Caltrans plans to have repair timetable for new Bay Bridge span on May 8
04/24/2013 5:56 PM
04/12/2014 7:26 PM
Transportation officials said Wednesday that they hope to announce on May 8 the cost and timing estimates for retrofitting and repairing the new San Francisco-Oakland Bay Bridge.
Officials are working on an engineering fix to hold down two shear keys – a type of seismic safety device – originally secured by 96 large anchor bolts, some of which broke in March.
Caltrans has said that the timing required for a solution to that problem has jeopardized the projected Sept. 3 opening date for the new eastern span.
Doubts about 192 other anchor bolts that secure separate seismic equipment on the suspension span have prompted new tests that might result in the bolts' rejection. Officials also plan to announce that decision May 8.
Steve Heminger, executive director of the Metropolitan Transportation Commission, promised commissioners meeting in Oakland that "we will open the new east span only when it's ready and not a day sooner."
But he cautioned that the new span must open as soon as possible because the old bridge would be unsafe in a major quake.
"Safety is not job one," Heminger said. "It's the only job we've got."
Two design options – steel collars placed over the two shear keys, and steel saddles that surround each device and a portion of the eastern pier of the suspension span – are being considered.
The Bee reported last week that test data for some of the anchor bolts, produced in 2010, showed susceptibility to becoming brittle when contaminated with hydrogen – the case with the bolts that snapped, which were manufactured in 2008. Tensile strength tests showed that samples from both sets of bolts tested above levels that should have raised red flags, experts said.
In a detailed report provided Monday to the commission, retired materials engineer Yun Chung wrote the bolts were vulnerable because their surfaces were too hard. He cited high readings for tensile strength and measurements of hardness.
"Caltrans has been oblivious to the possibility of these anchor rod failures due to (hydrogen embrittlement) during the 150-year design life of the new bridge," Chung wrote. The bolts were at risk, he said, "because they were too strong or too hard at the surface. And the blame goes to Caltrans' specifications" for tensile strength and other characteristics.
Heminger and Caltrans Director Malcolm Dougherty said at the meeting that Chung's analysis was similar to what agency consultants have recently described.
Heminger called the decision whether to replace the bolts produced in 2010 "a difficult call," in part because after 15 to 25 days of tension, none has failed.
"We need to know more," he said. "We need to know why they have not failed" to restore full confidence in the parts.
A new battery of destructive tests – including microscopic and tensile examinations – will be conducted on at least six of the 2010 bolts removed from the structure.
The 2008 bolts were problematic, in part, due to their location inside the eastern pier, where access is difficult and the corrosive effects of trapped water might have played a role in their failure.
The Bee also previously reported that some samples for bolts produced in 2010 failed elongation tests, as did some samples from 2008.
Caltrans said last week that the 2010 bolts passed elongation tests because the agency averaged results – it allowed some samples to fail if offset by samples that exceeded the standard. That approach was criticized by UC Berkeley engineering professor Thomas Devine.
Caltrans audits in 2007 of the bolt supplier, Ohio-based Dyson Corp., showed substandard results. On Wednesday, Dougherty said the company subsequently improved its procedures, achieving a passing grade prior to manufacturing the bolts in question.
According to Caltrans documents obtained by The Bee, Dyson parts of many kinds failed quality tests – a record inferior to other suppliers.
Heminger said testing records for other Dyson parts will be examined and a report made public. Caltrans has been monitoring Dyson parts installed in the new bridge, and so far no problems beyond the broken anchor bolts have been observed.
Call The Bee's Charles Piller, (916) 321-1113. Follow him on Twitter @cpiller.
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