Specialist heavy lifting contractor Bigge Crane & Rigging, of San Leandro, California planned to use computer-controlled Hydrospex strand jacks to precision lift the 2,000USt (1,800t) steel span off a barge to a height of approximately 200ft within tolerances of 1/32in.
At the Oakland side (to the east), where the Skyway bridge deck has already been constructed, Bigge said the strand jacks would mounted on a mobile jacking platform that will be 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 has constructed two steel lifting towers, founded on piles driven into the bay for this purpose.
Bigge was to furnish two girders that span 125ft across the top of this lifting tower and strand jacks were to be mounted on top of a mobile jacking platform that sits on the girders. Both of Bigge’s jacking platforms are capable of synchronised eight-inch longitudinal and transverse movement.
At the Oakland end, Bigge is using four strand jacks, each of which has a lifting capacity of 365USt. 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 235USt lifting capacity will be used. These jacks have 19 wire rope strands, each 0.62 inches in diameter.
“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 Pete Ashton, Bigge vice president major projects.
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 strand jack technology to raise the sunken Russian Kursk submarine in 2002.
The first transition span, for the eastbound carriageway, was scheduled to be lifted on or around 16th January. The second span, parallel to the first, to carry the westbound carriageway, is scheduled to be lifted into place in June.
