superstructure and substructure of a building can be mitigated simultaneously. However, merely limited design parameters have been verified by shaking table testing because it is difficult to construct several sets of specimens with limited research funding. Therefore, real-time hybrid simulation (RTHS) may become an alternative to conduct parametric studies of the BMD system efficiently and economically. In this study, the BMD system is separated into a numerical substructure and an experimental substructure. The experimental substructure includes the control layer and the superstructure of the BMD system installed on a seismic shake table while the substructure is numerically simulated. Then, substructuring method of the BMD system is derived and the stability analysis considering the dynamics of the shake table is performed to realize the potential feasibility of RTHS for BMD systems. The stability margin is represented as an allowable mass ratio of the experimental substructure to the entire BMD system. Finally, RTHS of a simplified BMD system has been conducted to verify the stability margin in the laboratory. Phase-lead compensation and force correction are applied to RTHS in order to improve the accuracy of RTHS for the simplified BMD system.
Keywords: Earthquake, RTHS, Experimental
Authors: Yingpeng Tian; Xiaoyun Shao; Huimeng Zhou; and Tao Wang
DOI: 10.3389/fbuil.2020.00123
Abstract: Shaking table substructure testing (STST) takes the substructure with complex behavior physically tested, with the behavior of the rest structural system being numerically simulated. This substructure testing allows the payload of a shaking table being fully utilized in testing of the most concerned part, thus significantly increases its loading capacity. The key to achieve a successful STST is to coordinate among the substructures, specifically, to satisfy compatibility, equilibrium, and synchronization at the boundary between numerical and experimental substructures. A number of studies have focused on the essential techniques of STST, and several applications have been carried out. Nonetheless, its progress is still in the preliminary stage, because of the limited applications using multi-directional shaking tables on large-scale specimens. This paper reviews a series of STSTs and their associated implementation aspects including hybrid testing frameworks, time integration algorithms, delay compensation methods, shaking table and actuator control schemes and boundary force measurement methods. The key techniques required for a successful test are also stressed, such as the force control of actuators to coordination among the substructures. Finally, challenges for future studies and applications are identified and presented.
Keywords: Earthquake, RTHS, Large Scale, Algorithms, Experimental
Authors: Cristóbal Gálmez; and Gastón Fermandois
DOI: 10.3389/fbuil.2020.00134
Abstract: Real-time hybrid simulation (RTHS) is an experimental technique where a critical element of a structural system is tested in the laboratory while the rest is represented through numerical simulations. A challenging aspect of this technique is the correct application of boundary conditions on the experimental substructure using actuators and sensors. The inherent dynamics of an actuator and its interaction with the physical specimen causes a time delay between commanded and measured displacements. It has been shown that delay in RTHS affects the accuracy of an experiment and even can cause instability. Therefore, to avoid stability problems, a proper partitioning choice and an appropriate compensation method for actuator dynamics should be considered. However, there will always be uncertainty in the experimental structure's behavior, so it is essential to check the system's stability during the test execution. In this paper, a stability analysis using energy methods is performed to develop an online stability indicator for the RTHS test. This indicator's goal is to detect stability problems before it can cause excessive displacements in the system, thus avoiding damage in the physical specimen or the laboratory equipment. The effectiveness of the proposed online stability indicator is demonstrated through numerical simulations taking into account the virtual RTHS benchmark problem with different compensation strategies. The proposed indicator is an excellent tool to monitor the RTHS test, improving the reliability of the experimental test while maintaining the safety of the laboratory resources.
Keywords: Earthquake, RTHS, Experimental, Benchmark
Authors: Nikolaos Tsokanas; David Wagg; and Božidar Stojadinović
DOI: 10.3389/fbuil.2020.00127
Abstract: Hybrid simulation is an efficient method to obtain the response of an emulated system subjected to dynamic excitation by combining loading-rate-sensitive numerical and physical substructures. In such simulations, the interfaces between physical and numerical substructures are usually implemented using transfer systems, i.e., an arrangement of actuators. To guarantee high fidelity of the simulation outcome, conducting hybrid simulation in hard real-time is required. Albeit attractive, real-time hybrid simulation comes with numerous challenges, such as the inherent dynamics of the transfer system used, along with communication interrupts between numerical and physical substructures, that introduce time delays to the overall hybrid model altering the dynamic response of the system under consideration. Hence, implementation of adequate control techniques to compensate for such delays is necessary. In this study, a novel control strategy is proposed for time delay compensation of actuator dynamics in hard real-time hybrid simulation applications. The method is based on designing a transfer system controller consisting of a robust model predictive controller along with a polynomial extrapolation algorithm and a Kalman filter. This paper presents a proposed tracking controller first, followed by two virtual real-time hybrid simulation parametric case studies, which serve to validate the performance and robustness of the novel control strategy. Real-time hybrid simulation using the proposed control scheme is demonstrated to be effective for structural performance assessment.
Keywords: Earthquake, RTHS, UQ, Algorithms, Case Study, Transfer Systems, Controller Design
Authors: Moniruzzaman Moni; Youchan Hwang; Oh-Sung Kwon; Ho-Kyung Kim; and Un Yong Jeong
DOI: 10.3389/fbuil.2020.560672
Abstract: The wind tunnel test is one of the most reliable methods for evaluating the dynamic response of high-rise buildings considering wind-structure interaction. In conventional aeroelastic wind tunnel tests, the calibration of stiffnesses, masses and the damping properties of a scaled specimen is required. This takes extensive time and effort, especially when the tests need to be repeated with various geometric designs during design iterations. This study introduces a new testing method that combines a numerical simulation and the conventional aeroelastic wind tunnel test through the real-time hybrid simulation method. The stiffness, damping and partial mass of a scaled building model are represented numerically, while the rest of the mass, the wind-induced pressure around the model and the wind-structure interaction are represented physically in a wind tunnel. The building model in the wind tunnel rests on a base-pivoting system, which is controlled with a linear motor. The base moment induced by wind pressure and the inertial force from the mass of the physical specimen is measured; those measurements are then fed back into a numerical integration scheme. A delay-compensation scheme is implemented to minimize the effects of actuator delay on the dynamic response of the system. Several tests are carried out to validate and calibrate the developed test apparatus and control scheme including (1) tests for the identification of actuator delay, (2) free vibration tests for characterization of the dynamic properties of the hardware and the control system, and (3) wind tunnel tests for system validation through aeroelastic real-time hybrid simulation. This paper presents the overall design of the experimental apparatus, the adopted delay compensation and numerical integration schemes, and a summary of the test results. Test results confirmed that the developed experimental technique can replace the conventional aeroelastic wind tunnel tests of a building model, thus improving the efficiency of the aeroelastic wind tunnel testing.
Keywords: Wind, RTHS, Experimental
Authors: Chengyu Yang; Xuesong Cai; Ziqin Lai; and Yong Yuan
DOI: 10.3389/fbuil.2020.00141
Abstract: In this study, hybrid simulation techniques are used to test earthquake excitation on a supported bridge with High-damping rubber (HDR) bearings, which are widely used in girder bridges. It is impractical to make a full-scale or large-scale test of a whole bridge in the laboratory and substructure hybrid simulation techniques can overcome these scale issues to some extent. Using the software framework OpenFresco, the study involved a continuous exchange of data between a numerical model and a physical specimen. An experimental bearing element is introduced to the HDR bearings, and the remainder of the structure is modeled with beam-column elements for numerical analysis. These hybrid simulation results match the analytical results under the designated earthquake excitation. Therefore, this technique reproduces the seismic performance of a simply supported bridge with HDR bearings. This series of dynamic hybrid simulations of a simply supported bridge provides useful insights into the selection of HDR bearings. The study analyses and discusses the mechanical properties of these HDR bearings when subject to earthquake excitations.
Keywords: Earthquake, Hybrid Simulation, Experimental
Authors: Yoichi Mukai; Ayaka Yokoyama; Kohiro Fushihara; Takashi Fujinaga; and Hideo Fujitani
DOI: 10.3389/fbuil.2020.00145
Abstract: Seismic responses of a single-story RC frame building model under control using an active mass damper (AMD) are demonstrated through a real-time hybrid simulation (RTHS) method. In this study, the RTHS test is carried out by using a hydraulic actuator and a shaking table under a synchronization. Most parts of the target RC frame model are provided as an analytical model for an online computer simulation, and the only single column of the first story is prepared as an experimental substructure. A hydraulic actuator deforms the actual RC column, and uncertainty or nonlinearity of the RC column’s behavior is focused on this RTHS test. At the same time, a control device of AMD is actually tested under a situation of installing it on the target building's floor. The floor response of the target building model is generated using a shaking table. A control motion of the AMD is manipulated based on an online simulation of the entire RC building model. Firstly, a time delay compensation of the hydraulic actuator is considered. Time delay parameters are identified using a combination model of a time lag and a first-order delay. A PID controller and a time series compensator (TSC) are applied to improve actuator performances. Next, the reproducibility of the RTHS test using two-individual actuators is evaluated. The tracking of a restoring force and deformation of the actual RC column specimen generated by the hydraulic actuator and floor motion responses reproduced on the shaking table are investigated. To improve the online numerical simulation based on the measured force responses of the RC column specimen, a high-pass filter (HPF) is applied for a force correction to utilize its phase-lead property. The effect of this HPF force correction is evaluated in both a linear region and a strong nonlinear region of the actual RC column specimen. Finally, the RTHS test results are compared to fully-numerical simulations, and the control effect of the AMD to increase the damping effect for the target RC building model is also investigated.
Keywords: Earthquake, RTHS, UQ, Nonlinear, Experimental
Authors: Amin Maghareh; Yuguang Fu; Herta Montoya; Johnny Condori; Zixin Wang; Shirley Dyke and Arturo Montoya
DOI: 10.3389/fbuil.2020.568742
Abstract: Currently, the lack of (1) a sufficiently integrated, adaptive, and reflective framework to ensure the safety, integrity, and coordinated evolution of a real-time hybrid simulation (RTHS) as it runs, and (2) the ability to articulate and gauge suitable measures of the performance and integrity of an experiment, both as it runs and post-hoc, have prevented researchers from tackling a wide range of complex research problems of vital national interest. To address these limitations of the current state-of-the-art, we propose a framework named Reflective Framework for Performance Management (REFORM) of real-time hybrid simulation. REFORM will support the execution of more complex RTHS experiments than can be conducted today, and will allow them to be configured rapidly, performed safely, and analyzed thoroughly. This study provides a description of the building blocks associated with the first phase of this development (REFORM-I). REFORM-I is verified and demonstrated through application to an expanded version of the benchmark control problem for real-time hybrid simulation.
Keywords: RTHS, Experimental, Benchmark
Authors: Wei Song; Chao Sun; Yanhui Zuo; Vahid Jahangiri; Yan Lu; and and Qinghua Han
DOI: 10.3389/fbuil.2020.00129
Abstract: As an attractive renewable energy source, offshore wind plants are becoming increasingly popular for energy production. However, the performance assessment of offshore wind turbine (OWT) structure is a challenging task due to the combined wind-wave loading and difficulties in reproducing such loading conditions in laboratory. Real-time hybrid simulation (RTHS), combining physical testing and numerical simulation in real-time, offers a new venue to study the structural behavior of OWTs. It overcomes the scaling incompatibilities in OWT scaled model testing by replacing the rotor components with an actuation system, driven by an aerodynamic simulation tool running in real-time. In this study, a RTHS framework for monopile OWTs is proposed. A set of sensitivity analyses is carried out to evaluate the feasibility of this RTHS framework and determine possible tolerances on its design. By simulating different scaling laws and possible error contributors (delays and noises) in the proposed framework, the sensitivity of the OWT responses to these parameters are quantified. An example using a National Renewable Energy Lab (NREL) 5-MW reference OWT system at 1:25 scale is simulated in this study to demonstrate the proposed RTHS framework and sensitivity analyses. Three different scaling laws are considered. The sensitivity results show that the delays in the RTHS framework significantly impact the performance on the response evaluation, higher than the impact of noises. The proposed framework and sensitivity analyses presented in this study provides important information for future implementation and further development of the RTHS technology for similar marine structures.
Keywords: Wind, Wave, RTHS, Experimental
Authors: Thomas Simpson; Vasilis K Dertimanis; and Eleni N. Chatzi
DOI: 10.3389/fbuil.2020.570947
Abstract: We present a method for control in real-time hybrid simulation (RTHS) that relies exclusively on data processing. Our approach bypasses conventional control techniques, which presume availability of a mathematical model for the description of the control plant (e.g., the transfer system and the experimental substructure) and applies a simple plug 'n play framework for tuning of an adaptive inverse controller for use in a feedforward manner, avoiding thus any feedback loops. Our methodology involves (i) a forward adaptation part, in which a noise-free estimate of the control plant's dynamics is derived; (ii) an inverse adaptation part that performs estimation of the inverse controller; and (iii) the integration of a standard polynomial extrapolation algorithm for the compensation of the delay. One particular advantage of the method is that it requires tuning of a limited set of hyper-parameters (essentially three) for proper adaptation. The efficacy of our framework is assessed via implementation on a virtual RTHS (vRTHS) benchmark problem that was recently made available to the community. The attained results indicate that data-driven RTHS may form a competitive alternative to conventional control.
Keywords: Earthquake, RTHS, Algorithms, Experimental, Transfer Systems, Controller Design, Benchmark
Authors: Elif Ecem Bas; and Mohamed A. Moustafa
DOI: 10.3389/fbuil.2020.574965
Abstract: Hybrid simulation (HS) combines analytical modeling with experimental testing to provide a better understanding of both structural elements and entire systems while keeping cost-effective solutions. However, extending real-time HS (RTHS) to bigger problems becomes challenging when the analytical models get more complex. On the other hand, using machine learning (ML) techniques in solving engineering problems across different disciplines keeps evolving and likewise is a promising resource for structural engineering. The main goal of this study is to explore the validity of ML models for conducting RTHS and specifically introduce and validate the necessary communication schemes to achieve this goal. A preliminary study with a simplified linear regression ML model that can be readily implemented in Simulink is presented first to introduce the idea of using metamodels as analytical substructures. However, for ML, commonly used platforms for RTHS such as Simulink and MATLAB have limited capacity when compared to Python for instance. Thus, the main focus of this study was to introduce Python-based advanced ML models for RTHS analytical substructures. Deep long short-term memory networks in Python were considered for advanced metamodeling for RTHS tests. The performance of Python can be enhanced by running the models using high-performance computers, which was also considered in this study. Several RTHS tests were successfully conducted at the University of Nevada, Reno, with Python-based ML algorithms that were run from both local PC and a cluster. The tests were validated through comparisons with the pure analytical solutions obtained from finite element models. The study also explored the idea of embedding the delay compensators within the ML model for RTHS.
