Monday, May 6, 2013

Inappropriate Galvanizing Likely Led To Bay Bridge Bolt Failures

Potential significant delays in the scheduled Labor Day opening of the replacement for the San Francisco to Oakland Bay Bridge - replacing the span which failed, killing one motorist, 23 years ago during the magnitude 7.1 Loma Prieta earthquake -  could be the result of a flawed decision by CALTRANS engineers to call for galvanizing of the 288 three inch diameter high strength A354 BD steel anchor bolts connecting the bridge deck with its shear keys, bearings and columns, according to preliminary information regarding a soon to be released failure analysis of the 96 bolts produced for the project in 2008. An additional 192 bolts of the same type made in 2010 are also under review.

ASTM International has warned for decades against galvanizing A354 BD grade high strength steel fasteners, concluding that "research on bolts of similar material and manufacture indicates that hydrogen stress cracking or stress cracking corrosion may occur on hot dip galvanized Grade BD bolts." One bolt maker - Portland Bolt and Manufacturing - actually declined to submit a bid on the Bay Bridge project because of the CALTRANS specification calling for galvanized BD grade bolts. According to Dave McKinnon, Portland Bolt's quality assurance director, "We won't galvanize A354 BD bolts for any reason. We've chosen to take ASTM's warning as more of an absolute." McKinnon is a member of ASTM's fastener standards committee.

Galvanizing, a relatively cheap and long lasting anti-corrosive treatment for steel, is prohibited on BD grade bolts by CALTRANS' own bridge design manual. The CALTRANS engineers responsible for the galvanizing specification on the Bay Bridge have not yet explained why they elected to go against the prohibition of their own procedures in designing the new Bay Bridge. Thirty two of the 96 bolts produced for the project in 2008 - each 17 to 24 feet long - snapped apart while iron workers were tightening them during construction last March. Intensive testing of the 192 fasteners from the same supplier produced in 2010 is also underway.

A report expected to be released Wednesday, May 8, 2013, should identify the cost, methodology and schedule for repair of the bolt failures, the decision whether to replace the 192 galvanized bolts produced in 2010, and any change in the scheduled opening of Bay Bridge. The incidence of failure by one in every three of the galvanized bolts produced in 2008 has weakened public confidence in the often touted earthquake stability of the new bridge structure.

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