The Millard E. Tydings Memorial Bridge has carried Interstate 95 over the Susquehanna River between Cecil and Harford County since its opening in 1963. The structure consists of six lanes supported by a 14 span variable depth steel deck truss. The total structure length is 5,056 feet with a maximum span of 490 feet.
A live load test was conducted for the Bridge to provide model calibration for obtaining refined live load ratings for specific structural members and gusset plate connections. The field testing also addressed fatigue concerns at select locations through measurement of nominal stresses. A strategy was developed in conjunction with Ammann & Whitney, to obtain the most information within the confines of a single live load test. Intelligent Infrastructure Systems ‘ approach to the project followed the framework of Structural Identification, an ASCE-adopted six-step process which begins with the documentation and understanding of the structure and proceeds through finite element model development, experimental design, testing, data reduction, model calibration and finally utilization of model for simulations.
In this case, Intelligent Infrastructure Systems designed and implemented a live load test and obtained strain measurements on a cross section of floor system stringers and floor beams, as well as three complete cross-sections of the truss. Intelligent Infrastructure Systems then compiled and processed all of the collected measurements and used the results as the basis for a formal model calibration using advanced optimization algorithms. The project concluded with the utilization of the calibrated FE model to produce refined member loads under various loading scenarios, as well as provide for direct interpretation of data to better understand the complicated nature of the load path in this structural system.