Keywords: Earthquake, RTHS, Machine Learning, Algorithms, Experimental
Authors: Christina Insam; Arian Kist; Henri Schwalm; and Daniel J. Rixen
DOI: 10.1016/j.ymssp.2021.107720
Abstract: In many engineering applications, mechanical contact leads to unwanted dynamic phenomena, such as excitation of high frequency modes. To investigate the induced dynamics, systems need to be tested already in the early development stage. Real-Time Hybrid Substructuring (RTHS) is a Hardware-in-the-Loop approach, that enables testing of critical components with realistic boundary impedance. In RTHS, the critical components are tested experimentally, while the remaining system is simulated numerically in a co-simulation. The dynamics of the transfer system, which couples the experimental part with the numerical simulation render the test outcome inaccurate or even make it unstable unless they are compensated for. The aim of this work is to tackle two major shortcomings of RTHS, namely stability and fidelity of RTHS tests. This is achieved by the combined use of Normalized Passivity Control and Iterative Learning Control. Normalized Passivity Control guarantees passivity of the transfer system and Iterative Learning Control improves the actuator tracking performance iteratively in order to increase the fidelity of the test outcome. Furthermore, a convergence condition is proposed for Iterative Learning Control in this setup such that an optimal tuning of the learning law can be achieved. We tested the proposed compensation scheme experimentally for an RTHS test, where contact occurs. A special focus is put on investigating unstable RTHS tests, as their stabilization and accurate testing is a particular challenge. The results show that the test fidelity, which is measured by the relative root-mean-square error, can be improved by a factor of about 6.5. In addition, it is shown that the combination of velocity feedforward, Iterative Learning Control and Normalized Passivity Control improves the tracking and thus the test fidelity even further. The results reveal that the proposed method has the potential not only to overcome the nonlinear effects of friction in the actuator, but also to improve the tracking accuracy in highly dynamic motion tasks. The main advantages over existing compensation techniques are that only little knowledge about the transfer dynamics of the actuator and experimental part is needed and that the implementation is simple. Hence, it is assumed that this method will be of interest for testing with RTHS in many engineering applications, with or without contact.
Keywords: RTHS, Hardware-in-the-loop testing, Iterative Learning Control, Passivity Control, High-fidelity testing, Lag compensation
Authors: Xuguang Wang; Jae-Kwon Ahn; Oh-Sung Kwon; and Robin E. Kim
DOI: 10.1061/(ASCE)ST.1943-541X.0002974
Abstract: The axial capacity and force demand of a steel column are expected to change continuously during a fire incident. In assessing the structural performance in the event of a fire, it is important to monitor both the capacity and force demand at the entire temperature range. Although the axial capacity of steel columns at elevated temperatures can be calculated with closed form-equations in the design codes, limited information is available regarding the changes in force demand due to the time-dependent temperature load. This paper proposes a set of demand-capacity curves for steel columns at elevated temperatures with various initial force and constraint conditions. A series of full-scale steel columns are tested using the hybrid fire simulation (HFS) method to validate the developed demand-capacity curves. The hybrid fire simulation results are also replicated numerically using a finite element model. The test results match the developed curve with minimal calibration. The developed curves can be used as a quick tool to evaluate the axial capacity and force demand of a steel column at elevated temperatures.
Keywords: Fire, Real-Time Hybrid Simulation, Large Scale, Experimental, Case Study
Authors: G. Abbiati; S. Marelli; N. Tsokanas; B. Sudret; and B. Stojadinović
DOI: 10.1016/j.ymssp.2020.106997
Abstract: Hybrid Simulation is a dynamic response simulation paradigm that merges physical experiments and computational models into a hybrid model. In earthquake engineering, it is used to investigate the response of structures to earthquake excitation. In the context of response to extreme loads, the structure, its boundary conditions, damping, and the ground motion excitation itself are all subjected to large parameter variability. However, in current seismic response testing practice, Hybrid Simulation campaigns rely on a few prototype structures with fixed parameters subjected to one or two ground motions of different intensity. While this approach effectively reveals structural weaknesses, it does not reveal the sensitivity of structure’s response. This thus far missing information could support the planning of further experiments as well as drive modeling choices in subsequent analysis and evaluation phases of the structural design process. This paper describes a Global Sensitivity Analysis framework for Hybrid Simulation. This framework, based on Sobol’ sensitivity indices, is used to quantify the sensitivity of the response of a structure tested using the Hybrid Simulation approach due to the variability of the prototype structure and the excitation parameters. Polynomial Chaos Expansion is used to surrogate the hybrid model response. Thereafter, Sobol’ sensitivity indices are obtained as a by-product of polynomial coefficients, entailing a reduced number of Hybrid Simulations compared to a crude Monte Carlo approach. An experimental verification example highlights the excellent performance of Polynomial Chaos Expansion surrogates in terms of stable estimates of Sobol’ sensitivity indices in the presence of noise caused by random experimental errors.
Keywords: Hybrid simulation, Global sensitivity analysis, Sobol’ indices, Surrogate modeling, Polynomial chaos expansion
Authors: Christina Insam; and Daniel J. Rixen
DOI: 10.1007/s40799-021-00466-0
Abstract: Real-Time Hybrid Substructure (RTHS) testing is a commonly used method to investigate the dynamical influence of a component on a mechanical system. In RTHS, a part of the dynamical system is tested experimentally, while the remaining structure is simulated numerically in a co-simulation. There are several error sources in the RTHS loop that distort the test outcome. To investigate the reliability of the test, the fidelity of the test must be quantified. In many engineering applications, however, there is no reference solution available to which the test outcome can be validated against. This work reviews currently existing accuracy measures used in RTHS. Furthermore, using Artificial Neural Networks (ANN) to predict the fidelity of the RTHS test outcome when no reference solution is available is proposed. Appropriate input features for the network, such as dynamic properties of the system and existing error indicators, are discussed. ANN training was performed on a data set from a virtual RTHS (vRTHS) simulation of a dynamical system with contact. The training process was successful, meaning that the correlation between the ANN prediction and the true fidelity value was > 99 %. Then, the network was applied to data of experimental RTHS tests of the same dynamical system and achieved a correlation of 98 %, which proves that the relation found by the ANN captured the relation between the chosen input features and the error measure. The application of the trained ANN to data from a linear vRTHS test revealed that further improvement of the network and the choice of input features is necessary. This work suggests that ANNs could be a meaningful tool to predict the fidelity of the RTHS test outcome in the absence of a reference solution, especially if more data from different RTHS tests were aggregated to train them.
Keywords: Real-time hybrid simulation, Artificial neural networks, Fidelity, Accuracy measures
Authors: Christina Insam; L.D. Hashan Peiris; and Daniel J. Rixen
DOI: 10.1007/s40435-021-00790-8
Abstract: Mechanical contact occurs in many engineering applications. Contact dynamics can lead to unwanted dynamic phenomena in mechanical systems. Hence, it would be desirable to investigate the influence of contact dynamics on a dynamical system already in the development stage. An appropriate method is Hardware-in-the-loop (HiL) on mechanical level. However, the coupling procedure in HiL is prone to stability problems and previous studies revealed that HiL tests of systems with contact are even more challenging, as the system dynamics change rapidly when contact occurs. Passivity-based control schemes, well-known from teleoperation, have recently been used to stabilize HiL simulations of systems with continuous dynamics. Here, we investigate the applicability of Normalized Passivity Control to HiL tests of a one-dimensional mass-spring-damper system experiencing contact. Experimental results reveal that this kind of passivity control keeps the test stable and also improves the test fidelity. This research is an important first step in using passivity control for stable and safe hybrid simulation of complex systems with contact using HiL approaches.
Keywords: Hardware-in-the-loop simulation, Real-time hybrid simulation, Passivity-based control, Contact dynamics
Authors: Christina Insam; Lisa-Marie Ballat; Felix Lorenz; and Daniel J. Rixen
DOI: 10.3390/app11209492
Abstract: For a targeted development process of foot prostheses, a profound understanding of the dynamic interaction between humans and prostheses is necessary. In engineering, an often employed method to investigate the dynamics of mechanical systems is Hardware-in-the-Loop (HiL). This study conducted a fundamental investigation of whether HiL could be an applicable method to study the dynamics of an amputee wearing a prosthesis. For this purpose, a suitable HiL setup is presented and the first-ever HiL test of a prosthetic foot performed. In this setup, the prosthetic foot was tested on the test bench and coupled in real-time to a cosimulation of the amputee. The amputee was modeled based on the Virtual Pivot Point (VPP) model, and one stride was performed. The Center of Mass (CoM) trajectory, the Ground Reaction Forces (GRFs), and the hip torque were qualitatively analyzed. The results revealed that the basic gait characteristics of the VPP model can be replicated in the HiL test. Still, there were several limitations in the presented HiL setup, such as the limited actuator performance. The results implied that HiL may be a suitable method for testing foot prostheses. Future work will therefore investigate whether changes in the gait pattern can be observed by using different foot prostheses in the HiL test.
Keywords: Real-time hybrid simulation, Nonlinear Specimens, Experimental
Authors: Ge Ou; Ge Yang; Shirley Dyke; and Bin Wu
DOI: 10.3389/fbuil.2020.00103
Abstract: In hybrid simulation, response time history measured from an experimental substructure can be utilized to identify the model associated with the tested specimen in real time. To improve the modeling accuracy, the updated model parameters can substitute the initial parameters of similar components (as the tested specimen) that reside in the numerical substructure. In this study, a detailed investigation into the fidelity improvement using model updating in hybrid simulation has been carried out. This study has focused on both local and global assessment of hybrid simulation with model updating (HSMU) by comparing HSMU with conventional simulation and shake table testing. In the local assessment, the updating efficiency with different nonlinemodels (one phenomenological model and one FEM model) have been illustrated; in the global assessment, the HSMU response time histories have been compared to experimental shake table testing. Observations and comments on model selection, parameter convergence, and time and frequency domain performance of HSMU have been provided.
Keywords: Earthquake, Real-time hybrid simulation, Nonlinear specimens, Model Updating, Experimental
Authors: Hongwei Li; Aming Maghareh; Herta Montoya; Johnny Wilfredo Condori Uribe; Shirley J. Dyke; and Zhaodong Xu
DOI: 10.1016/j.ymssp.2020.107364
Abstract: Real-time hybrid simulation (RTHS) is a novel cyber-physical testing technique for investigating especially large or complicated structural systems. Controllers are required to compensate for the dynamics of transfer systems that emulate the interactions between the physical and numerical substructures. Thus, both the stability and accuracy of RTHS testing highly depend on the effectiveness of the control strategy. This paper proposes a robust sliding mode controller (SMC) as a transfer system control strategy in RTHS. A design procedure of the SMC control strategy is presented. The benchmark problem on RTHS control is utilized for demonstration and validation of SMC for this class of problems. Virtual RTHS results show that the SMC strategy significantly improves the performance and robustness of RTHS testing.
Keywords: Earthquake, Real-time hybrid simulation, Controller Design, Benchmark
Authors: Jacob P. Waldbjoern; Amin Maghareh; Ge Ou; Shirley J. Dyke; and Henrik Stang
DOI: 10.1016/j.engstruct.2021.112308
Abstract: For a targeted development process of foot prostheses, a profound understanding of the dynamic interaction between humans and prostheses is necessary. In engineering, an often employed method to investigate the dynamics of mechanical systems is Hardware-in-the-Loop (HiL). This study conducted a fundamental investigation of whether HiL could be an applicable method to study the dynamics of an amputee wearing a prosthesis. For this purpose, a suitable HiL setup is presented and the first-ever HiL test of a prosthetic foot performed. In this setup, the prosthetic foot was tested on the test bench and coupled in real-time to a cosimulation of the amputee. The amputee was modeled based on the Virtual Pivot Point (VPP) model, and one stride was performed. The Center of Mass (CoM) trajectory, the Ground Reaction Forces (GRFs), and the hip torque were qualitatively analyzed. The results revealed that the basic gait characteristics of the VPP model can be replicated in the HiL test. Still, there were several limitations in the presented HiL setup, such as the limited actuator performance. The results implied that HiL may be a suitable method for testing foot prostheses. Future work will therefore investigate whether changes in the gait pattern can be observed by using different foot prostheses in the HiL test.
Keywords: Earthquake, Real-time hybrid simulation, Algorithms, Experimental
Authors: Ramin Rabiee; and Yunbyeong Chae
DOI: 10.1177%2F1045389X221079680
Abstract: The transmissibility-based semi-active (TSA) controller was developed in the existing study by the authors, which can effectively enhance the performance of base-isolated buildings under both strong long- and short-period earthquake ground motions. Since the performance of the TSA controller was only evaluated with numerical simulation in the existing study, this paper further validates its performance experimentally by conducting real-time hybrid simulation (RTHS). A three-story base isolated building was designed based on a simplified design procedure, where the base isolation system of the building consisted of three different devices, that is, a magneto-rheological (MR) damper, rubber bearing, and linear bearings. The base isolation system was experimentally tested with the MR damper controlled by the TSA controller, and the building superstructure was analytically modeled. It was shown that the TSA controller makes the system damping high under long-period ground motions and low under short-period ground motions, which performed uniquely as intended. As a result, the isolator displacement was effectively reduced under long-period ground motions, while the story drift and acceleration responses were also reduced under short-period ground motions, all of which are difficult to achieve at the same time using passive damping only.
