The new eastern span of the San Francisco-Oakland Bay Bridge has more than 1,200 bolts made from galvanized steel that is virtually identical to a high-strength alloy that a nationwide group of transportation officials banned for use on bridges because the bolts can crack, the San Francisco Chronicle reported.
The bolts are used to anchor structures designed to keep the bridge stable in an earthquake, band the main cables together, hold the cables down at the top of the tower and bind them to the road decks.
Caltrans said last week that it was testing 192 bolts on the bridge that are similar to 32 galvanized bolts that cracked when workers tightened them in March.
The failed bolts were among 96 supplied in 2008 by Ohio-based Dyson Corp., the same firm that delivered the batch of 192 bolts two years later, The Chronicle said.
Documents examined by The Chronicle show that state has purchased 932 other fasteners for the bridge in the past five years that – like the failed bolts – were made of high-strength, galvanized steel.
“This is completely the wrong material for use in this application,” Charles McMahon, emeritus professor of materials science at the University of Pennsylvania, told The Chronicle. “I have devoted decades of my career to studying this. This steel is almost guaranteed to give you cracking under these conditions.”
The American Association of State Highway Transportation Officials – a national organization that sets standards for steel used in large highway structures – bans high-strength, galvanized bolts for bridges, The Chronicle said.
Last year, the Federal Highway Administration warned the state highway officials group about galvanizing such hardened steel for bridge use. Such bolts “are susceptible to possible stress corrosion cracking and embrittlement during galvanizing,” the federal agency said.
But Caltrans said in a statement to The Associated Press said that it used standards set by the American Society for Testing and Materials, an organization that, according to its website, develops and disseminates high-quality standards and technical information.
“The design team determined that in this application, American Society for Testing and Materials standards were appropriate. We ordered the steel consistent with those standards and in a way to guard against hydrogen embrittlement,” Caltrans Director Malcolm Dougherty said in the statement.
“In March, bolts broke at one location and we’re going to solve that problem. If that means replacing more rods, that’s what we’ll do. We’re taking a very thorough and methodical approach that is based on scientific evidence and rigorous testing,” the statement said.
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