Authorities overseeing construction of the Bay Bridge’s new eastern span said today that they think they know what caused numerous large anchor bolts on the span to fail but that they still haven’t decided on the best solution.
They told the Metropolitan Transportation Commission’s Bay Area Toll Authority today that they still don’t know whether the problem will force a delay in plans to open the new span in early September.
“Give us two weeks to give you an answer,” MTC Executive Director Steve Heminger said.
MTC and California Department of Transportation officials learned recently that about one-third of the 96 bolts that were installed on a pier just east of Yerba Buena Island had popped out several inches after they were tightened.
Those bolts, which were manufactured in Ohio in 2008, are located near where the new span’s self-anchored suspension span meets its skyway.
Caltrans Director Malcolm Dougherty said a detailed investigation has confirmed original suspicions that the bolts’ failure was due to hydrogen embrittlement, as excess hydrogen caused threaded areas in the bolts to become brittle and fracture under high tension.
Dougherty said the sources of the excess hydrogen may have been internal — such as an error during the production process — or external, such as exposure to fog and other weather conditions, or both.
Caltrans Executive Director Andre Boutros said transportation officials are looking at two possible approaches to the problem: building a steel collar in which two plates would be stacked or welded together, or building a steel saddle.
A contractor already has placed a steel order for both design options, Boutros said.
Heminger said the bolts made in 2008 definitely need to be replaced before the new span opens, but that “the hardest question” is whether to replace another batch of 192 bolts that was made in 2010.
He said none of those bolts have failed in tests over the past month, but that more testing will need to be done before they are considered safe.
Dougherty said the decision on the 2010 bolts will be a key factor in whether the new eastern span can open on time in September.
He said today, “We don’t know if we can count on the 2010 bolts.”
Heminger said there could be concern about stress corrosion in the 2010 bolts, but if that occurred, the problem would develop over a longer period of time than the hydrogen embrittlement problem in the 2008 bolts.
He said if that’s the case, it is possible that the new span could open with the 2010 bolts and they could be replaced gradually over a longer period of time.
Heminger told the commission that transportation officials won’t open the new span until it is ready, but that they feel time pressure because the current span is unsafe in the event of a major earthquake.
He said, “Those twin challenges keep our team working hard. Safety is not job one — it’s the only job we have.”
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