Keywords: Earthquake, Real-time hybrid simulation, Nonlinear Specimens, Experimental, Controller Design
Authors: Hossein Mostafaei
DOI: 10.1016/j.firesaf.2013.02.005
Abstract: A new performance-based assessment approach for structures in fire, referred to as hybrid fire testing (HFT) method, is presented in this article. The HFT was developed based on a sub-structuring method, by dividing the whole structure into two substructures, one being tested in a furnace and one being simulated by a computer. This represents a form of “hardware-in-the-loop” simulation. Using HFT, the performance of the whole building can be evaluated at a very reasonable cost, significantly less than the cost of the direct whole building test. More reliable results than the prescriptive method can also be achieved with comparable and even more comprehensive results than that of a direct full-scale test. A 6-storey reinforced concrete building was designed, as a prototype for application of the hybrid fire testing approach. Two fire scenario examples were considered; a 6-storey building with a fire compartment on the first floor, in the center of the building and a 6-storey building with a fire compartment on the third floor. The two substructures for these two HFT scenarios were; one the column in the fire compartment and two the rest of the building. This paper includes the description of the hybrid testing methodology, details of the 6-storey building prototype and the methodology verification. Using the HFT approach, various scenarios could be explored to couple modeling and testing globally. This may also provide the possibility of running one test in a testing facility, e.g. NRC's, and running the analysis remotely at a different location. This would make furnace facilities more accessible to the research communities around the globe.
Keywords: Fire resistance, Performance-based design, Hybrid test, Full-scale test, Test and analysis/simulation, Hybrid fire testing
Authors: Hossein Mostafaei
DOI: 10.1016/j.firesaf.2012.12.003
Abstract: This paper presents the results for application and implementation of the hybrid fire testing (HFT) approach, developed previously for performance assessment of the structure in fire. The HFT carried out by means of both computer simulation and experimentation using the National Research Council Canada's (NRC) testing facilities in Ottawa. The test specimen was a full-scale 6-storey building structure with a fire compartment scenario on the main floor of the building. Using the HFT, the column in the designated fire compartment was exposed to the fire in a column furnace and the rest of the building was simulated using a numerical modeling, simultaneously. The methodology of the HFT and its numerical verifications were developed and described in a previous paper. This paper includes application of the HFT and some of results for fire structural performance of the whole 6-storey building. It also includes results of a separate, benchmark, column specimen with identical specifications, tested in fire using the traditional prescriptive fire resistance test method. The HFT was carried out successfully. The results indicated that the hybrid fire testing method would provide more realistic fire endurance evaluation than the prescriptive method due to including the effects from the rest of the building on the column specimen during the test.
Keywords: Fire resistance, Performance-based design, Hybrid test, Full-scale test, Test and analysis/simulation, Hybrid fire testing
Authors: Catherine A. Whyte; Kevin R. Mackie; and Bozidar Stojadinovic
DOI: 10.1061/(ASCE)ST.1943-541X.0001346
Abstract: A new thermomechanical hybrid simulation method is proposed that extends the mechanical hybrid simulation method by including thermal degrees of freedom and temperature loads. The thermomechanical hybrid simulation method was implemented in the OpenSees and OpenFresco frameworks. Modifications to enable this new capability centered on incorporating the temperature degrees of freedom in the hybrid model domain, and on developing new OpenFresco objects and a test execution strategy to simultaneously control the structural elements of the experimental setup, the thermal loads, and the mechanical loads. The implementation of the thermomechanical method at the ETH Zürich IBK Structural Testing Laboratory was verified and validated using a simple two-element hybrid model. The responses of the model to a force ramp, applied to the full structure, and a scaled version of the ISO 834 standard fire curve, applied to the experimental element, were obtained in two simulations—one conducted using an explicit and the other using an implicit integration scheme. The tests yield very similar results, and both simulations closely match the theoretical solution.
Keywords: Fire resistance, Thermomechanical, Hybrid test, Full-scale test, Test and analysis/simulation, Hybrid fire testing
Authors: Giuseppe Abbiati; Oreste Bursi; Bozidar Stojadinovic; Nicola Tondini; and Catherine Whyte
DOI: http://hdl.handle.net/2117/191131
Abstract: The present paper presents all research activities focused on the development of a pure thermal hybrid simulator (THS). In detail, the need for a rigorous coupling is investigated, i.e. temperatures are sent from the numerical substructure (NS) to the physical substructure (PS) and interface heat fluxes are sent back from the PS to the NS. In this respect, a realistic benchmark case study is presented. It consists of a 2D truss bridge where a single truss element is “physically” substructured. In the current preliminary phase, an additional multiphysics FE code, COMSOL, is utilized to simulate the thermal response of this “experimental” substructure inside the electric furnace. In detail, two variants of the same case study are presented and characterized by two significantly different average thermal diffusivities. This approach provides a realistic insight into the capabilities of THS. Moreover, the present study paves the way for the implementation of a fully coupled thermomechanical hybrid simulation (TMHS), which account for indirect actions owing to restrained thermal deformations on the hot NS.
Keywords: Fire resistance, Thermomechanical, Hybrid test, Test and analysis/simulation, Hybrid fire testing
Authors: Giuseppe Abbiati; Catherine Whyte; Vasilis Dertimanis; and Bozidar Stojadinovic
DOI: http://hdl.handle.net/20.500.11850/264494.1
Abstract: In the last two decades, hybrid simulation has received increasing attention from the earthquake engineering community as a tool for simulating the nonlinear dynamic response of large structural systems in facilities with limited capacities. The quality of the simulation strongly depends of the correct application of the interface boundary conditions between the numerical and the physical subdomains. Nevertheless, the need for reducing costs and efforts related the experimental setup usually forces the partial relaxation of coupling conditions e.g., discarding interface rotational degrees-of-freedom. In this scenario, re-usable multi-axis subassemblage testing loading systems represent a convenient trade-off between achievable coupling fidelity degree and experiment cost. Along this line, this paper revisits state-of-the-art setups and presents our recent developments on this direction at the Swiss Federal Institute of Technology (ETH) in Zurich.
Keywords: Hybrid Simulation, Kriging Metamodeling, Gaussian Process, Active Learning, Adaptive Experimental Design
Authors: Adel E. Abdelnaby; Thomas M. Frankie; Amr S. Elnashai; Billie F. Spencer; Daniel A. Kuchma; Pedro Silva; and Chia-Ming Chang
DOI: 10.1016/j.engstruct.2014.04.009.
Abstract: Reinforced concrete (RC) bridge piers are subjected to combined loading conditions resulting from complex earthquake ground motions coupled with irregular geometry and asymmetry of the bridge structure. Furthermore, the influence of the assumptions and simplifications made in modeling irregular and curved bridges on the reliability of their resulting response data is still not fully known. For that purpose, in this paper a hybrid simulation test is conducted on a curved four-span bridge. This test accounts for the three-dimensional (3D) system-level interaction between the three experimental piers in two testing facilities with the numerical models of the deck, restraints and abutments. Prior to the hybrid simulation, a detailed numerical finite element, fiber-based model of the whole bridge system is established. The analytical predictions of this model are then used for comparison with the hybrid simulation test results. Discrepancies between the numerical and experimental results of the bridge piers response are highlighted and deficiencies in the numerical model assumptions are discussed. A rigorous numerical model calibration procedure is then followed to adjust for the initial modeling assumptions and improve the bridge model overall response. This study has proven that some modeling assumptions that are widely used in seismic analysis of bridge structures are unrealistic and therefore may lead to inaccurate results.
Keywords: Curved Bridge, Hybrid Simulation, Numerical Model Calibration, Combined Actions, Multi-Directional Loading
Authors: Ali Y. Al-Attraqchi; M. Javad Hashemi; and Riadh Al-Mahaidi
DOI: 10.1007/s10518-020-00871-7
Abstract: This paper presents the application of multi-axis hybrid simulation for evaluating the seismic response of a rigid-frame bridge structure constructed with concrete-filled steel tube (CFST) columns subjected to combined horizontal and vertical ground motions. These types of bridges are believed to have superior seismic performance and better ability to withstand collapse when subjected to extreme multi-directional seismic loads. The case-study hybrid model was a 1:3 scaled bridge structure with three spans and double-column bents. The experimental element consisted of one CFST column while the rest of the bridge elements were modelled numerically in the computer. Two popular cross-section shapes of circular and square CFST columns were tested and compared. The structure was subjected to the horizontal (longitudinal) and vertical components of the Northridge ground motion with five increasing intensity levels to cover all scenarios ranging from frequent to very rare events during the lifecycle of the structure. A state-of-the-art hybrid testing facility, referred to as the multi axis substructure testing system, was used to simulate complex boundary effects on the physical specimen using mixed load/deformation modes. The bridge columns showed great levels of ductility and no sign of severe damage or loss of stability, while they were subjected to large axial force variations and lateral deformation demands during hybrid simulations. The superior seismic performance of CFST elements highlights their benefit in construction of more resilient bridges, particularly those with the vital roles in post-disaster operations.
Keywords: Multi-Axis Hybrid Testing, Concrete-Filled Steel Tube, Vertical Ground Motions, Resilient Bridges
Authors: Riadh Al-Mahaidi; M Javad Hashemi; Robin Kalfat; Graeme Burnett; and John Wilson
DOI: 10.1007/978-981-10-5867-7
Abstract: This book describes the multi-axis substructure testing (MAST) system, a simulator developed at Swinburne University of Technology, Australia, which provides state-of-the-art technology for large-scale hybrid testing of structures under realistic scenarios depicting extreme events. The book also demonstrates the responses of physical specimens while they serve as part of the virtual computer model of the full structure subjected to extreme dynamic forces. Experimental studies using the MAST system are expected to enhance design and construction methods and significantly improve the repair and retrofitting of structures endangered by natural disasters and man-made hazards, providing a direct benefit to society by improving public safety and the resilience of the built environment. An additional benefit is increased sustainability in the form of reduced direct and indirect economic losses and social and environmental impacts in the face of extreme events. This book will be of interest to researchers and advanced practitioners in the fields of structural earthquake engineering, geotechnical earthquake engineering, engineering seismology, and experimental dynamics, including seismic qualification.
Keywords: Six-Degrees-of-Freedom (6-DOF) Hybrid Testing, Hybrid Simulation, Large-Scale Structures Testing, Extreme Loads, Collapse Assessment, Multi-Axis Substructure Testing (MAST), Quasi-Static Test, Collapse Simulation, Strong Wall, Steel Crosshead
Authors: Anthony Blakeborough; Martin S. Williams; Antony P. Darby; and D. M. Williams
DOI: 10.1098/rsta.2001.0877
Abstract: Full–scale dynamic testing of civil engineering structures is extremely costly and difficult to perform. Most test methods therefore involve either a reduction in the physical scale or an extension of the time–scale. Both of these approaches can cause significant difficulties in extrapolating to the full–scale dynamic behaviour, particularly when the structure responds nonlinearly or includes highly rate–dependent components such as dampers. Real–time substructure testing is a relatively new method which seeks to avoid these problems by performing tests on key elements of the structure at full or large scale, with the physical test coupled in real time to a numerical model of the surrounding structure. The method requires a high performance of both the physical test equipment and the numerical algorithms. This paper first reviews the development of structural test methods and the emergence of real–time substructure testing. This is followed by a brief description of the equipment that is needed to implement a substructure test. Several novel developments in the numerical algorithms used in real–time substructure testing are presented, including a new, fast algorithm which allows nonlinear response of the surrounding structure to be computed in real time. Results are presented from a variety of tests which demonstrate the performance of the system at small and large scale, with either linear or nonlinear test specimens, and with varying numbers of degrees of freedom passed between the physical and numerical substructures. Finally, the usefulness and possible applications of the test method are discussed.
Keywords: Six-Degrees-of-Freedom (6-DOF) Hybrid Testing, Hybrid Simulation, Large-Scale Structures Testing, Extreme Loads, Collapse Assessment, Multi-Axis Substructure Testing (MAST), Quasi-Static Test, Collapse Simulation, Strong Wall, Steel Crosshead
Authors: Paul A. Bonnet; C. N. Lim; Martin S. Williams; Anthony Blakeborough; Simon A. Neild; David Paul Stoten; and Colin A. Taylor
DOI: 10.1002/eqe.628
Abstract: Real-time hybrid testing is a promising technique for experimental structural dynamics, in which the structure under consideration is split into a physical test of key components and a numerical model of the remainder. The physical test and numerical analysis proceed in parallel, in real time, enabling testing of critical elements at large scale and at the correct loading rate. To date most real-time hybrid tests have been restricted to simple configurations and have used approximate delay compensation schemes. This paper describes a real-time hybrid testing approach in which non-linearity is permitted in both the physical and numerical models, and in which multiple interfaces between physical and numerical substructures can be accommodated, even when this results in very stiff coupling between actuators. This is achieved using a Newmark explicit numerical solver, an advanced adaptive controller known as MCSmd and a multi-tasking strategy. The approach is evaluated through a series of experiments on discrete mass-spring systems.
Keywords: Real-Time Testing, Substructuring, Adaptive Control
Authors: Rui M. Botelho and Richard E. Christenson
DOI: 10.1007/978-3-319-15209-7_1
Abstract: Real-time hybrid substructuring (RTHS) is a relatively new method of vibration testing for characterizing the system-level performance of physical components or substructures. With RTHS, the coupled system is partitioned into physical and numerical substructures and interfaced together in real-time as cyber-physical system similar to hardware-in-the-loop testing. Control actuation and sensing is used to enforce the compatibility and equilibrium conditions between the physical and numerical substructures. Since RTHS involves a feedback loop, the frequency-dependent magnitude and inherent time delay of the actuator dynamics can introduce inaccuracy and instability. This paper presents a robust stability and performance analysis method for multi-actuator RTHS based on robust stability theory for multiple-input-multiple-output (MIMO) feedback control. This analysis method involves casting the actuator dynamics as a multiplicative uncertainty and applying the small gain theorem to derive the sufficient conditions for robust stability and performance. The attractive feature of this robust stability and performance analysis method is that it accommodates linearized modeled or measured frequency response functions for both the physical substructure and actuator dynamics.
