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.
Bigge strand jacks raise Bay Bridge deck
The first transition span, carrying the eastbound carriageway, was lifted into place overnight on 7/8 February this year. The second span, which will carry westbound traffic, also took just 10 hours to lift in an overnight operation on 29/30 August.
Each transition of the span sections – called tubs – were lifted to a height of approximately 200 ft (61m) within tolerances of 1/32 of an inch (0.8mm).
To lift such a heavy weight so precisely, Bigge used computer-controlled Hydrospex strand jacks.
For each lift, the strand jacks raised the load at speeds of up to 30ft per hour. During the lifts, the tubs were maintained with an eighth of an inch of the required attitude. Given that the tubs are 200ft long by 85ft wide, computerised 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 US ton lifting capacity, were mounted on a mobile jacking platform supported by a pair of 60ft girders, cantilevered 28ft 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 125ft 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.
Bigge strand jacks up close
All of the jacks were synchronized for simultaneous operation and load control within 1/32in.
Each tub was lifted from a barge that Bigge had used to transport them from Portland, Oregon, 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 trailers (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 degrees.
As on the first lift, now the second tub is raised to its final elevation, a temporary support tower has been skid under it at the Oakland (east) end 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 6ft (2m). The San Francisco (west) end of the tub is being supported by another temporary tower until the suspension bridge is constructed.
“To lift a 2,000 US ton load that is 200ft long and 85ft wide to a height of 200ft 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.”
Settlemeier said that the job also holds special significance for another reason. “My grandfather Henry Bigge, who founded this company 90 years ago, hauled the steel that built the Golden Gate bridge in the 1930s.”
The New Bay Bridge is expected
to cost $6.3 billion and be completed in 2012.
