After several delays, the first transition span of the new San Francisco Oakland Bay Bridge was lifted into place on February 7-8.
San Leandro, CA-based Bigge Crane & Rigging used computer-controlled Hydrospex strand jacks to lift the 2,000 ton steel span off a barge to a height of around 200 feet within tolerances of 1/32 of an inch.
Although strand jacks are not new technology, they have never been used on this scale before in bridge construction in the US, according to Bigge.
At the Oakland side (to the east), where the skyway bridge deck has already been constructed, the strand jacks were mounted on a mobile jacking platform supported by a pair of 60 foot girders, cantilevered 28 feet off the bridge deck.
Bigge used four strand jacks, each with a lifting capacity of 365 tons. Each jack pulls on a bundle of 31 strands and each rope is 0.62 inches (15.7mm) in diameter.
“No traditional crane, particularly a barge-mounted one on the water, could have done this job with the required combination of lifting capacity and precision,” said Pete Ashton, Bigge vice president of major projects.