Keywords: Experimental Structural Dynamics, Real-Time Hybrid Testing, Dynamic Substructuring, Hardware-In-The-Loop Testing, Robust Stability, Feedback Control Systems
Authors: Stathis N. Bousias
DOI: 10.1155/2014/825692
Abstract: Advances in the area of structural testing have in recent years led to hybrid simulation, that is, the advanced structural experimental method that encompasses the traditional pseudodynamic testing method and relies on substructuring to offer the advantage of combining the actual experimental testing of selected parts of the structure to the numerical treatment of the rest. The experimental part usually involves simplified test setups and structural elements with few degrees of freedom. Thus, issues of cross-coupling present in testing MDOF structures have not been treated adequately so far. In addition, it has been realized that when it comes to testing very stiff structures, in which the above phenomena are accentuated, further problems arise in relation to the quality of actuator control (accuracy of imposed displacements and stability of the test process). Few studies have focused on these issues, thus necessitating more work in the future. The present study provides an overview of the approaches that have been adopted so far, reports on recent advancements, and raises the points in which more research is needed.
Keywords: Structural Testing, Pseudodynamic Testing, Substructuring, Stiff Structures
Authors: Chia-Ming Chang; Thomas M. Frankie; Billie F. Spencer; and Daniel A. Kuchma
DOI: 10.1080/13632469.2014.962670
Abstract: This study proposes a high-precision positioning correction method for multiple degree-of-freedom loading units in hybrid simulation. These loading units can impose inaccurate displacements to the specimens due to the elastic deformation at the reaction wall or connections. To compensate for these displacement errors, an online correction method adjusts the displacement command by the difference between the target and achieved displacement. This correction method also accompanies an accurate 6DOF monitoring system to detect the displacement errors. Two examples of hybrid simulation tests are provided to demonstrate the precise displacements attained on the specimens through this control method.
Keywords: Elastic Deformation, 6DOF Positioning Control, 6DOF Displacement Monitoring, Hybrid Simulation, Four-span Curved Bridge
Authors: Cheng Chen; James M. Ricles; Ian C. Hodgson; and Richard Sause
DOI: https://www.iitk.ac.in/nicee/wcee/article/14_S16-01-007.PDF
Abstract: Observations during past earthquakes have demonstrated the seismic vulnerability of nonstructural components. Damage to these components can significantly reduce the functionality of essential facilities. Real-time hybrid simulation combines experimental testing and numerical simulation, and therefore provides an excellent technique for the dynamic testing of complete systems rather than testing components or subsystems. In this paper, a real-time multi-directional hybrid simulation of a system of nonstructural components is presented. In the simulation, a building piping system in a three-story moment resistant frame is subjected to bi-directional earthquake ground motions. The pressurized piping on the third story is selected as the experimental substructure, while the rest of the structure is modeled analytically. The Lehigh University Real-Time Multi-Directional Seismic Simulation Facility is used for the study. To ensure accuracy and stability during the simulation, the newly developed unconditionally stable explicit CR integration algorithm and inverse compensation method for actuator delay are used. The two horizontal components of the 1994 Northridge earthquake ground motion recorded at Canoga Park are scaled to the MCE seismic hazard level. Real-time hybrid simulation is performed to evaluate the seismic performance of the components of the piping system, including the bracing, joints, and piping members. The simulation results indicate that adequate piping joints and carefully designed bracing can enable the nonstructural piping system to perform well under strong earthquakes. The experimental study presented in this paper demonstrates the application of real-time hybrid simulation to the seismic testing of nonstructural components.
Keywords: Real-Time Hybrid Simulation, Nonstructural Component, Nonstructural System, Actuator Delay Compensation, Integration Algorithm
Authors: Antony P. Darby; Martin S. Williams; and Anthony Blakeborough
DOI: 10.1061/(ASCE)0733-9399(2002)128:12(1276)
Abstract: Real-time substructure testing is a method for establishing the dynamic behavior of structural systems. The method separates a complex structure into physical and numerically modeled substructures, which interact in real-time allowing time-dependent nonlinear behavior of the physical specimen to be accurately represented. Displacements are applied to the physical specimen using hydraulic actuators and the resulting measured forces are fed back to the numerical substructure. This feedback loop is implemented as a time-stepping routine. One of the key factors in obtaining reliable results using this method is the accurate compensation of the delayed response of the actuator. If this is not accounted for, instability of the feedback loop is likely to occur. This paper presents a method for estimating the delay while a test is in progress and accurately compensating for it during the test. The stability of both linear and nonlinear single-actuator systems is examined and the behavior of twin-actuator systems controlling two degrees-of-freedom at the substructure interface is presented. The effectiveness of the method is clearly demonstrated by comparisons between experimental and theoretical behavior.
Keywords: Real-Time Hybrid Simulation, Nonstructural Component, Nonstructural System, Actuator Delay Compensation, Integration Algorithm.
Authors: Dennis de Klerk; Daniel J. Rixen; and Sven N. Voormeeren
DOI: https://doi.org/10.2514/1.33274
Abstract: Four decades after the development of the first dynamic substructuring techniques, there is a necessity to classify the different methods in a general framework that outlines the relations between them. In this paper, a certain vision on substructuring methods is proposed, by recalling important historical milestones that allow us to understand substructuring as a domain decomposition concept. Thereafter, based on the dual and primal assembly of substructures, a general framework for the classification of the methods is presented. This framework allows us to indicate how the various classes of methods, proposed along the years, can be derived from a clear mathematical description of substructured problems. Current bottlenecks in experimental dynamic substructuring, as well as solution; found in literature, will also be briefly discussed.
Keywords: Dynamic Substructuring, Domain Decomposition
Authors: Yang Ding; Rui MaY; un-Dong Shi; and Zhong-XianLi
DOI: https://doi.org/10.1016/j.marstruc.2017.12.004
Abstract: The cross-sea bridges that located in earthquake-prone areas have the potential to be subjected to earthquake and wave-current action simultaneously during their construction and service period. In order to investigate the dynamic response of the pier under combined earthquake and wave-current action, a series of model tests of scale 50:1 was carried out using the Earthquake, Wave and Current Joint Simulation System. Four main tests were conducted under various water levels, including white noise tests, independent earthquake tests, independent wave-current tests and combined earthquake and wave-current tests. The effect of wave-current action on the seismic responses of the pier and the distribution law of hydrodynamic pressure along the height of the pier under various load conditions are determined. The test results show that the existence of water decreases the natural frequencies of the pier. The peak dynamic responses of the pier in water under independent earthquake action are mostly larger than those without water. When the earthquake excitation is moderate and the wave-current action is relatively severe, the dynamic responses of the pier under independent wave-current action are comparable to those under independent earthquake action, and the effect of wave-current action on the seismic responses of the pier under combined earthquake and wave-current action is great and can not be ignored. Therefore, it is necessary to consider the combined action of earthquake and wave-current in bridge design under this circumstance, and the effect of long-period earthquake on bridges should be considered.
Keywords: Bridge Pier, Earthquake, Wave-Current, Combined Action, Distribution of Hydrodynamic Pressure
Authors: Baiping Dong; Richard Sause; and James M. Ricles
DOI: 10.1002/eqe.2572
Abstract: This paper presents real-time hybrid earthquake simulation (RTHS) on a large-scale steel structure with nonlinear viscous dampers. The test structure includes a three-story, single-bay moment-resisting frame (MRF), a three-story, single-bay frame with a nonlinear viscous damper and associated bracing in each story (called damped braced frame (DBF)), and gravity load system with associated seismic mass and gravity loads. To achieve the accurate RTHS results presented in this paper, several factors were considered comprehensively: (1) different arrangements of substructures for the RTHS; (2) dynamic characteristics of the test setup; (3) accurate integration of the equations of motion; (4) continuous movement of the servo-controlled hydraulic actuators; (5) appropriate feedback signals to control the RTHS; and (6) adaptive compensation for potential control errors. Unlike most previous RTHS studies, where the actuator stroke was used as the feedback to control the RTHS, the present study uses the measured displacements of the experimental substructure as the feedback for the RTHS, to enable accurate displacements to be imposed on the experimental substructure. This improvement in approach was needed because of compliance and other dynamic characteristics of the test setup, which will be present in most large-scale RTHS. RTHS with ground motions at the design basis earthquake and maximum considered earthquake levels were successfully performed, resulting in significant nonlinear response of the test structure, which makes accurate RTHS more challenging. Two phases of RTHS were conducted: in the first phase, the DBF is the experimental substructure, and in the second phase, the DBF together with the MRF is the experimental substructure. The results from the two phases of RTHS are presented and compared with numerical simulation results. An evaluation of the results shows that the RTHS approach used in this study provides a realistic and accurate simulation of the seismic response of a large-scale structure with rate-dependent energy dissipating devices.
Keywords: RTHS, Earthquake Simulations, Nonlinear Viscous Dampers, Hydraulic Actuators
Authors: Yuanfeng Duan; Junjie Tao; Hongmei Zhang; Sumei Wang; and Chungbang Yun
DOI: 10.1002/stc.2277
Abstract: The numerical substructure of a real-time hybrid simulation (RTHS) has been considerably simplified through condensation methods to relieve the burden incurred by computation. However, this simplification severely limits the application of RTHS to structures whose numerical parts are complex and require a large number of degrees of freedom (DOFs) to model. Thus, in this study, a vector form intrinsic finite element (VFIFE) analysis is introduced to RTHS with numerical substructures containing a large number of DOFs. A field programmable gate array (FPGA) is also employed to speed-up the numerical simulation of the VFIFE through parallel computing in RTHS. The characteristics of this parallel RTHS platform using VFIFE and FPGA are discussed in detail in this paper. A simple RTHS was carried out to verify the feasibility of this new platform, followed by a complex virtual RTHS to show its powerful computational capability.
Keywords: RTHS, Vector Form Intrinsic Finite Element, Numerical Substructure, Field Programmable Gate Array
Authors: Shirley J. Dyke; Billie F. Spencer; P. Quast; and M. K. Sain
DOI: 10.1061/(ASCE)0733-9399(1995)121:2(322)
Abstract: Most of the current research in the field of structural control for mitigation of responses due to extreme environmental loads does not directly account for the effects of control-structure interaction and actuator/sensor dynamics in analysis and design. The importance of including control-structure interaction when modeling a control system is discussed herein, and a general framework within which one can study its effect on protective systems is presented. A specific model for hydraulic actuators typical of those used in many protective systems is developed, and a natural velocity feedback link is shown to exist which tightly couples the dynamics of the hydraulic actuator to the dynamics of the structure to which it is attached. Experimental verification of this model is given. Numerical examples are provided that use seismically excited structures configured with active bracing, active tendon, and active mass driver systems. These examples show that accounting for control-structure interaction and actuator dynamics can significantly improve the performance and robustness of a protective system.
Keywords: Extreme Environmental Loads, Control-Structure Interaction, Actuator/Sensor Dynamics, Velocity Feedback, Protective Systems
Authors: Herta Montoya, Shirley J Dyke, Christian E Silva, Amin Maghareh, Jaewon Park, Davide Ziviani
DOI: 10.2514/1.J062857
Abstract: Real-time hybrid simulation (RTHS) is an enabling technology that has transformed engineering experimentation and helped researchers expand modeling capabilities. However, breakthroughs are necessary to expand the range of hybrid simulation methods and, thus, enable experiments with loading conditions representing multiple hazards. This paper discusses the development of a new thermomechanical RTHS framework and a systematic approach to determining RTHS control requirements. First, the framework is established using a representative finite element model of a layered structural system subjected to thermal loading. A complete two-layer system model serves as the reference system, and it is then partitioned into a numerical layer and an experimental layer that share interface conditions. Next, a thermal actuator is introduced to impose dynamic thermal loading on the experimental subsystem, serving as a transfer system. Finally, control and performance metrics are defined to evaluate the realization of interface boundary conditions and map this to the RTHS execution. Through an illustrative example considering the influence of temperature on a lunar habitat, we demonstrate how to establish controller requirements for RTHS and demonstrate that this approach can be used to conduct RTHS on structures with thermomechanical loading.
Keywords: Convection, Heat Transfer Coefficient, Transient Heat Conduction, Thermophysical Properties, Thermal Transfer System, Thermal Analysis, Real-Time Hybrid Simulation
Authors: Amirali Najafi, Gaston Fermandois, Shirley J Dyke, Billie F. Spencer
DOI: 10.1016/j.engstruct.2022.115284
Abstract: This paper reviews the conceptual and technical advances in multi-actuator dynamic loading in modern structural testing. In particular, a focus is given to the developments and challenges in multi-axial hybrid simulation (maHS) and multi-axial real-time hybrid simulation (maRTHS), where a specimen is subjected to multi-directional dynamic loading by interacting with a numerical simulation of its surrounding structural subsystems and components. This review introduces the general framework for maHS and maRTHS, describing substructuring techniques, loading equipment, and nonlinear kinematics. In particular, the process of dynamic compensation for multi-actuator loading assemblies in maRTHS is explored. Different compensation architectures in the task (Cartesian) and joint (actuator) spaces are covered, and each alternative is assessed on its own merits for the dynamic synchronization of multi-actuator loading platforms. Finally, current challenges in maHS and maRTHS testing are identified, with recommendations for future research endeavors for the scientific community.
