Fixing broken bolts that are key to the Bay Bridge's ability to withstand a seismic shock will take months but should not delay its opening, California Department of Transportation officials said Wednesday.
Caltrans project manager Tony Anziano told the Metropolitan Transportation Commission that his agency would develop a work-around to secure the vital seismic stabilization equipment after heavy-duty bolts broke on the new $6.4 billion eastern span of the San Francisco-Oakland Bay Bridge.
But during questioning by commissioners, Anziano conceded that some uncertainty remains about the span's projected Labor Day weekend opening.
"Time is absolutely tight," Anziano said. "Everybody should acknowledge that there is risk" that the bridge opening might be delayed to ensure seismic safety.
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Caltrans will replace at least 32 bolts, and perhaps many others, attached to "shear keys." Shear keys are units that allow controlled lateral movement of the bridge in the event of a large quake.
The same type of bolts connected to bearings - another seismic control device - have not been found to be defective but are also considered suspect, according to Caltrans.
Overall, officials said, concerns involve 288 bolts.
The bolts, also referred to as rods, attach the four shear keys and four bearings between the easternmost pier of the new suspension span and the roadway above it. The devices were made by the Korean firm Hochang Machinery Industries, but the bolts were made in the United States, according to Caltrans. The agency did not identify the U.S. manufacturer.
Bearings and shear keys are massive steel devices nearly 6 feet tall. The broken bolts are 3 inches in diameter and up to 24 feet long. At the center of the shear key, a circular joint joins the suspension span to the pier much like a trailer hitch allows a load to sway laterally with some independence, yet remain secured to a pickup truck.
Early this month, the bolts were stressed, or placed under tension, to increase overall performance. Among 96 so far examined, 32 bolts were found broken about a week later.
Officials said it was too soon to know the cost of repairs, to identify where quality control failed or to place blame. But they cited the likely cause of the problem - defective steel contaminated by hydrogen during manufacturing. "Hydrogen embrittlement" can cause steel to crack or break.
Case Western Reserve University professor Arthur Hucklebridge, an expert on seismic issues in bridge construction, called the problem "extremely unusual" - more so because the bolts snapped after, rather than during, stressing.
Anziano told commissioners that a primary challenge to overcome is the lack of access to rods for two shear keys above the pier. In at least those cases, a work-around - possibly a collar attached to the base of the shear keys - will be used to replace or augment problem bolts.
"We have surmounted far greater engineering challenges than this one in getting this bridge constructed," said Steve Heminger, executive director of the Metropolitan Transportation Commission. "And I have no doubt that we will get through this one as well."
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.
In 2011 and 2012, a series of Bee articles described testing and record-keeping lapses for the foundation of the new span tower that raised doubts about its structural integrity. The problems were reviewed and dismissed by Caltrans, but an expert panel assembled by the Legislative Analyst's Office expects to report on its own investigation by June 30.
"If the safety of the bridge is involved, we will investigate fully," said Sen. Mark DeSaulnier, D-Concord, chairman of the California Senate Transportation and Housing Committee, regarding the most recent construction problem.
Call The Bee's Charles Piller, (916) 321-1113. Follow him on Twitter @cpiller.