4/25/2013 3:56:00 PM
NEWS BRIEF
Oakland Bay Bridge officials confirmed the cause of the 32 snapped anchor rods on the new $6.4 billion eastern span of the bridge.
“The failed rods suffered from hydrogen embrittlement,” Caltrans Director Malcolm Dougherty announced at an April 24 meeting of the Bay Area Toll Authority in Oakland.
FIN covered the meeting via an online audio feed.
The rods were from one of two distinct batches of bolts manufactured by Ohio-based Dyson Corporation.
One batch included a total of 96 rods manufactured and installed in 2008. The “failed bolts” came from that batch, which were embedded in concrete during construction.
A second batch of anchor rods, totaling 192, are through bolts manufactured in 2010 and installed in 2011. None of those bolts, which have been under load since April 9, have failed.
Failed bolts
Dougherty said lack of uniformity in the steel microstructure of the 2008 bolts increased susceptibility to hydrogen embrittlement.
Bridge officials have “substantially” expanded testing of the 2010 bolts to evaluate their disposition. Click here to see the official presentation.
Their investigation into the failure of the 2008 bolts and the conformity of the 2010 bolts includes analysis from a three-member expert panel currently evaluating both sets of bolts. The panel includes Canadian engineer Salim Brahimi, president and principal engineer at IBECA Technologies Corp. in Montreal, Canada. A member of ASTM since 1997, Brahimi works on several F16 subcommittees and is vice chairman of F16.02 on steel bolts, nuts, rivets and washers.
MTC Executive Director Steve Heminger conceded that Caltrans failed to provide adequate specifications to the manufacturer or mandate specific tests that would have revealed whether the bolts were susceptible to hydrogen embrittlement.
“These bolts were sort of bought out of the catalog instead of being tailor made,” Heminger stated. “The bolts are the dumb end of the operation. The seismic devices are the smart end.”
“You need something to hold them together. Frankly we would have used super glue if that had been appropriate.”
Two possible fixes
The bridge oroject team has narrowed response to two options: either a steel collar or steel saddle. Both options will achieve the design intent of this system.
The contractor already engaged in process, and has already steel orders for both options as well as lining up fabricator for both options. ©2013 GlobalFastenerNews.com
For an independent analysis of the Bay Bridge bolt failures, click here.
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