Which Indiana bridges are the most susceptible to earthquakes? Purdue researchers have set out to find the answer.

The Indiana Department of Transportation (INDOT) is responding to the seismic risk presented by the Wabash and New Madrid faults with a multi-year effort, started in 2018, to enhance the seismic response and training of INDOT personnel. Over the last three years, the effort has focused on assessing the seismic vulnerability of the state's bridge network and empowering INDOT's maintenance database (BIAS) to conduct rapid seismic vulnerability assessment.

The work has been conducted through the Joint Transportation Research Program (JTRP), led by Purdue Civil Engineering and Mechanical Engineering Professor Shirley Dyke.

"Indiana needs powerful tools to determine which of its thousands of bridges are most vulnerable to earthquakes in regard to the seismic hazard in the state, and may be good choices to bring up to the latest standards," Dyke said. "This need is about to be addressed, thanks to the research at the Lyles School of Civil Engineering."

Dyke's team and collaborators from Purdue and Notre Dame universities have been developing an automated tool, INSAT, that can assess the seismic vulnerability of Indiana's bridge inventory. The program uses simple dynamic models, an understanding of typical bridge behavior and seismic hazard to rapidly assess bridge vulnerability. It color codes each bridge as either low, moderate or high vulnerability, with high meaning that particular bridge should be prioritized for attention.

INSAT is linked to BIAS and supplemented at this time with additional information from a detailed analysis and data from bridge drawings. One of the main recommendations from this study is in the form of additional data that if included in BIAS would empower INDOT to carry out a rapid seismic vulnerability assessment with INSAT.

Since January of 2018, Dyke's team has conducted a detailed analysis of 100 bridges of varying age, size and design. They created models to understand potential vulnerabilities across the inventory. Their focus was on bridges in the Wabash Valley Seismic Zone, located in the southwestern portion of Indiana.

"This project had a clear need and will serve as an invaluable asset to the Indiana Department of Transportation supporting their decisions as they ask which bridges need the most urgent attention," said Civil Engineering graduate student Alana Lund.

Around 4% of bridges the team examined ranked high priority for retrofitting to decrease their seismic vulnerability.

"In order for us to understand the criteria to use, we recreated these bridges and simulated them ourselves," said Civil Engineering graduate student Corey Beck. "From there, we've been able to identify specific vulnerability levels for different types of bridges along with strategies to improve them."

Civil Engineering graduate student Leslie Bonthron said their research determined that the greatest determining factor for a bridge's vulnerability was its substructure, no matter if it was reinforced concrete, pre-stressed concrete, or concrete and steel.

"The older the wall substructures, the more vulnerable they were to seismic activity," Bonthron said. "And, with this new tool, an engineer will be able to assess just how vulnerable a bridge is with a simple click of a button."

"The team is also making use of machine learning methods to populate the data fields that enable the tool to run robustly," said Civil Engineering graduate student Xin Zhang.

Dyke said the team expects to finalize and submit their work to INDOT before the end of 2020.