Keywords: Literature review, Hybrid simulation, Structural testing, Substructuring, Multiple actuators, Nonlinear kinematics, Specimen-actuator interaction, Dynamic compensation
Authors: Johnny Condori, Manuel Salmeron, Edwin Patino, Herta Montoya, Shirley J. Dyke, Christian Silva, Amin Maghareh, Mehdi Najaria, Arturo Montoya
DOI: 10.3389/fbuil.2023.1270996
Abstract: Advancing RTHS methods to readily handle multi-dimensional problems has great potential for enabling more advanced testing and synergistically using existing laboratory facilities that have the capacity for such experimentation. However, the high internal coupling between hydraulics actuators and the nonlinear kinematics escalates the complexity of actuator control and boundary condition tracking. To enable researchers in the RTHS community to develop and compare advanced control algorithms, this paper proposes a benchmark control problem for a multi-axial real-time hybrid simulation (maRTHS) and presents its definition and implementation on a steel frame excited by seismic loads at the base. The benchmark problem enables the development and validation of control techniques for tracking both translation and rotation degrees of freedom of a plant that consists of a steel frame, two hydraulic actuators, and a steel coupler with high stiffness that couples the axial displacements of the hydraulic actuators resulting in the required motion of the frame node. In this investigation, the different components of this benchmark were developed, tested, and a set of maRTHS were conducted to demonstrate its feasibility in order to provide a realistic virtual platform. To offer flexibility in the control design process, experimental data for identification purposes, finite element models for the reference structure, numerical, and physical substructure, and plant models with model uncertainties are provided. Also, a sample example of an RTHS design based on a linear quadratic Gaussian controller is included as part of a computational code package, which facilitates the exploration of the tradeoff between robustness and performance of tracking control designs. The goals of this benchmark are to: extend existing control or develop new control techniques; provide a computational tool for investigation of the challenging aspects of maRTHS; encourage a transition to multiple actuator RTHS scenarios; and make available a challenging problem for new researchers to investigate maRTHS approaches. We believe that this benchmark problem will encourage the advancing of the next generation of controllers for more realistic RTHS methods.
Keywords: RTHS, maRTHS, MIMO control, estimation, uncertainty, coupling, hydraulic actuator, transfer system
Authors: Amr S. Elnashai; Billie F. Spencer; Dan A. Kuchma; Guangqiang Yang; Juan Carrion; Quan Gan; and Sung Jig Kim
DOI: 10.1007/1-4020-4571-9_16
Abstract: The Multi-Axial Full-Scale Sub-Structured Testing and Simulation facility (MUST-SIM) is a state-of-the-art physical and analytical simulation environment capable of representing the inelastic seismic response of full-scale structure-foundation-soil systems. Three Load and Boundary Condition Boxes (LBCBs) provide full hybrid action-deformation control at each of their three contact points. An L-shaped prestressed concrete wall provides the reaction structure for testing of full-scale sub-structures while a suite of advanced analysis software is available for analytical simulation. The paper describes four sets of simulations under investigation. These are an RC bridge and a steel building, at scales between 1:1 and 1:16. Early results using a new concept of integrated simulation combining analytical and experimental components are reported on complex structure-foundation-soil bridge systems.
Keywords: RTHS, maRTHS, MIMO control, estimation, uncertainty, coupling, hydraulic actuator, transfer system
Authors: Guoxi Fan; Yupu Song; and Licheng Wang
DOI: 10.1177/0731684413512706
Abstract: The reinforced concrete beam-column joint exhibits different properties under dynamic loading when compared with that under quasi-static loading, due to the effect of strain rate. However, the majority of previous studies are focused more on the rate effect of concrete and reinforcement, but less on beam-column joints. Based on the former considerations, the seismic behavior of 15 cruciform specimens subjected to various strain rates is studied in this paper, aimed at attaining a better understanding of the effect of strain rates on beam-column joints. In terms of the effect of different strain rates, the failure mode, carrying capacity, stiffness degradation, and energy dissipation of beam-column joints are discussed in detail. An empirical equation to predict the dynamic increase factor of horizontal shear carrying capacity of beam-column joints under different axial compression ratios and strain rates is also proposed through multiple linear regression analysis. Finally, four adjustments for the softened strut-and-tie model are made to get better predicting of the test results. It has been proved that predicted results by the improved softened strut-and-tie model are in good agreement with the test results.
Keywords: RTHS, maRTHS, MIMO control, estimation, uncertainty, coupling, hydraulic actuator, transfer system
Authors: Hosam K. Fathy; Zoran S. Filipi; Jonathan Hagena; and Jeffrey L. Stein
DOI: 10.1117/12.667794
Abstract: Hardware-in-the-loop (HIL) simulation is rapidly evolving from a control prototyping tool to a system modeling, simulation, and synthesis paradigm synergistically combining many advantages of both physical and virtual prototyping. This paper provides a brief overview of the key enablers and numerous applications of HIL simulation, focusing on its metamorphosis from a control validation tool into a system development paradigm. It then describes a state-of-the art engine-in-the-loop (EIL) simulation facility that highlights the use of HIL simulation for the system-level experimental evaluation of powertrain interactions and development of strategies for clean and efficient propulsion. The facility comprises a real diesel engine coupled to accurate real-time driver, driveline, and vehicle models through a highly responsive dynamometer. This enables the verification of both performance and fuel economy predictions of different conventional and hybrid powertrains. Furthermore, the facility can both replicate the highly dynamic interactions occurring within a real powertrain and measure their influence on transient emissions and visual signature through state-of-the-art instruments. The viability of this facility for integrated powertrain system development is demonstrated through a case study exploring the development of advanced High Mobility Multipurpose Wheeled Vehicle (HMMWV) powertrains.
Keywords: Hardware-In-The-Loop, Engine-In-The-Loop, Dynamometer, Hybrid Powertrains, High Mobility Multipurpose Wheeled Vehicle
Authors: Douglas A. Foutch; Subhash C. Goel; and Charles W. Roeder
DOI: http://hdl.handle.net/2142/14140
Abstract: A full-scale six-story steel building was constructed and tested as part of the U.S./Japan Cooperative Earthquake Research Program Utilizing Large Size Testing Facilities. The program was jointly funded by the Ministry of Construction of Japan and the United States National Science Foundation. The overall objective of the program is to improve seismic safety in practice and to determine the relationships among full-scale tests, small-scale tests, component tests and analytical studies. The full-scale building was 15m square in plan and measured 22.38m from the test floor to the top of the roof girders. It was tested as a concentric braced frame; repaired and tested as an eccentric braced frame; tested as a moment frame; and finally, tested with cladding and other nonstructural elements installed. The tests were conducted using the pseudodynamic testing technique which simulated actual seismic loadings. This preliminary report describes the full-scale building and the testing program and presents preliminary results and conclusions.
Keywords: Earthquake Motions, Earthquake Engineering, Elasticity
Authors: Thomas Frankie; Adel Abdelnaby; Pedro Silva; David Sanders; Amr Elnashai; Billie Spencer; Daniel Kuchma; and Chai Ming Chang
DOI: 10.1061/9780784412848.064
Abstract: Curved bridges are subject to combined loading conditions resulting from complex earthquake ground motions coupled with irregular geometry and asymmetry of the bridge structure. This paper describes a part of the CABER project that compares the experimental results of a curved bridge under multidirectional earthquake loading with its un-calibrated numerical predictions. The numerical predictions are obtained from an analytical model established using the Zeus-NL analysis platform. The experimental results are obtained from a hybrid experimental/analytical test performed at the NEES MUST-SIM Facility at the University of Illinois at Urbana-Champaign. In the hybrid test, the bridge is substructured into three analytical (one) and experimental (two) modules. Disagreements shown between the experimental and numerical results highly indicate the inadequacy of the existing analytical solutions. Numerical model assumptions and inaccuracy are identified and methods of numerical model calibration are proposed. © 2013 American Society of Civil Engineers.
Keywords: Civil and Structural Engineering; Building and Construction
Authors: Bora Gencturk and Farshid Hosseini
DOI: 10.1139/cjce-2013-0445
Abstract: Curved bridges are subject to combined loading conditions resulting from complex earthquake ground motions coupled with irregular geometry and asymmetry of the bridge structure. This paper describes a part of the CABER project that compares the experimental results of a curved bridge under multidirectional earthquake loading with its un-calibrated numerical predictions. The numerical predictions are obtained from an analytical model established using the Zeus-NL analysis platform. The experimental results are obtained from a hybrid experimental/analytical test performed at the NEES MUST-SIM Facility at the University of Illinois at Urbana-Champaign. In the hybrid test, the bridge is substructured into three analytical (one) and experimental (two) modules. Disagreements shown between the experimental and numerical results highly indicate the inadequacy of the existing analytical solutions. Numerical model assumptions and inaccuracy are identified and methods of numerical model calibration are proposed. © 2013 American Society of Civil Engineers.
Keywords: Small-Scale Testing, Reinforced Concrete, Engineered Cementitious Composites, Hybrid Simulation
Authors: W. Ghannoum; V. Saouma; G. Haussmann; K. Polkinghorne; M. Eck; and Dae-Hung Kang
DOI: 10.1061/9780784412848.064
Abstract: Seismic loading rates can significantly affect the behavior of reinforced concrete (RC) elements. However, few data are available to quantify these effects. Shaking table tests allow the study of loading rate phenomena; however, they suffer from difficulties in assessing causality (direct assessment of causes on effects) and are expensive to conduct. An alternative is to test individual RC elements by directly imparting high-velocity loading protocols. However, multiactuator setups are necessary to achieve seismically representative loading and boundary conditions, which entails particularly challenging control requirements. This investigation makes use of recent advances in real-time testing hardware to study the effects of loading rates on the structural response of lightly confined RC columns. A pioneering test setup in which three actuators are controlled independently at high velocities was used to test a series of columns until axial collapse. The experimental challenges and column behavior are discussed.
Keywords: Loading Rates, Reinforced Concrete, Concrete Columns, Shear Failure, Axial Collapse
Authors:N. Harris McClamroch
DOI: https://www.iitk.ac.in/nicee/wcee/article/8_vol6_127.pdf
Abstract: The pseudo dynamic test method provides a means for static testing full scale structures subjected to simulated earthquake ground motions. The method uses an online computer to calculate the appropriate inertia forces which are experimentally applied to the structure. Experimental and theoretical research has been continuing in the United States and Japan to apply this method to buildings subjected to damaging level earthquakes. This paper summarizes studies on the characteristics of the actuator controller and the need for careful implementation of the method.
Keywords: Pseudo Dynamic Test, Earthquake Ground Motions, Actuator Controller
Authors: Sadraddin, H.L.; Cinar, M.; Shao, X.; and Ahmed, M.
DOI: 10.1007/s40799-020-00390-9
Abstract:Real-time hybrid simulation (RTHS) plays an essential role in understanding the time-dependent behavior of structures when subject to extreme hazard loadings in civil engineering research. During RTHS, physical experiment on critical substructure component(s) and numerical simulation of the remaining structure are seamlessly integrated to obtain the whole structural response at the system level. To leverage testing equipment among several laboratories for complex structure systems, distributed real-time hybrid simulation (dRTHS) was proposed and has been successfully applied in seismic experimentation of building structures. In addition to actuator delay experienced in a typical RTHS experiment, network delay due to data transmission between controllers of loading equipment located at geographically distributed laboratories also exists in dRTHS. To compensate the total large and varying time delay, four delay compensation methods were implemented in a recently developed dRTHS testing platform and their performances were evaluated through a series of virtual and physcial dRTHS experiments. The development of the dRTHS testing platform and the four delay compensation methods are introduced first. Then testing results demonstrating the effectivness of these methods are presented together with the reliability of dRTHS experimental method in earthquake engineering and its potential applicability in other engineering fields.
Keywords: Structural seismic response, Time-dependent behavior, Distributed real-time hybrid testing, Time delay, Delay compensation
Authors:Ning, X.; Wang, Z.; Wang, C.; and Wu, B.
DOI: 10.1080/13632469.2020.1823912
Abstract:This study proposed a general framework for adaptive delay compensation in real-time hybrid simulation(RTHS). This framework is composed of two main parts: an adaptive feedforward controller to handle variable time delay and amplitude discrepancies, and a feedback controller to enhance the robustness of compensation. In particular, the adaptive feedforward controller is determined using a discrete physical testing system (PTS) model, whose parameters are estimated using the least-squares method. Moreover, the feedback controller is introduced to reduce dependency on the PTS model of the feedforward controller. Results of virtual and actual RTHS alongside five other compensation strategies revealed the superiority of the proposed compensation method.
Keywords: Real-time hybrid simulation,delay compensation,adaptive feedforward,control,feedback control
Authors:Bas, E.E. and Moustafa, M.A.
DOI: 10.3390/make2040026
Abstract:Hybrid simulation (HS) is an advanced simulation method that couples experimental testing and analytical modeling to better understand structural systems and individual components’ behavior under extreme events such as earthquakes. Conducting HS and real-time HS (RTHS) can be challenging with complex analytical substructures due to the nature of direct integration algorithms when the finite element method is employed. Thus, alternative methods such as machine learning (ML) models could help tackle these difficulties. This study aims to investigate the quality of the RTHS tests when a deep learning algorithm is used as a metamodel to represent the dynamic behavior of a nonlinear analytical substructure. The compact HS laboratory at the University of Nevada, Reno was utilized to conduct exclusive RTHS tests. Simulating a braced frame structure, the RTHS tests combined, for the first time, linear brace model specimens (physical substructure) along with nonlinear ML models for the frame (analytical substructure). Deep long short-term memory (Deep-LSTM) networks were employed and trained to develop the metamodels of the analytical substructure using the Python environment. The training dataset was obtained from pure analytical finite element simulations for the complete structure under earthquake excitation. The RTHS evaluations were first conducted for virtual RTHS tests, where substructuring was sought between the LSTM metamodel and virtual experimental substructure. To validate the proposed RTHS testing methodology and full system, several actual RTHS tests were conducted. The results from ML-based RTHS were evaluated for different ML models and compared against results from conventional RTHS with finite element models. The paper demonstrates the potential of conducting successful experimental RTHS using Deep-LSTM models, which could open the door for unparalleled new opportunities in structural systems design and assessment.
Keywords: Real-time hybrid simulation,delay compensation,adaptive feedforward,control,feedback control
Authors: Guo, W.; Wang, Y.; Zeng, C.; Wang, T.; Gu, Q.; Zhou, H.; Zhou, L.; and Hou, W.
DOI: 10.1080/13632469.2021.1999869
Abstract: This study aimed to provide an experimental evaluation method for train’s moving safety on a post-earthquake bridge. First, an improved real-time hybrid simulation (RTHS) framework was constructed, based on utilizing the moving load superposition algorithm to solve the train-track-bridge interaction (TTBI) problem. An RTHS test was then conducted for the TTBI problem. The train model was tested using a shake table and was dynamically linked to the numerical substructure. A post-earthquake seven-span high-speed railway simply supported bridge was studied, in which earthquake-induced damage, such as stiffness reductions, residual displacements of piers, girder gap expansions, and pier settlements were all tested.
