San Francisco - Oakland Bay Bridge in California. Courtesy Wikipedia (left).
Transportation conceived the design for the new east span of the San-Francisco-Oakland Bay Bridge, the world’s longest self-anchored suspension bridge. The project was executed in collaboration with a joint venture team led by TY Lin International. A single 300-foot-high pylon tower stands between two five-lane roadways; the two main cables and wire rope suspenders drape from the tower and slant over the roadways to connect to their outer deck edges. Anchoring the cables into the roadway deck solved the problem of the Bay mud, a soft silty clay that cannot support the concrete anchorages of most suspension bridges. The bridge connects Yerba Buena Island and the viaduct to Oakland, replacing a cantilever bridge that was severely damaged in the 1989 Loma Prieta earthquake. The new bridge was designed for a magnitude-7.25 earthquake on the Hayward Fault and magnitude-8+ earthquake on the San Andreas Fault.
The Bay Bridge was the largest public construction contract in California’s history and one of the most challenging ever undertaken in the United States. The design process began with a competition between two bridge types: a suspension bridge and a cable-stayed bridge, each developed to a preliminary stage (30%) and compared for earthquake reliability, cost, construction risk and aesthetics. The bridge needed to be architecturally consistent with the twin suspension bridges to the east, the hills on both ends of the structure and the skyway to Oakland. A major challenge was the need to complete the structure before another major earthquake occurs, while maintaining traffic during construction.
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