Seismic Retrofit of San Francisco Bay-Area-Rapid-Transit Aerial Stations

Located along the border of the Pacific plate and the North American plate, the state of California is one of the most seismically active regions in the world. Since the San Francisco Bay Area Rapid Transit (BART) carried the first passenger in 1972, it is considered as the most vital transportation link for the Bay Area with more than 360 000 daily ridership. Several major fault lines cross or are parallel to the BART structures, including Hayward fault and Concord fault. A recent study estimated that there is a 62% probability of a magnitude 6,7 or greater earthquake in the Bay Area in the next 30 years. Compared with the structure originally designed half a century ago, higher standards are required for the structures. Meanwhile, engineering societies now have much better understanding of the structure's seismic performance. All of the above factors prompt the development of the BART Earthquake Safety Program (ESP). The paper covers the seismic evaluation and retrofit of a total of 11 aerial stations within the program. The stations are located along "A-line", "C-line", and "R-line" of the BART system. Most of the stations are retrofitted to meet the safety performance requirement, whereas three stations have been additionally evaluated and designed to meet the operability performance requirement. Analysis approaches, seismic vulnerability of as-built stations, and retrofit measures proposed are presented in detail in the paper.