Computer-controlled strand jacks set to lift Bay Bridge transition
18 April 2008
The first transition span of the new San Francisco Oakland Bay Bridge is being lifted into place this month using computer-controlled Hydrospex strand jacks. ACT reports.
Linking the concrete skyway bridge deck section with the yet-to-be-built suspension bridge, the transition span will be put into place by heavy lifting contractor Bigge Crane & Rigging, of San Leandro, CA.
Bigge has engineered a precision lift for the 2,000 ton steel span off a barge to a height of approximately 200 feet within tolerances of 1/32 of an inch.
On the Oakland side (to the east), where the skyway bridge deck has already been constructed, the strand jacks will be mounted on a mobile jacking platform that will be supported by a pair of 60 foot girders, cantilevered 28 feet off the bridge deck. On the San Francisco side (to the west), main contracting consortium Kiewit-FCI-Manson has constructed two steel lifting towers. Bigge will furnish two girders that span 125 feet across the top of the lifting tower, and strand jacks will be mounted on top of a mobile jacking platform that sits on the girders.
At the Oakland end, Bigge plans to use four strand jacks, each of which has a lifting capacity of 365 tons. Each jack pulls on a bundle of 31 strands. Each rope is 0.62 inches (15.7mm) in diameter. At the San Francisco end, six jacks of 235 ton lifting capacity will be used. These jacks have 19 wire rope strands, each 0.62 inches in diameter. All of the jacks are synchronized for simultaneous operation and load control within a 1/32 inch.
Bigge is the exclusive representative of Hydrospex, the Dutch manufacturer that also supplied the strand jack technology that raised the sunken Russian Kursk submarine in 2002.
The first transition was set to be lifted by mid January with the second span, parallel to the first, scheduled for early summer 2006.
Bigge also was contracted to load the transition spans, or tubs as they are called, onto a barge at Portland OR, where they were fabricated, and ship them to the site. The first one was loaded onto a barge in late December using 48 axle lines of Scheuerle self-propelled hydraulic modular trailer (SPMT). The barge was then towed out of the mouth of the Columbia River to the Pacific Ocean where it traveled to the San Francisco Bay.
“Transporting and lifting such a super-heavy load to such a height is a significant operation,” said Weston Settlemier, president of Bigge Crane & Rigging. “We are unaware of such a heavy load ever being lifted so high anywhere in the United States. However, we have engineered a solution, using our own equipment, which is the very latest in computer- controlled lifting technology that makes this job possible.”