FABRICATION AND CONSTRUCTION OF SELF ANCHORED SUSPENSION BRIDGE SAN FRANCISCO OAKLAND BAY BRIDGE

The signature span of the new Eastern Spans of the San Francisco Oakland Bay Bridge is an asymmetric Self Anchored Suspension (SAS) Bridge. The SAS spans a total of 565 m, with a 385m main span and a 180 m back span. Dual steel box girders are suspended from an inclined cable system supported on a single tower. The tower is comprised of four steel shafts inter-connected with shear links along its height. The unique configuration of the SAS presented challenges in the fabrication and construction. Unlike a traditional suspension bridge with parallel cables anchored into the ground, the SAS has a single 3-dimensional cable that is anchored into the east end of the box girder, passes over the tower top, and loops around saddles at the west pier. Each Parallel Wire Strand (PWS) has its own anchorage, which is detailed into the framing that transmits the entire cable force into the box girders. Because the cable tension is carried by the box girders, it was necessary to erect a temporary bridge to support the box girders during their erection, and then to construct the cable on the completed girders. During load transfer from the falsework to the suspension system the bridge compressed by 300 mm, requiring advance positioning of the tower top, the box girders, the bearings and the cable bands to fit the final geometry. Geometric control of the fabrication and construction went from the global level to the detailing, and throughout the stages of erection. Surveys at the fabrication yard and on site monitored the tower shaft plumbness and twist, box girder cambers, cable band twists, suspender inclinations. This paper discusses the challenges faced by the Design team, the Contractor and the Owner, and innovative solutions that were developed during the construction of this unique structure.