Fifteen years after the Loma Prieta earthquake brought down part of the upper deck of the San Francisco-Oakland Bay Bridge and killing a motorist, a replacement structure is finally under construction. California’s highway authority Caltrans calculated that while the western side of the original 1936 bridge (from San Francisco to Yerba Buena) could be retrofitted to withstand the next quake, it would be cheaper and easier to replace the eastern section, which runs from Yerna Buena to Oakland.
The new 3.5km span will not be a single structure but a combination of bridges and viaducts, including the world’s first single tower suspension bridge (designed by TY Lin International) that may become as recognisable a landmark as the Golden Gate or Sydney Harbour bridges.
The whole project was valued in 2002 at $2.6bn, with one section alone – the Skyway viaduct, on the Oakland side of the bridge – costing $1.04bn, making it by far the largest single construction contract ever awarded by the state of California. This section was designed by Moffatt & Nichol Engineers.
Main contractor for the project is KFM – a joint venture of Kiewit Pacific, FCI Constructors Northern Division and Manson Construction. Work began in 2003 and is scheduled to complete in 2007.
Central to the construction work are 14 large Potain tower cranes that now line the route of the new bridge. These MD 560-40 cranes all have a height under hook of 47.2m (155ft). Maximum lift capacity of this model is 40t. The maximum possible jib length is 40m, where they can lift 3.6t. However, on this project jib lengths are 67m on two of the cranes, 62m on another two, 57m on six and 47m on the remaining four. The first unit was installed in July 2003 and the last one went up just last month, averaging one installation a month. The upper section of each crane was lifted onto its mast in a single 60t section by a barge crane, with each lift taking an average of one hour.
The Skyway comprises 452 precast concrete blocks, most of which are 7.6m long, 27.4m wide and 9.1m tall (25ft x 90ft x 30ft). Weights vary from 435t to 700t. These segments are being made in a precast yard, some 100km upstream in Stockton and shipped to the site by barge. Another Potain MD 560-40 is at work in this yard. And yet another one is on the dock for loading material onto the barges that service the bridge construction site.
The 14 cranes on the bridge itself are each footed on a pile-supported platform that stands 3m out of the water at high tide. Their foundations stand at intervals between the actual bridge piers and the cranes form a sentry alongside the route of the new viaduct, placing formwork and rebar and carrying out other lifting duties. The Skyway section carries the new roadway along parallel twin spans – one for each direction. The eastbound span is being built first and when it is completed the westbound one begins. Each span carries five lanes, which is no more than the old bridge, because the Yerba Buena tunnel limits the number of lanes. However, the new bridge includes space to drag off broken down vehicles, to keep traffic moving.
Each crane costs about $1.2 million. They were bought by the KFM contracting joint venture, although Cranes Today understands that Manitowoc Crane Group – Potain’s parent company – has given a buy-back guarantee to the customer. SI Equipment, the Potain distributor for California, is working closely with KFM, setting up the cranes and offering support in training and maintenance..
Under the construction plan, the old steel bridge will be demolished in 2007, with each section being dismantled and barged away for recycling.