Keywords: Moving safety evaluation,real-time hybrid simulation,moving load superposition algorithm,high-speed railway bridge,earthquake-induced damage,pier settlement
Authors:Liqiao, L.; Jinting,W.; Hao, D.; and Fei, Z.
DOI: 10.1007/s11803-021-2073-0
Abstract: This paper aims to investigate the critical stability of a multi-degree-of-freedom (multi-DOF) real-time hybrid simulation (RTHS). First, the critical time-delay analysis models are developed using the continuous- and discrete-time root locus (RL) techniques, respectively. A bilinear transform is introduced into the first-order Padé approximation while conducting the discrete RL analysis. Based on this technique, the time delay can be explicitly used as the gain factor and thus the instability mechanism of the multi-DOF RTHS system can be analyzed. Subsequently, the critical time delays calculated by the continuous- and discrete-time RL techniques, respectively, are compared for a 2-DOF RTHS system. It is shown that assuming the RTHS system to be a continuous-time system will result in overestimating the critical time delay. Finally, theoretically calculated critical delays are demonstrated and validated by numerical simulation and a set of RTHS experiments. Parametric analysis provides a glimpse of the effects of time step, frequency and damping ratio in a performing partitioning scheme. The constructed analysis model proves to be useful for evaluating the critical time delay to predict stability and performance, therefore facilitating successful RTHS.
Keywords: real-time hybrid simulation, root locus, critical time delay, delay-dependent stability
Authors:Gálmez, C. and Fermandois, G.
DOI: 10.1002/stc.2962
Abstract: This study presents a robust adaptive model-based compensation framework for real-time hybrid simulation (RTHS), capable of minimizing synchronization errors with uncertain experimental substructures. The initial conditions of the compensator are defined using a nominal model of the transfer system without consideration of specimen–actuator interaction. Then, robust calibration of the compensator is obtained through offline numerical simulations using particle swarm optimization. The proposed methodology is validated in a virtual RTHS benchmark problem but incorporates more complex scenarios such as uncertain and nonlinear experimental substructures for the same compensator design. The results show excellent accuracy and robustness of the proposed methodology, with quick adaptation for different substructuring scenarios. Furthermore, this methodology proves that a robust compensator designed independently from the experimental substructure can be helpful to avoid tedious calibration and early tests of the physical specimen, with unintentional premature damage effects.
Keywords: adaptive compensation, benchmark problem, real-time hybrid simulation, robustness,optimization
Authors:Huang, W.; Ning, X.; Ding, Y.; and Wang, Z.
DOI: 10.1142/S0219455423501079
Abstract: To address the varying time-delay problem in real-time hybrid simulation (RTHS), an unscented Kalman filter (UKF)-based adaptive time-delay compensator (UKF-ADC) is proposed in this study. UKF-ADC comprises of two main parts: a feedforward controller with adjustable parameters and a parameter estimator of UKF. The former is constructed with the inverse model of the control plant, which is represented by a first-order transfer function, whereas the latter is used to estimate and update the parameters online in the feedforward controller using displacement commands and measurements. To fully explore the performance of UKF-ADC, the effects of the initial parameters in UKF and factor α in the compensator are investigated through a prescribed displacement command adopting a nonlinear actuator model. As a result, the performance of UKF-ADC is mainly affected by factor α and robust to the initial parameters of UKF. In addition, a series of virtual and actual RHTSs are performed, employing the validated compensator. The results reveal that UKF-ADC can effectively improve the accuracy of RTHS and exhibit strong robustness.
Keywords: Real-time hybrid simulation, adaptive delay compensation, parameter estimation, unscented Kalman filter
Authors:Chen, M.; Gao, X.; Chen, C.; Guo, T.; and Xu, W.
DOI: 10.1080/13632469.2022.2134945
Abstract: This study proposes the use of nonlinear autoregressive with exogenous input (NARX) to emulate dynamic behavior of analytical substructures in real-time hybrid simulation (RTHS). The training of the NARX model can be conducted numerically, and its implementation presents a good representation of structural dynamics with minimum computational demands on the RTHS equipment. A Kriging metamodel is further introduced to surrogate the NARX model coefficients to account for ground motion uncertainties. RTHS of a single-degree-of-freedom (SDOF) structure with a self-centering viscous damper are conducted as proof of concept to experimentally demonstrate the effectiveness of proposed Kriging-NARX metamodeling approach.
Keywords: Real-time hybrid simulation,uncertainty,nonlinear, Kriging,surrogate model,structural dynamics
Authors:Palacio-Betancur, A. and Gutierrez Soto, M.
DOI: justdoi
Abstract: Predicting complex structures’ dynamic behavior is challenging, especially since full-scale testing of structures subjected to natural hazards is not always possible. Testing individual systems is insufficient, and consequently, engineering experimentation requires refinement. Hybrid simulation (HS) is a cost-effective and efficient dynamic testing technique that evaluates a systems’ performance with rate-dependent behavior. HS is also known as cyber-physical testing, dynamic virtualization, pseudo-dynamic testing, dynamic sub-structuring, and hardware-in-the-loop. In structural engineering, it consists of combining experimental-analytic simulations of structures subjected to dynamic loading. It seeks to: (1) leverage established understandings about the physical world to gain insight into the behavior of physical systems that have limited prior knowledge, and (2) study the coupling of physical and computational models to realistically include their dynamic interactions. The cyber-physical setup consists of dividing a structure into numerical and physical substructures and using actuators to achieve the coupling. The actuator dynamics generate a time delay in the overall system that affects the simulation’s accuracy and stability. Hence, tracking control methodologies strive to mitigate these adverse effects. Cyber-physical testing with linear, pre-determined models has been studied and established. Thus, recent studies seek to enable the most realistic conditions for such engineering experimentation through robust, nonlinear and adaptive control methodologies to address challenging cases involving damage, failures, or sharply changing dynamics. This paper presents a state-of-the-art review of recent tracking control methodologies for real-time hybrid simulation (RTHS), including identifying the limitations and challenges of modern implementations. Furthermore, this paper presents a comparative study evaluating control methodologies using a benchmark problem.
Keywords: real-time hybrid simulation, literature review
Authors:Sun, C.; Song, W. and Jahangiri, V.
DOI: 10.1016/j.oceaneng.2022.112529
Abstract: Offshore wind farms are experiencing rapid growth globally where floating offshore wind turbines (FOWTs) have been attracting increasing research and industry investment. To achieve secure application, it is essential to develop numerical models and conduct laboratory testing to develop an in-depth understanding of the complex structural behavior of FOWTs under combined wind-wave loading. However, model testing of FOWTs is complicated by the Reynolds-Froude scaling incompatibilities. This research proposes a real-time hybrid simulation (RTHS) framework to study the structural performance of FOWTs under wind-wave loading. In the framework, the blades (nacelle) and tower are numerically modeled, and the floating platform is tested in real-time via an actuation system in a laboratory. The numerical and physical substructures communicate at the tower-floater interface. The National Renewable Energy Lab 5 MW spar-type FOWT on a scale of 1:50 is simulated to evaluate the feasibility of the proposed framework. Errors caused by delays and noises are quantified through sensitivity analyses. Results show that the delays in the sensors and actuators influence the performance of the RTHS framework more significantly than the noises. Overall, the response relative errors in the RTHS framework are small and tolerable under delays, noises, and representative wind-wave conditions. The proposed framework and sensitivity analyses presented in this study provide important information for future implementation and further development of the RTHS technology for similar marine structures.
Keywords: Real-Time Hybrid Simulation, Real-Time Hybrid Simulation, Wind-Wave Loading
Authors: Chen, C.; Yang, Y.; Hou, H.; Peng, C.; and Xu, W.
DOI: 10.1002/eqe.3690
Abstract: Real-time hybrid simulation (RTHS) provides an effective and efficient experimental technique to enable large- or full-scale experiments to account for rate-dependent behavior in size limited laboratories. Traditional practice of RTHS assumes deterministic substructure properties therefore could not account for structural uncertainties in global response prediction. This study explores the use of Co-Kriging metamodeling for global response prediction under the presence of structural uncertainties. RTHS in laboratory is used as high-fidelity (HF) modeling while computational simulation of the prototype structure under investigation is used as low-fidelity (LF) modeling. Multifidelity modeling is integrated through Co-Kriging to render accurate response prediction over the entire sample space of structural uncertainties. An entropy-based adaptive strategy is used to sequentially determine the sampling points for HF RTHS and LF simulation. The proposed multifidelity Co-Kriging approach is experimentally evaluated through RTHS of a single-degree-of-freedom structure with a self-centering viscous damper. The Co-Kriging predicted maximum structural responses are further compared with validation tests. It is demonstrated that the Co-Kriging can effectively reduce the number of RTHS tests in laboratory and significantly improve the metamodel accuracy for global prediction of structural response under uncertainties. The presented study presents an innovative way to further expand the capacity of RTHS for uncertainty quantification toward seismic hazard mitigation.
Keywords: Real-Time Hybrid Simulation, Co-Kriging Metamodeling, Structural Uncertainties, Global Response Prediction
Authors: Liu, Y. H.; Lai, Z. F.; Mercan, O.; Tan, P.; and Zhou, F. L.
DOI: 10.1142/S0219455424500913
Abstract: Real-time hybrid simulation (RTHS) is an economical and reliable method for the evaluation of structural dynamic performances, and the fixed analytical substructure model is often used in RTHS which may affect the accuracy of results. In this study, a real-time hybrid simulation platform (RTHSP) developed by configuring a generic National Instruments (NI) controller with hybrid programming strategy is presented in detail. The dynamic performances of a scaled base isolated structure, where the unscented Kalman filter (UKF) was used to update the analytical substructure Bouc–Wen model during the RTHSs was evaluated by presented RTHSP. RTHS of a base-isolated structure was performed where a lead rubber bearing (LRB) was tested physically as the experimental substructure of a part of the isolation layer and the superstructure with the rest of the isolation layer model updated by UKF was considered as the analytical substructure. Under the excitation of three natural earthquakes, the RTHSs with and without UKF updating were compared and analyzed the differences between the two. The results indicated that the displacements of experimental substructure generated by RTHS with UKF updating are the largest, while the relative displacements and acceleration of superstructure are the smallest overall, and the dynamic characteristics of the isolation layer of the analysis substructure updated by UKF are different from that without updated, which reflected the more authentic dynamic mechanical performance of the base-isolated structure under earthquake excitation. In addition, the RTHSP and the hybrid programming strategy are verified to be reliable in tests and experiments, and the components and implementation of a RTHSP for base-isolated structures is described in detail, providing a reference for research on RTHS method.
Keywords: Real-Time Hybrid Simulation, Base-Isolated Structure, Unscented Kalman Filter, Structural Dynamic Performances
Authors: Ning, X.; Huang, W.; Xu, G.; Wang, Z.; Wu, B.; Zheng, L.; and Xu, B.
DOI: 10.1155/2023/5550580
Abstract: Adaptive control methods have been widely adopted to handle the variable time delay in real-time hybrid simulation (RTHS). Nevertheless, the initial parameter settings in adaptive control law, the parameter estimation method, and the testing system nonlinearity will affect RTHS’s accuracy and stability at different levels. To this end, this study proposes a novel model-based adaptive feedforward-feedback control method that considers an additive error model. In the proposed method, the time delay and amplitude discrepancy are roughly compensated by a feedforward controller and then finely reduced by an adaptive controller, and an outer-loop control formed by the feedback controller is introduced to improve the ability and robustness furthermore. What’s more, the testing system, composed of the transfer system and physical specimen, is divided into the nominal and additive error models. The feedforward controller is devised using the inverse nominal model, whose parameters are constant. The adaptive controller is designed to adopt a discrete-time additive error model, in which the parameters are identified online by the Kalman filter. Numerical simulations, parametric studies, and actual experiments were carried out to inspect the feasibility and effectiveness of this method thoroughly. Results indicate that the proposed method can effectively improve the accuracy and stability of RTHS and significantly reduce the dependence on the adaptive control law. Moreover, the proposed method exhibits strong robustness and is, therefore, useful in RTHS.
Keywords: Adaptive Control, Real-Time Hybrid Simulation, Feedforward-Feedback Control, Kalman Filter
Authors: Park, J.; Park, M.; Chae, Y.; and Kim, Y.
DOI: 10.1080/13632469.2023.2197501
Abstract: The vertical component of ground motions can affect the seismic performance of reinforced concrete (RC) piers as significant as its horizontal counterpart. However, real-time testing for RC piers subjected to both horizontal and vertical ground motions has been scarcely conducted due to the difficulty in multi-axial control of actuators. In this study, the seismic response of a bridge RC pier was investigated by conducting real-time hybrid simulation (RTHS), where the RC pier was physically tested in the laboratory and the bridge superstructure was numerically modeled. The test setup that can synchronously apply both horizontal and vertical ground motions was constructed by using three dynamic actuators and a flexible loading beam (FLB). The lateral response of the RC pier was investigated by varying the intensities for vertical ground motions, while the same intensity for horizontal ground motion is used. It was found that the axial force from the dead load of superstructure can significantly affect the initial stiffness, strength, and post-yield response of the RC pier. For the selected earthquake ground motions, however, the intensity of vertical ground motion did not make a substantial difference in the lateral response, although there was a notable difference in the fracture pattern.
Keywords: Seismic Performance, Reinforced Concrete Piers, Real-Time Hybrid Simulation, Vertical Ground Motions
Authors: Huang, X.; Park, J.; and Kwon, O.-S.
DOI: 10.1080/13632469.2023.2197501
Abstract: A network interface program for controllers (NICON) for pseudo-dynamic hybrid simulations is presented. The program is implemented as an independent program residing between the simulation model and an actuator controller with various functions necessary for hybrid simulations, such as communication, coordinate transformation, error compensation. These functions are generalized to allow for a generic configuration of actuator setup theoretically with any number of control points and control degrees of freedom. Application examples of NICON to hybrid simulations of civil infrastructures subjected to earthquakes or fire are presented.
