The most expensive public works project in California history, a $6.4-billion replacement for the eastern span of the 76-year-old San Francisco-Oakland Bay Bridge, may not be completed in time for its scheduled Labor Day opening in September.
California Department of Transportation (Caltrans) engineers are trying to figure out why 32 anchoring bolts (9 to 24 feet long) popped out last month when 96 of the 288 steel rods were stress tested. Now Caltrans officials are being stress tested as they not only wrestle with finding a cause, but ponder what solutions might be available and at what cost.
The Bay Bridge is actually a pair of spans connecting San Francisco and Oakland that meet in the middle at Yerba Buena Island. The bolts that snapped connect steel earthquake safety shear keys to the deck of the eastern span and large concrete cap. They are not readily accessible, which will complicate any corrective action.
Early betting on the cause of the defective bolts favors “hydrogen embrittlement,” which occurs when hydrogen atoms work their way into spaces of the steel’s molecular structure. Original speculation was that it occurred during the manufacturing process, but some observers wonder if the culprit is simply rain seeping in through microscopic cracks.
Whatever the problems are, metallurgists and engineers told the Contra Costa Times that they could, and should, have been avoided. “There is a lot of technology out there that could have been used to prevent this from happening,” private engineering consultant Louis Raymond told the newspaper. They raised questions about the technology used to create the rods, the manufacturer’s testing protocol, subsequent tests by subcontractors and handling of the bolts during assembly.
Steve Heminger, executive director of the Metropolitan Transportation Commission that manages the Caltrans-owned bridge, told the SF Examiner, “Given the significant number of the failure of the bolts, I think there clearly was a quality-control failure.”
The bolt problems are the latest in a series of mishaps that have haunted the bridge during its lengthy construction process. Allegedly faulty welds on the elevated skyway and the suspension span were laboriously reviewed, and authorities ultimately judged them to be adequate.
The Loma Prieta earthquake on October 17, 1989, caused a section of the upper deck of the bridge to collapse into the lower deck below. It was fixed in a month but plans began then to retrofit the bridge.
A series of Sacramento Bee stories the past two years have raised questions about structural integrity testing of the new span’s foundation tower. Caltrans dismissed the concerns, but according to the Bee, the independent Legislative Analyst's Office will report on its own investigation by June 30.
Once completed, work will immediately begin on disassembling the bridge span being replaced. Estimates are that it could take seven years to complete at a cost of more than $240 million.