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Field Instrumentation for Evaluation of the I-64 Sherman Minton Bridge

In-service inspection of the Sherman Minton Bridge in southern Indiana identified cracking in the steel at several locations on the fracture-critical tie girders. Dr. Robert Connor led a group of researchers from Purdue University's S-BRITE Center in completing a Fitness for Service (FFS) evaluation of the tie girder welds on the bridge, as well as a robust, long-term, remote monitoring program where member stress, pier tilt, wind speed and direction, and ambient and steel temperature data were collected over several months.

Dr. Robert Connor led a group of researchers from Purdue University’s S-BRITE Center in completing a Fitness for Service (FFS) evaluation of the tie girder welds on the Sherman Minton Bridge, as well as a robust, remote monitoring program where member stress, pier tilt, wind speed and direction, and ambient and steel temperature data were collected over several months.  Using results from material test data, residual stress profiles, and linear elastic fracture mechanics (LEFM) models, S-BRITE researchers generated a failure assessment diagram (FAD) determining whether cracks and crack-like flaws in certain details of the Bridge were within an acceptable range, meaning the bridge would be expected to remain stable.

The field testing included the installation of a long-term data acquisition system.  This system contained uni-axial strain gages located at various locations on the ties and floor beams.  Thermocouples were also installed at a few locations to measure the temperature of the steel and an anemometer measured wind speed and direction.  Additional temperature monitoring of the steel and ambient air was carried out during retrofit operations in the event the steel temperature dipped below that recommended for retrofit work to continue, as well as providing an understanding of how the bridge responded to thermal loading.  The instrumentation was focused on the upstream and downstream ties of span 2.  The primary intent of the monitoring was to capture in-service live load stress ranges in predetermined areas of interest.  Rainflow cycle counting was used to construct histograms to evaluate the fatigue performance of the structure and to estimate the remaining fatigue life.

Additionally, at the request of INDOT, S-BRITE Center researchers also carried out bridge inspector performance tests.  Plates with and without flaws were placed on the bridge simulating a true inspection scenario.  Bridge inspectors were asked to inspect the plates and note any flaws found using their method of expertise (i.e., ultrasonic, mag-particle, etc.).  INDOT used the results from the performance test to determine which inspectors would be allowed to inspect the Sherman Minton Bridge.