Keywords: Network Interface Program, Pseudo-Dynamic Hybrid Simulations, Actuator Control, Error Compensation
Authors: Sepulveda, C.; Mosqueda, G.; Wang, K.; Huang, P.; Huang, C.; Uang, C.; and Chou, C.
DOI: 10.1002/eqe.4048
Abstract: A novel framework for hybrid simulation of the seismic response of structures is presented that employs a mixed displacement and force control strategy. A key feature of this framework is a controller-based displacement-to-force transformation that enables compatible displacements between the numerical and experimental model for force-controlled degrees of freedom. The framework can be applied within conventional displacement-based time-integration algorithms allowing for implementation across a variety of software and hardware architectures; it is demonstrated here using OpenSees software with detailed nonlinear numerical models. This study includes numerical verification of the proposed force control strategy and actual implementation in a hybrid simulation of special moment frames with full-scale beam-column subassemblies. In the hybrid tests, the experimental column axial load is applied in force control due to the large stiffness and when combined with lateral seismic loads, results in column local buckling with significant axial shortening. The hybrid simulation results verify that the proposed mixed displacement and force control strategy effectively enforces displacement compatibility and force equilibrium between the numerical and experimental structures at the boundary degrees of freedom.
Keywords: Hybrid Simulation, Seismic Response, Force Control Strategy, Displacement Compatibility
Authors: Zeng, C.; Guo, W.; and Shao, P.
DOI: 10.1177/10775463231167251
Abstract: The accuracy of real-time hybrid simulation (RTHS) is greatly influenced by the inevitable time delay and amplitude error due to the control plant dynamics. Several tracking controllers have been implemented to improve the overall performance, and among them, model predictive control (MPC) loses its prediction advantage due to the characteristic of real-time command calculation of RTHS. In this study, an improved tracking controller based on MPC controller combined with a polynomial-based forward reference prediction (MPC-RP) is proposed according to the principle of providing future data insight. First, the proposed controller is described, and the basic implementation procedure is presented. Then, validation tests were carried out to evaluate the tracking performance of the proposed controller based on the virtual RTHS benchmark problem. The results show that the MPC-RP controller has an effective delay compensation performance and a good amplitude error regulation capacity. It is also demonstrated that the MPC-RP controller has a great robust performance concerning control plant uncertainties, which ensures highly improved accuracy of RTHS.
Keywords: Real-Time Hybrid Simulation, Tracking Controller, Model Predictive Control, Delay Compensation
Authors: Xu, W., Meng, X., Chen, C., Guo, T., & Peng, C.
DOI: 10.3389/fbuil.2024.1374819
Abstract: Actuator control takes a pivotal role in achieving stability and accuracy, particularly in the context of multi-axial real-time hybrid simulation (maRTHS). In maRTHS, multiple hydraulic actuators are necessitated to apply precise motions to experimental substructures thus necessitating the application of multiple-input multiple-output (MIMO)control strategies. This study evaluates the data-driven nonlinear autoregressive with external input (NARX) based compensation for the servo-hydraulic dynamics within the maRTHS benchmark model. Different from previous study, nonlinear terms are incorporated into the NARX model. Online least square and ridge regression techniques are utilized to estimate the model coefficients to achieve optimal compensation. The influence of various model order and window length is assessed for the NARX model-based compensation. The findings of this research demonstrate that NARX-based compensation has significant potential not only in facilitating precise actuator control for maRTHS but also in enabling robust control in the presence of unknown uncertainties inherent to the servo-hydraulic system.
Keywords: Actuator Control, Multi-Axial Real-Time Hybrid Simulation, NARX Compensation, MIMO Control Strategies
Authors: Cho, C. B.; Chae, Y.; and Park, M.
DOI: 10.1002/eqe.4024
Abstract: One of the challenges in real-time dynamic testing is effectively controlling axial forces for axially stiff members such as columns, walls, and base isolators. Axial force has a significant influence on structural strength and post-yield behavior, thereby maintaining proper axial force boundary conditions is crucial for accurate seismic performance evaluation. To overcome this challenge, a displacement-based force control method using the adaptive time series compensator (D-ATS) was developed in the existing study, but this method requires additional sensors such as displacement transducers and accelerometers to ensure the accuracy of force control. In this study, a new real-time force control method is introduced, which eliminates the need for additional sensors beyond the default sensors available in a typical servo-hydraulic actuator. Newly developed modules are also provided, which can satisfactorily estimate the velocity and force change rate of actuator, while effectively mitigating oil-column resonance. Experimental validation is conducted using lead rubber bearings (LRBs) subjected to axial force and lateral movements. The results demonstrate the exceptional performance of the new force control method, offering a convenient and cost-effective approach for applying axial forces in real-time dynamic testing.
Keywords: Real-Time Dynamic Testing, Axial Force Control, Adaptive Time Series Compensator, Servo-Hydraulic Actuator
Authors: Dong, J.; Wojtkiewicz, S.F.; Lobo-Aguilar, S.; Yuan, Y.; and Christenson, R.E.
DOI: 10.1061/JENMDT.EMENG-7158
Abstract: An innovative experimental method, called aeroelastic real-time hybrid simulation (aeroRTHS), is proposed to study the aerodynamic vibrations of a building model in a boundary layer wind tunnel (BLWT). The aeroRTHS method aims to capture the dynamic interactions between an aeroelastic structure and the applied wind load to accurately characterize complicated, unstable phenomena such as vortex-induced vibration, and in doing so, to broaden the application of real-time hybrid simulation (RTHS) from seismic applications to wind engineering. The aeroRTHS tests were conducted in the BLWT at the University of Florida Natural Hazards Engineering Research Infrastructure Equipment Facility (UF NHERI EF). A 1-m-tall rigid physical model with an aspect ratio (height/width) of 7.3 was mounted on a modified single-axis shake table converting translational motions to corresponding rotations at the base of the model allowing the model to behave in the wind tunnel as an aeroelastic structure. A total of 128 pressure sensors located on the cross-wind sides of the physical building model measured wind pressures which then were converted to equivalent forces and ultimately resolved into a single equivalent force at the top of the physical building model based on the moment equilibrium at its base. The results from a series of aeroRTHS tests in the BLWT are reported herein to constitute a proof-of-concept study that validates the aeroRTHS method and demonstrates the aeroelastic effects on a flexible and slender structure.
Keywords: Aeroelastic Real-Time Hybrid Simulation, Boundary Layer Wind Tunnel, Aerodynamic Vibrations, Vortex-Induced Vibration
Authors: Montoya, H.; Salmeron, M.; Silva, C.E.; and Dyke, S.J.
DOI: 10.1061/JENMDT.EMENG-7637
Abstract: Thermomechanical cyber–physical testing enables two-way thermal coupling between a numerical and an experimental subsystem. The interactions between the numerical model and the physical specimen occur through transfer systems, which enforce interface conditions. Thus, efficient control methodologies are necessary to achieve the desired interface interaction through thermal actuators with minimal error. This study introduces a novel thermal transfer system that imposes distributed cooling (or heating) thermal loads on a physical subsystem. First, the thermal actuator is identified considering switching-mode continuous dynamics for heating and cooling conditions. A switching-mode estimation algorithm is adopted to estimate the operating thermal cycle of the actuator in real-time. A control system is developed to experimentally impose the desired temperature and reduce tracking error (i.e., the error between the desired and actual temperature) under different thermal cycles. The identification and control of the thermal transfer system are then validated through a set of experiments considering different temperature rates of change. The developed control system is found to effectively minimize tracking errors in real-time cyber–physical experiments.
Keywords: Thermomechanical, Thermal Actuator, Switching Control
Authors: Dong, J.; Wojtkiewicz, S.F.; and Christenson, R.E.
DOI: 10.1061/JENMDT.EMENG-7159
Abstract: High-rise structures with large aspect ratios are subjected to unexpected motions under wind excitation. Structural vibrations induced by vortices in the wake were captured by aeroelastic real-time hybrid simulation (aeroRTHS) in the companion paper. An effective and practical method is critical for explaining the mitigation of adverse wind loading impact upon these structures. Analyzing the performance of structural control devices against wind excitation in an aeroelastic wind tunnel test often is time- and cost-intensive. In this paper, aeroRTHS testing is extended to include (1) a vibration control device numerically added to the numerical substructures and tested to mitigate the cross-wind oscillation in the aeroRTHS framework; and (2) the use of 128 pressure sensors installed on two side faces of a physical building model in a boundary layer wind tunnel (BLWT) at the University of Florida Natural Hazards Engineering Research Infrastructure Equipment Facility (UF NHERI EF) to provide a more complete description of the wind-force distributions imparted on nine building configurations both with and without a tuned mass damper (TMD) at various constant wind speeds. Wind-force distribution was characterized in the time domain in terms of time histories of equivalent forces and displacements, and envelopes of wind forces. Frequency response analysis was conducted based on power spectral densities of input equivalent wind forces and output structural dynamic response. Results from the aeroRTHS tests demonstrated that the aeroRTHS method is capable of investigating aeroelastic structures with passive mitigation devices. The aeroRTHS tests in the wind tunnel demonstrated that the augmentation of buildings with TMDs is an effective way to attenuate the cross-wind vibration in tall buildings.
Keywords: Aeroelastic Real-Time Hybrid Simulation, Wind Excitation, Structural Control Devices, Tuned Mass Damper
Authors: Quiroz, M., Gálmez, C. and Fermandois, G.A.
DOI: 10.3389/fbuil.2024.1394952
Abstract: Real-time hybrid simulation (RTHS) is a powerful and highly reliable technique integrating experimental testing with numerical modeling for studying rate-dependent components under realistic conditions. One of its key advantages is its cost-effectiveness compared to large-scale shake table testing, which is attained by selectively conducting experimental testing on critical parts of the analyzed structure, thus avoiding the assembly of the entire system. One of the fundamental advancements in RTHS methods is the development of multi-dimensional dynamic testing. In particular, multi-axial RTHS (maRTHS) aims to prescribe multi-degree-of-freedom (MDOF) loading from the numerical substructure over the test specimen. Under these conditions, synchronization is a significant challenge in multiple actuator loading assemblies. This study proposes a robust and decentralized adaptive compensation (RoDeAC) method for the next-generation maRTHS benchmark problem. An initial calibration of the dynamic compensator is carried out through offline numerical simulations. Subsequently, the compensator parameters are updated in real-time during the test using a recursive least squares adaptive algorithm. The results demonstrate outstanding performance in experiment synchronization, even in uncertain conditions, due to the variability of reference structures, seismic loading, and multi-actuator properties. Notably, this achievement is accomplished without needing detailed information about the test specimen, streamlining the procedure and reducing the risk of specimen deterioration. Additionally, the tracking performance of the tests closely aligns with the reference structure, further affirming the excellence of the outcomes.
Keywords: Real-Time Hybrid Simulation, Multi-Axial RTHS, Adaptive Compensation, Experimental Synchronization
Authors: Waldbjoern, J.P.; Andersen, S.; Hoegh, J.H.; and Berggreen, C.
DOI: justdoi
Abstract: This paper represents a single component multi-rate Real-Time Hybrid Simulation (mrRTHS) strategy for structural assessment of a cantilever Glass Fiber Reinforced Polymer (GFRP) beam loaded at the tip by a sinusoidal point load. This emulated structure is implemented as a simplified wind turbine blade in terms of geometry, scale and load – here with special attention paid to the root and max-chord section. Thus, the experimental substructure comprises the clamped end of the GFRP beam while the free end makes up the numerical substructure. The partitioning between the numerical and experimental substructure – referred to here as the shared boundary – includes a discrete point with 3 degrees-of-freedom (dof). The numerical substructure generates a displacement signal through a Taylor basis with a coarse time step to optimize computational resources. Using the previous displacement data points, a finer control signal is generated to ensure accurate actuator control in the transfer system. A DIC and inertia compensator is implemented to account for the compliance and dynamics imposed by the load train in the transfer system. The structural response is investigated by mrRTHS for an execution frequency in the range: 0.074 Hz – 2.96 Hz for the sinusoidal point load. The system performance is evaluated against an experimental test setup of the emulated structure – referred to here as the experimental reference. With a root-mean-square (RMS) error in the order of 8–20% between the mrRTHS and reference, the system proved successful in terms of stability and overall correlation at the shared boundary, which is considered an important milestone towards single component mrRTHS on a structure like e.g. a wind turbine blade, aircraft wing or similar cantilever-shaped large load carrying structure.
Keywords: Real-Time Hybrid Simulation, Multi-Rate RTHS, GFRP Beam, Structural Assessment
Authors: Su, W. and Song, W.
DOI: 10.1017/aer.2024.46
Abstract: This paper is focused on the stability of real-time hybrid aeroelastic simulation systems for flexible wings. In a hybrid aeroelastic simulation, a coupled aeroelastic system is ‘broken down’ into an aerodynamic simulation subsystem and a structural vibration testing subsystem. The coupling between structural dynamics and aerodynamics is achieved by real-time communication between the two subsystems. Real-time hybrid aeroelastic simulations can address the limitations associated with conventional aeroelastic testing performed within a wind tunnel or with pure computational aeroelastic simulation. However, as the coupling between structural dynamics and aerodynamics is completed through the real-time actuation and sensor measurement, their delays may inherently impact the performance of hybrid simulation system and subsequently alter the measured aeroelastic stability characteristics of the flexible wings. This study aims to quantify the impact of actuation and sensor measurement delays on the measured aeroelastic stability, e.g. the flutter boundary, of flexible wings during real-time hybrid simulations, especially when different aerodynamic models are implemented.
Keywords: Hybrid Aeroelastic Simulation, Flexible Wings, Aeroelastic Stability, Actuation and Sensor Delays
Authors: Huimeng, Z., Xiaoyun, S., Jianwen, Z., Hongcan, Y., Yanhui, L., Ping, T., Yangyang, C., Li, X., Ying, Z., and Wei, G.
