The Auburn-Foresthill Bridge is a 2,428 ft steel suspension bridge that links the towns of Auburn and Foresthill, California and was built in1973. While it is ranked 3rd in the U.S., it is the tallest bridge in California. The bridge is located in the seismically active Foothills fault zone and is supported by two 403 ft tall unconfined concrete piers. The seismic vulnerability of the bridge is critical in developing a retrofit strategy. This paper discusses the development of a 3D non-linear finite element model of bridge, the non-linear time history analysis, and the seismic performance of key bridge components. A detailed three-dimensional model of the bridge was constructed using the general purpose finite element program ADINA. The FE model includes nonlinearities in the material and geometry. Nonlinear plastic beam elements are used to simulate the behavior of the perforated and non-perforated elements in the superstructure and the piers. The non-linear plastic beam properties are obtained using SC Solutions’ section analysis program SPEMC. These superstructure non-linear plastic elements are able to capture global buckling of superstructure elements. The buckling behavior of these members was validated using detailed shell FE models for both perforated and non-perforated sections. The pier nonlinear plastic beam elements are able to capture concrete and steel reinforcement strains.

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