Transbay Transit Center, Seismic Soil-Structure Interaction Analysis
San Francisco, Calif.

We have started seismic soil-structure interaction analysis for the Transbay Transit Center. We are providing structural design services to Pelli Clarke Pelli Architects for the new Transit Center, which will feature a 5.4-acre public park on the roof of the new station. The Transit Center is more than 1,500 feet long and has a basement up to 55 feet deep. Because of the basement’s dimensions, the soil condition and the seismic free-field ground motion (ground motion in absence of the structure) can vary along its length and depth. Motion at the base of the superstructure will differ from motion at basement levels, and ground motion at separate ends of the structure can differ. Possible interactions with adjacent structures and the effects of the changes in the box geometry complicate the seismic behavior further and will also be analyzed to develop a design that minimizes motion effects and maximizes safety. We have begun 2-D soil-structure interaction analysis for the design of the superstructure and the basement box, with help from sub-consultant Fugro West.