2-D Seismic Soil-Structure Interaction Study, Transbay Transit Center

The Transbay Transit Center (TTC) will be located in downtown San Francisco, California, and will serve 11 transportation systems including the future High Speed Rail.  The proposed structure is 1,500 feet long, and consists of 6 stories, including below-grade trainbox and 5.4 acre rooftop park.  Series of two-dimensional seismic soil-structure interaction (SSI) analyses were performed, including fully-coupled direct solution approach as well as substructuring approach. “Scattered” motions, soil springs and dashpots were developed at different locations along the structure. Results of fully-coupled solution were used to validate substructuring approach. Results showed that the traditional approach of directly applying “free field” ground motions to the base of the structure do not capture kinematic and inertial effects for large, buried and flexible structures. Analyses showed adjacent structures in urban setting can have significant impact on structural response. Also, response of buoyant structures is considerably different than that of a typical structure.