A quick thought on the new Bay Bridge

Last night I caught The Bridge So Far - a Suspense Story on PBS. The documentary about the Bay Bridge explores the history of the old bridge and the three ring circus that has been the building of the new eastern span. The new span is well on its way, and I enjoy seeing it progress, the Oakland Alameda Ferry provides a nice view. However entertaining all the politicking around the building of the bridge is, I wish The Bridge So Far had spent a few more minutes on explaining the working of the Self Anchored Suspension (SAS) design at the western end of the new span. But that's what the internet is for.

The Bay Bridge project site itself has a surprisingly informative .pdf fact sheet about the SAS. When completed, projected for 2013, the western part of the eastern span of the Bay Bridge will be the world's longest SAS. A traditional suspension bridge such as the Golden Gate Bridge has two cables which run across the tops of the towers and are anchored in the land at each end. The SAS has one cable which will start at the eastern end of the section, go over the single tower, wraps around the bridge decks at the western footing, runs back over the tower and is anchored to the bridge deck at the eastern end. Fascinating stuff, when the bridge is finished I'm sure my favorite civil engineering writer Henry Petroski will have something interesting to say about it.