Bigge Crane & Rigging Uses Alternative Lifting Technology in Bay Bridge Project Phase

By Robert Carlsen

SAN FRANCISCO--Construction of the new San Francisco Oakland Bay Bridge reached a milestone at press time when the first transition span, linking the concrete Skyway bridge deck section with the yet-to-be-built suspension bridge, was being lifted into place using trail-blazing alternative lifting technology.

Specialist heavy lifting contractor Bigge Crane & Rigging of San Leandro is using computer-controlled Hydrospex strand jacks to precision lift the 2,000-ton steel span off a barge to a height of approximately 200 ft. 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 United States, said Pete Ashton, Bigge's vice president of major projects.

At 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-ft. girders, cantilevered 28 ft. off the bridge deck.

At the San Francisco side (to the west), main contracting consortium Kiewit-FCI-Manson has constructed two steel lifting towers, founded on piles driven into the bay for this purpose. Bigge will furnish two girders that span 125 ft. across the top of this lifting tower and strand jacks will be mounted on top of a mobile jacking platform that sits on the girders. Both of Bigge's jacking platforms are capable of synchronized 8-in. longitudinal and transverse movement.

At the Oakland end, Bigge is using 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 in. 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.

"No traditional crane, particularly a barge-mounted one on the water, could do this job with the required combination of lifting capacity and precision," said Ashton.

Ashton added that this is the first major project on which Bigge has used its new strand jack equipment since becoming 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 second transition span, parallel to the first, to carry the westbound carriageway, is scheduled to be lifted into place in June.

Each lift will take approximately 10 hours, as the strand jacks raise the load at speeds of up to 30 ft. per hour. During the lifts the tubs, as these transition spans are called, will be maintained with an eighth of an inch of the required attitude. Given that the tubs are 200 ft. long by 85 ft. wide, this can only be achieved by computerised monitoring, said Ashton.

On each lift, once the tub is lifted to elevation, a temporary support tower will be skidded under the tub for support until the concrete joint with the existing Skyway is poured and cured, filling a gap of some 6 ft. The San Francisco (west) end of the tub will be supported by another temporary tower until the suspension bridge is constructed. When each of these towers is skidded into position, Bigge will lower the tub onto the towers and adjust the tub for the exact cross fall and longitudinal elevation. After the tub is secured to the temporary support towers, the San Francisco end lift system will be dismantled. The Oakland end will be left in position three months while the concrete closure pour cures.

Bigge is also contracted to load the tubs onto a barge in Portland, where they have been fabricated, and ship them to the site. The first one was loaded onto the barge on Dec. 29 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 followed along the coast line to San Francisco Bay, traveling under the Golden Gate Bridge to the site wharf in Oakland.

"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."