Seismic Assessment and Retrofit Concepts of the BART Transbay Tube

Abstract

The Bay Area Rapid Transit (BART) system's Transbay Tube is 3.6 miles long and lies at the bottom of the San Francisco Bay, at a maximum depth of 132 feet below mean sea level. The tube is constructed of 57 segments with an average segment length of 330 feet. A ventilation structure is located at each end of the Transbay Tube — the San Francisco Ventilation Structure and the Oakland Ventilation Structure — and each is connected to the tube by a seismic joint. The Transbay Tube is a critical link in the BART system and a key system element analyzed as part of the BART Seismic Retrofit Program. Since the tube is submerged, it is important to ensure the structural integrity of the tube and the associated ventilation structures and seismic joints for the safety of passengers and BART personnel. Furthermore, for BART to provide an adequate level of post-earthquake transportation service to the public, satisfactory seismic performance of the tube is critical during any future strong earthquake in the Bay Area.