THE SAS MAIN CABLE
CONSTRUCTION UPDATE (December 19, 2011): The Self-Anchored Suspension Span (SAS) celebrates a major milestone this week as workers prepare to install the first strand of the main cable for what will be the world’s longest SAS. The 2,047-foot-long SAS is the signature element of the San Francisco-Oakland Bay Bridge’s new East Span.
While the unprecedented work to install the main cable will be visible from the existing bridge, motorists are urged to keep their eyes on the road as maintaining safe driving conditions is paramount. Progress on the cable installation can be viewed safely from the new publicly-accessible interpretive display located on Treasure Island and online via construction cameras.
The SAS’s single, nearly 1-mile-long cable is anchored into the east end of the roadway, traveling up and over the single tower to wrap around the west end before traveling back up and over the tower to anchor back into the east end; in other words, the 2.6-foot-diameter cable acts like a giant, unbelievably strong sling; the cable’s diameter is also the largest for a self-anchored suspension span. The nearly mile-long cable is also the longest looped suspension cable in any bridge. The cable features 118 miles of 2 1/2-inch steel strands and more than 17,000 5mm wires, each of which can support the weight of a military grade Hummer. The cable weighs 5,291 tons or nearly 10.6 million pounds. Anchoring the main cable in the deck itself puts the span into compression and enables it to remain standing. In a traditional suspension span, tension created in the main cables is resisted by anchorages in the ground.
In late 2011, workers began erecting a temporary footbridge that will travel the path of the SAS cable, so iron-workers will have unfettered if precarious access to the cable as it is being placed. Once the SAS is finished, the suspenders connecting the cable to the bridge deck will be tightened and the bridge will be lifted off the temporary support structure, which will be dismantled.
Because the SAS cable will be anchored into the eastern end of the roadways, the cable will naturally pull to the east. In September, 2011, to properly balance the main cable during installation, crews pulled the top of the permanent tower 20.4" (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.
- Length of main cable: .86 miles/4,550 feet/1,387 meters
- Diameter of main cable: 31.2 inches 0.79 (meter)
- Weight of main cable: 10.6 million pounds (5,291 tons)
- Number of individual wires: 17,399
- Number of strands: 137
- Number of wires/strand: 127
- Diameter of each wire: 5mm
