Specialist heavy-lifting contractor Bigge Crane & Rigging of San Leandro, Calif., has installed the second of a pair of 2,000-ton steel bridge deck sections on the new San Francisco-Oakland Bay Bridge.
This second mega-lift operation completes the transition spans between the concrete Skyway bridge on the Oakland side and a suspension bridge--not yet built--to Yerba Buena Island.
The first transition span, carrying the eastbound carriageway, was lifted into place overnight on Feb. 7-8 this year.
The second span, which will carry westbound traffic, also took just 10 hours to lift in an overnight operation on Aug. 29-30.
Each transition span section, called tubs, was lifted to a height of approximately 200 ft within tolerances of 1/32 of an inch. To lift such a heavy weight so precisely, Bigge used computer-controlled Hydrospex strand jacks.
For each lift, the strand jacks raise the load at speeds of up to 30 ft per hour. During the lifts, the tubs were maintained with an eighth of an inch of the required attitude. Given that the tubs are 200-ft long by 85-ft wide, computerized monitoring was essential.
At the Oakland side to the east, where the Skyway bridge deck has already been constructed, four strand jacks--each with a 365-ton lifting capacity--were mounted on a mobile-jacking platform 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 constructed two steel lifting towers, founded on piles driven into the Bay for this purpose. Bigge supplied the two girders that span 125 ft across the top of this lifting tower as well as six strand jacks (235-ton capacity) mounted on top of a mobile-jacking platform that sits on these girders. All of the jacks were synchronized for simultaneous operation and load control within a 1/32 in.
Each tub was lifted from a barge that Bigge had used to transport them from Portland, Ore., where they had been fabricated. For each of the transport operations, Bigge loaded the tub onto the barge using 48 axle lines of Scheuerle self-propelled modular trailer (SPMT). With bridge piers, erection towers and other obstacles, there was no space to bring in the barge at the correct angle under the bridge. Instead, Bigge was able to rotate the barge-mounted SPMT to turn the tub by the necessary 90?.
As on the first lift, the second tub is now raised to its final elevation, a temporary support tower has been skid under it at the Oakland end of it to hold it in place for three months until the concrete joint with the existing Skyway is poured and cured, filling a gap of some 6 ft. The San Francisco end of the tub is being supported by another temporary tower until the suspension bridge is constructed.
"To lift a 2,000-ton load that is 200-ft long and 85-ft wide to a height of 200-ft long is an operation that requires precise engineering and thorough planning," said Weston Settlemier, president of Bigge Crane & Rigging. "To do it twice is something special for us," he added.
"As a local company, we are very proud to have made such a contribution to this project," Settlemier said. "My grandfather Henry Bigge, who founded this company 90 years ago, hauled the steel that built the Golden Gate bridge in the 1930s. I am delighted that the tradition of Bigge's involvement in the construction of iconic structures in the Bay area continues today."
The new Bay Bridge is expected to cost $6.3 billion and be completed in 2012.