Seismic retrofit for BART

摘要

Seismic preparedness in California has found urgent concern for BART, the Bay Area Rapid Transit system in Northern California. Several vulnerabilities to the region's ever-threatening seismic activity have been found with concern in particular for the system's Transbay Tube. The consequences of any damage repair outage or rupture of the structure would have by far, the greatest impact. T&TNA Editor Shani Wallis reports the causes of concern and the program being developed to mitigate potential seismic effects. At 3.6 miles (5.75km) long, the steel-hulled, reinforced concrete-lined crossing of San Francisco Bay remains one of the longest immersed tube tunnels in the world and one of its longest continuous rigid structures. Built in the 1970s, the Trans-bay crossing comprises 57 elements of about 330ft (100m) long, all welded together and attached either side to the San Francisco and Oakland vent structures. Inside there are two running track galleries and a central emergency/service gallery. Designed originally by Parsons Brincker-hoff/Tudor/Bechtel Joint Venture (PBTB), the tube lies up to 100ft (30m) below the Bay's mean sea level and was built according to state-of-the-art seismic understanding of the time.