The seismically vulnerable east span of California's San Francisco-Oakland Bay Bridge will be replaced with a dual eastbound and westbound parallel structure 3.6 km long. The Bay Bridge lies between the Hayward and the San Andreas Faults, which can generate magnitude 7.5 and 8.1 M earthquakes, respectively. Performance criteria require that the bridge be operational immediately after a 1,500-year-return-period earthquake from either of these two faults. Four distinct structures will make up the bridge crossing: a low-rise posttensioned concrete box girder near the Oakland shore, a segmental concrete box girder 2.4 km long, a self-anchored suspension signature span, and a posttensioned concrete box girder that connects to the east portal of the Yerba Buena Island tunnel. The single-tower asymmetric self-anchored suspension bridge was selected from a total of four design alternatives that were developed for the signature main span; these included two cable-stayed bridges and two self-anchored suspension bridges (each bridge type included single-tower and dual portal tower alternatives). Each design alternative was evaluated on the basis of its seismic response, construction cost, and aesthetic properties.
Samenvatting