SOIL-STRUCTURE INTERACTION ANALYSIS FOR BURIED STRUCTURES IN SOFT, SLOPING SOILS - BART SAN FRANCISCO TRANSITION STRUCTURE

摘要

A case history is presented for soil-structure interaction (SSI) analyses of the San Francisco Transition Structure (SFTS), a massive rigid structure which is part of the BART Transbay Tube (TBT) system in California. A methodology was developed to study the complex SSI problem for the SFTS. This methodology may be applicable for relatively large, buried structures in soft soils and sloping ground susceptible to movement during the design earthquake. The SSI studies included 3D SASSI analyses to develop far-field impedances due to dynamic vibrations, and FLAC 3D analyses to develop near-field nonlinear springs. A methodology was developed to use the near-field spring and far-field impedances obtained from SSI analyses in a global model that included the SFTS as well as the TBT that connects to it. Displacement time histories to drive the global model were also developed as part of this study. Scatter motions were obtained at the base of the SFTS as well as along the TBT. An approach of transitioning of the scatter motions to the free-field motions along the TBT was developed. Permanent drifts due to movement of the slope around the SFTS were incorporated in the development of ground motions.