BART San Francisco Transition Structure and Transbay Tube Uplift Seismic Retrofit - San Francisco, CA
As part of the BART Earthquake Safety Program, the San Francisco Transition Structure (SFTS) Project involves retrofit of the seismic joints connecting the BART Transbay Tube to the San Francisco Transition Structure (SFTS). The joints were originally designed (40+ years ago) for much less deformation capacity than is currently predicted. The retrofit tasks include verification of estimated seismic joint movements under seismic loading, including potential landslide and liquefaction effects, and development of retrofit measures and/or introduction of new joints to accommodate the associated movements. During major earthquake events, the Transbay Tube will potentially be axially overstressed, and it may have a delayed uplift effect. After the earthquake, it may be uplifted at a few critical locations. This vulnerability has to be resolved.
AMC performed structural analyses to QA/QC SC Solutions’ ADINA nonlinear time-history analyses in estimating the seismic joint movement. AMC also assisted Fugro West in SASSI analysis to obtain soil impedance of the Transition and Tube structures as input to the Global model. To develop the retrofit scheme to resolve the Transbay Tube’s axial overstress, our simplified, accurate, and robust ADINA model was used to perform many parametric studies. AMC developed an ADINA FEM model of a typical transition joint section between tube segments for stress evaluation. AMC also supported PB in evaluating the capacities of each component along the axial load path from the Transbay Tube to the SFTS, and to the bored tunnel; and in developing retrofit design options. AMC performed ADINA nonlinear static analysis to evaluate uplift effect of the tube due to ground offset.