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San Francisco-Oakland Bay Bridge Update

Temporary SAS Support Structures Rise From the Bay

Bay Bridge’s Self-Anchored Suspension Span Continues to Take Shape

Photos: Peter Beeler (click to enlarge)

September 23, 2008
Temporary support structures have begun to rise out of the San Francisco Bay at Yerba Buena Island, as construction moves forward on the Bay Bridge’s Self-Anchored Suspension (SAS) Span. Part of the San Francisco-Oakland Bay Bridge Seismic Retrofit Projects, the SAS will be the most striking element of the retrofitted bridge. This section of the East Span will not only feature the world’s largest Self-Anchored Suspension bridge, it will also be the first bridge of its kind built with a single tower.

To build the SAS, crews must first construct a temporary bridge to support work on the permanent span. While the SAS will only have three support foundations, the temporary structure will have seven. The first temporary support on Yerba Buena Island has already been built, and the second support is under construction. Crews will erect the temporary steel truss support foundations, including a steel truss roadway support and tower.

While drivers on the existing East Span will see these temporary structures, they look nothing like the final bridge that will grace the Bay Area with an elegant and sweeping design. While the temporary work includes steel trusses and multiple support structures, the SAS itself will be a graceful white span with only three support foundations.

Building a different kind of suspension bridge requires a different kind of process. Traditional suspension span construction starts with the main cable and suspender cables being placed, and then the roadway being built. Traditional suspension spans also have two main cables that are anchored into the foundations. The SAS has only one cable that is anchored at the east end of the span, wraps around the west end, and then anchors back into the east end. Because of this unique design, the roadway must be built first.

As workers build the temporary supports, crews will begin erecting the permanent roadway and signature tower for the SAS. Assisting this endeavor will be a barge equipped with a 300-foot-long boom that will be visible to drivers on the Bay Bridge.

In addition to temporary foundations and roadway, crews will erect a footbridge that will travel the path of the SAS cable, so ironworkers can work on the cable as it is placed. Once the permanent SAS span is in place, the temporary supports will be removed, shifting the weight off the temporary foundations and onto the cables.