DOI: 10.1016/j.tws.2024.111559
Abstract: In May 2021, the 72-story Shenzhen Saige building experienced abnormal vibration that was strongly felt on many floors and triggered social panic. The tower was therefore closed for more than 2 months resulting in huge economic losses. A preliminary study consisting of field resonant excitation tests and a series of numerical simulations were carried out. It was concluded that the wind loads provoked the higher modes of the building vibration. Specifically, the vibration of the mast, which is located at the building top, induced this abnormal vibration. To validate this conclusion, real-time hybrid model (RTHM) tests was developed to reproduce this building vibration incident. This paper presents the details of the validation RTHM tests including testing design and result discussions. Structural vibration parameters obtained from the field tests were used in the numerical substructure building model, and the experimental substructures were the two scaled down mast models (the cantilever beam section of the masts). During RTHM test, the restoring force of the experimental substructure due to real wind loads induced by an air fan was measured and used in the numerical simulation to compute interface motions. A shaking table was then used to impose the interface motion back to the bottom of the mast model to reproduce the abnormal vibration incident. The demonstrated ability of the developed RTHM testing method to reproduce the resonant phenomenon of the wind-induced tower vibration provides an alternative experimental method to study vibration responses of high-rise buildings in future.
Keywords: Real-Time Hybrid Model, Wind-Induced Vibration, High-Rise Building, Resonant Phenomenon
Authors: Sepulveda, C., Cheng, M., Becker, T., Mosqueda, G., Wang, K., Huang, P.. Huang C., Uang, C., and Chou, C.
DOI: 10.1002/eqe.4149
Abstract: This study presents the implementation of an online model updating algorithm within a full-scale hybrid simulation (HS) of a six story, four bay steel moment frame. The experimental substructure consists of a cruciform subassembly generating critical data on the nonlinear behavior of the first story column and two beams with reduced beam sections (RBSs) on each side. The updating algorithm focuses on the modeling parameters of plastic hinge elements representing the RBSs in the numerical model. A smooth plasticity model is utilized for beam plastic hinges with updating parameters identified from on-line experimental data through a modified version of the unscented Kalman filter. The HS shows that the numerical beam hinges based on simple hysteretic model with updated parameters are able to capture the characteristic behavior observed in experiments. Due to fracture of beam flanges is observed in the experiments, a selective updating concept is proposed to allow for updating multiple numerical components accounting for asymmetric behavior and variability in the response. The selective updating method is validated through virtual HSs that are better able to identify and isolate the effects of fracture and other behavioral characteristics. The combination of results from physical and virtual tests highlights the benefits of model updating on the local and overall system-level response.
Keywords: Model Updating, Hybrid Simulation, Steel Moment Frame, Unscented Kalman Filter
Authors: Tian, Y.; Li, Q.; Bu, C.; Fan, F.; and Wang. T.
DOI: 10.3389/fbuil.2024.1424108
Abstract: Multi-axial real-time hybrid simulation (ma-RTHS) utilizes multiple loading devices to realize boundary control with multiple degrees of freedom (MDOF), thus being capable of handling complex dynamic scenarios and multi-dimensional problems. In this paper, a new control technique was developed by using a parallel configuration of double shaking tables to implement shear force and bending moment at the boundary between substructures. The dynamic forces are combined by inertia forces of controlled mass driven by electromagnetic shaking tables. The two shaking tables are packaged as a boundary-coordinating device (BCD). An enhanced three-variable control (ETVC) was proposed to consider the coupling effect between two shaking tables and incorporated with the adaptive time series (ATS) compensator to improve the synchronization of the two shaking tables. The proposed control method was verified by three rounds of hybrid tests on a four-story steel shear frame using different ground motions. Nine criteria were utilized to evaluate the performance of RTHS including both tracking performance and global performance indexes. It was proved that RTHS was successfully implemented, and the boundary forces were well-tracked by the proposed control strategy. Good tracking performance was achieved to prove the effectiveness of the strategy.
Keywords: Multi-Axial Real-Time Hybrid Simulation, MDOF, Boundary Control, Enhanced Three-Variable Control
Authors: Cheng, M.; Ruiz, M.C.; and Becker, T.C.
DOI: 10.1002/eqe.4057
Abstract: Model updating can enhance hybrid simulation by utilizing the experimental data from the physically tested substructure to update the parameters of like-components in the numerical substructure throughout the test, improving the overall accuracy and reducing the extent of the experimental setup. Identifying and updating parameters can be challenging, especially when coupling between degrees of freedom (DOF) must be considered or the specimen experiences loading scenarios which result in newly observed behavior. To explore the performance of model updating under these challenging conditions, a large-scale hybrid simulation was conducted using a model of a major toll bridge with seismic isolation lead rubber bearings (LRB). One LRB is physically tested considering axial, shear, and rotational loading, while the remainder of the bearings are simulated and updated with a phenomenological model within the numerical substructure. A weighted adaptive constrained unscented Kalman filter is applied as the online model updating algorithm. The study explored the effect of learning over different loading patterns, the selection of initial model parameters, and the selection of the physically tested substructure. The improvement of numerical model hysteresis performance accuracy of the force prediction demonstrates the benefits of model updating in large-scale hybrid simulation.
Keywords: Model Updating, Hybrid Simulation, Lead Rubber Bearings, Unscented Kalman Filter
Authors: Aguila, A.J.; Li, H.; Palacio-Betancur, A.; Ahmed, K.A.; Kovalenko, I.; and Gutierrez-Soto, M.
DOI: 10.3389/fbuil.2024.1384235
Abstract: The structural performance of critical infrastructure during extreme events requires testing to understand the complex dynamics. Shake table testing of buildings to evaluate structural integrity is expensive and requires special facilities that can allow for the construction of large-scale test specimens. An attractive alternative is a cyber-physical testing technique known as Real-Time Hybrid Simulation (RTHS), where a large-scale structure is decomposed into physical and numerical substructures. A transfer system creates the interface between physical and numerical substructures. The challenge occurs when using multiple actuators connected with a coupler (i.e., transfer system) to create translation and rotation at the interface. Tracking control strategies aim to reduce time delay errors to create the desired displacements that account for the complex dynamics. This paper proposes two adaptive control methodologies for multi-axial real-time hybrid simulations that improve capabilities for a higher degree of coupling, boundary, complexity, and noise reduction. One control method integrates the feedback proportional derivative integrator (PID) control with a conditional adaptive time series (CATS) compensation and inverse decoupler. The second proposed control method is based on a coupled Model Predictive Control (MPC) with the CATS compensation. The performance of the proposed methods is evaluated using the virtual multi-axial benchmark control problem consisting of a steel frame as the experimental substructure. The transfer system consists of a coupler that connects two hydraulic actuators generating the translation and rotation acting at the joint. Through sensitivity analysis, parameters were tuned for the decoupler components, CATS compensation, and the control design for PID, LQG, and MPC. Comparative results among different control methods are evaluated based on performance criteria, including critical factors such as reduction in the time delay of bothactuators. The research findings in this paper improve the tracking control systems for the multi-axial RTHS of building structures subjected to earthquake loading. It provides insight into the robustness of the proposed tracking control methods in addressing uncertainty and improves the understanding of multiple output controllers that could be used in future cyber-physical testing of civil infrastructure subjected to natural hazards.
Keywords: Real-Time Hybrid Simulation, Multi-Axial Control, Adaptive Control, Tracking Control Strategies
Authors: Al-Subaihawi, S., Ricles, J., Quiel, S., & Marullo, T.
DOI: 10.1016/j.engstruct.2024.118348
Abstract: Real-time hybrid simulation (RTHS) divides a structural system into analytical and experimental substructures that are coupled through their common degrees of freedom. This paper introduces a framework to enable RTHS to be performed on 3D nonlinear models of tall buildings with rate dependent nonlinear response modification devices, where the structure is subjected to multi-directional wind and earthquake natural hazards. A 40-story tall building prototype with damped outriggers is selected as a case study. The analytical substructure for the RTHS consists of a 3-D nonlinear model of the structure, where each member in the building is discretely modeled in conjunction with the use of a super element. The experimental substructure for the RTHS consists of a full-scale rate-dependent nonlinear viscous damper that is physically tested in the lab, with the remaining dampers in the outrigger system modeled analytically. The analytically modeled dampers use a stable explicit non-iterative element with an online model updating algorithm, by which the covariance matrix of the damper model’s state variables does not become ill-conditioned. The damper model parameters can thereby be updated in real-time using measured data from the experimental substructure. The explicit MKR-α method is optimized and used in conjunction with the super element to efficiently integrate the condensed equations of motion of a large complex model having more than 1000 nonlinear elements, thus enabling multi-axis earthquake and wind hybrid nonlinear simulations to be performed in real-time. An adaptive servo-hydraulic actuator control scheme is used to enable precise real-time actuator displacements in the experimental substructure to be achieved that match the target displacements during a RTHS. The IT real-time architecture for integrating the components of the framework is described. To assess the framework, 3D RTHS of the 40-story structure were performed involving multi-axis translational and torsional response to multi-directional earthquake and wind natural hazards. The RTHS technique was applied to perform half-power tests to experimentally determine the amount of supplemental damping provided by the damped outrigger system for translational and torsional modes of vibration of the building. The results from the study presented herein demonstrate that RTHS can be applied to large nonlinear large structural systems involving multi-axis response to multi-directional excitation.
Keywords: Real-Time Hybrid Simulation, 3D Nonlinear Models, Rate-Dependent Nonlinear Devices, Multi-Directional Natural Hazards
Authors: Cao, L., Marullo; T., Al-Subaihawi; S., Kolay; C., Amer; A., Ricles, J.; Sause, R.; and Kusko, C. S.
DOI: 10.3389/fbuil.2020.00107
Abstract: The NHERI Lehigh Experimental Facility, as part of the NSF-funded Natural Hazards Engineering Research Infrastructure (NHERI) program, was established in 2016 as an open-access facility. This facility enables researchers to conduct state-of-art research on natural hazard mitigation in civil infrastructure systems, including high-performance numerical and physical testing to improve the resilience and sustainability of the civil infrastructure against natural hazards. The facility has the unique ability to conduct real-time multi-directional hybrid simulation (RTHS) on large-scale structural systems using 3D non-linear numerical models combined with large-scale physical models of structural and non-structural components. The Lehigh Experimental Facility possesses testbeds that include a lateral load-resisting system characterization testbed, a non-structural component multi-directional dynamic loading simulator, full-scale and reduced-scale damper testbeds, a tsunami and storm surge debris impact force testbed, and a soil-foundation structure interaction testbed. This paper describes the infrastructure and capabilities of the NHERI Lehigh Experimental Facility. Developments by the facility in advancing large-scale RTHS are detailed. Examples of research projects performed by users of the facility are then provided, including large-scale RTHS of steel frame buildings with magneto-rheological (MR) dampers and non-linear viscous dampers subject to strong earthquake ground motions; 3D multi-hazard large-scale RTHS of tall steel buildings subject to multi-directional wind and earthquake ground motions; characterization of a novel semi-active friction device based on band brake technology; and testing of cross-laminated timber self-centering coupled wall-floor diaphragm-gravity systems involving multi-directional loading.
Keywords: Experimental Facility, Real-Time Hybrid Simulation, Multi-Directional Loading, Natural Hazard Mitigation
Authors: H.-M. Huang, X. Gao, T. Tidwell, C. Gill, C. Lu and S. Dyke
DOI: 10.1145/1795194.1795205
Abstract: Real-time hybrid testing of civil structures, in which computational models and physical components must be integrated with high fidelity at run-time, represents a grand challenge in the emerging area of cyber-physical systems. Actuator dynamics, complex interactions among computers and physical components, and computation and communication delays all must be managed carefully to achieve accurate tests. In this paper we present a case study of several fundamental interlocking challenges in developing and evaluating cyber-physical systems for real-time hybrid structural testing: (1) how physical and simulated components can be integrated flexibly and efficiently within a common reusable middleware architecture; (2) how predictable timing can be achieved atop commonly available hardware and software platforms; and (3) how physical vs. simulated versions of different components within a system can be interchanged with high fidelity between comparable configurations. Experimental results obtained through this case study give evidence of the feasibility and efficacy of these steps towards our overall goal: to develop a Cyber-physical Instrument for Real-time hybrid Structural Testing (CIRST).
Keywords: Real-Time Hybrid Testing, Cyber-Physical Systems, Middleware Architecture, Actuator Dynamics
Authors: J. Orr, J. Condori, C. Gill, S. Baruah, K. Agrawal, S. Dyke, A. Prakash, I. Bate, C. Wong, and S. Adhikari
DOI: 10.1145/3394810.3394824
Abstract: Elastic scheduling allows for online adaptation of real-time tasks' utilizations (via manipulation of each task's computational workload or period) in order to maintain system schedulability in case the utilization demand of one or more tasks changes. This is done currently by assigning each task a utilization (and therefore period or workload) from within a continuous range of acceptable values. While this works well for anytime tasks whose quality of service improves with duration or for tasks that can run at any rate within a given range, many computationally-elastic tasks have a specific workload for each distinct mode of operation and therefore cannot perform arbitrary amounts of work. Similarly, some period-elastic tasks must run at specific (e.g. harmonic) rates. Therefore, a discrete set of candidate utilizations per task must be accommodated in such cases. This paper provides a new elastic task model in which each task has a discrete set of possible utilizations (instead of a continuous range). This allows users to specify only relevant candidate periods and workloads for each task. The discrete nature of this model also allows each task to modify its workload and/or its period when changing its mode of operation, instead of adapting in only one dimension of task utilization. Elastic tasks thus can exploit both period elasticity and computational elasticity. This greatly increases both the diversity of adaptations available to each task and the kinds of real-time tasks relevant to elastic scheduling.We use the real-world example of real-time hybrid simulation as a motivating application domain with discretely computationally-elastic, period-elastic, and combined-elastic parallel real-time tasks under the Federated Scheduling paradigm. We prove the scheduling of these tasks to be NP-hard, and provide a pseudo-polynomial time scheduling algorithm. We then use this scheduling algorithm to implement the first virtual real-time hybrid simulation experiment in which discrete elastic adaptation of platform resource utilizations enables adaptive switching between controllers with differing computational demands. We also study the effects of scheduling tasks with discretized vs. continuous candidate utilizations.
Keywords: Elastic Scheduling, Real-Time Hybrid Simulation, Discrete Utilizations, Federated Scheduling
