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Bay Bridge Info

The Self-Anchored Suspension Span (SAS) TOWER

SAS Lifts

CONSTRUCTION UPDATE: Your eyes are not playing tricks on you; the Self-Anchored Suspension (SAS) tower is tilting! But it’s only temporary and there’s a good reason for the leaning tower of the Bay Bridge. As the SAS cable will be anchored into the eastern end of the roadways, the cable will naturally pull to the east. So to properly balance the main cable during installation, crews in September pulled the top of the permanent tower 518 mm to the west, using temporary cables anchored into the bedrock of Yerba Buena Island. Once the cable is in place, the tower will be released to stand up straight once again.

The single, elegant tower is composed of four separate pentagonal legs, each of which is made up of five vertical sections or lifts, connected by shear link beams. The faceted forms of the tower legs are tapered and slender to enhance their appearance and to allow light to permeate through the interior of the tower and between the legs.
 
The leg sections are floated on barges to the construction site and erected one at a time. The barge, equipped with rails, positions itself on the open east side of the erection tower. Strand jacks positioned atop the erection tower lift the top of the tower segment, while a winch-assisted tipping cart stabilizes the bottom as it moves down the rails, pivoting from a horizontal to a vertical position. The strand jacks then lift the segment off the barge and into position inside the erection tower. To keep the barge steady while accommodating the shifting weight of the tower leg, thousands of gallons of ballast water are pumped from one side of the barge to the other through interior bulkheads.
 

Once the tower leg is vertical, crews detach the pin assembly connecting it to the barge; at that point it is only suspended by the strand jacks, which can hoist 1,455 tons/2.9 million pounds. The first sections are placed onto the tower’s massive marine foundation. These initial segments are slipped onto 150 steel dowels sticking out of the foundation, and fastened with 424 large anchor rods. When sections are stacked on top of each other, they are bolted together using splice plates. The 456 ton cable saddle at the top of the tower is the largest for a suspension bridge.

 
As sections are placed, workers attach cross bracings and shear link beams. Shear link beams, which connect the tower’s four independent legs, are designed to move independently to absorb seismic energy during an earthquake and to protect the tower from catastrophic damage. The damaged beams can be removed and replaced.
 
The SAS tower is nearly complete, with only the tower cap to be set on the top once the span’s single cable has been placed. The single tower is taller than numerous other Bay Area landmarks, including San Francisco’s Coit Tower (210 feet), the Campanile at U.C. Berkeley (307 feet) and the Tribune Tower (310 feet) in Oakland.
 

For more information about the SAS tower, view the fact sheets and press releases in the “Related Resources” section of this page.

Follow the progress of the SAS on the SAS Construction Page. 

Follow the action with the Construction Cameras.

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