Decision on Bay Bridge opening date due soon, amid more bolt doubts
04/24/2013 12:13 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 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 new eastern span.
Doubts about 192 other anchor bolts that secure separate seismic equipment on the suspension span have prompted new and extensive tests that might result in the bolts' rejection. Officials also plan to announce that decision on 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 cautioned that officials need to finish the new span as soon as possible because the old bridge, currently in use, 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. Materials for each possible solution have been ordered from a nearby supplier.
The Bee reported last week that test data for some of the anchor bolts, produced in 2010, showed particular 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 for such problems, experts said.
In a detailed report provided Monday to the commission, retired materials engineer Yun Chung wrote that the bolts were vulnerable because their surfaces were too hard. He cited high readings for tensile strength as a key indicator.
"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 commission meeting that Chung's analysis was similar to what agency consultants have recently described. A report on Caltrans' findings could be released on May 8.
Tensile strength over 150,000 pounds per square inch, said Chung and other metallurgy experts, suggests greater susceptibility to hydrogen contamination. The 2010 samples tested as high as 165,000 pounds per square inch, and some 2008 samples showed readings well above 170,000.
Heminger told commissioners that if the 2010 bolts must be replaced, but their vulnerability to breakage does not seem imminent, Caltrans might wait until after the new bridge is placed into service.
The Bee also previously reported that some of samples for bolts produced in 2010 failed elongation tests, as did some samples from 2008. Caltrans said last week that the 2010 bolts passed tests because the agency average results across samples - some can fail if others exceed the standard. That approach was criticized as misguided 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 that the company subsequently improved its procedures and achieved a passing grade prior to manufacturing the bolts in question. According to internal Caltrans documents obtained by The Bee, Dyson parts of many kinds failed quality tests - a record inferior to other suspension span suppliers. Caltrans said that it would carefully monitor all Dyson parts installed in the new bridge.
Call The Bee's Charles Piller, (916) 321-1113. Follow him on Twitter @cpiller.
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