OAKLAND -- Caltrans' use of large galvanized steel fasteners on the Richmond-San Rafael bridge in 2001 led to engineers' choice to deploy the same specifications for the bolts that later snapped on the new Bay Bridge.
High-strength steel coated with zinc is susceptible to a well-known phenomenon where hydrogen atoms invade the metal's molecular structure and it becomes brittle and fractures. National standards caution engineers about its use and Caltrans' own bridge design manual prohibits it on ordinary spans.
But the state and private engineers designing the unique self-anchored suspension span for the Bay Bridge in 2003 believed the steel rod manufacturing modifications developed for the Richmond-San Rafael retrofit in 2001 would sufficiently reduce the risk of hydrogen embrittlement, according to dozens of project documents, emails and letters Caltrans released late Tuesday.
The change "does the trick for galvanizing high-strength rods," wrote Caltrans engineer Robert Kobal to his colleagues in April 2003.
Ten years later, that decision would prove costly in dollars, time and public confidence.
In early March, a third of the 96 high-strength threaded rods -- 3 inches in diameter and 17 to 24 feet long -- broke in key seismic stabilizers on the span after contractors tightened them down.
Engineers blame hydrogen embrittlement triggered by the combination of susceptible steel; the presence of hydrogen atoms trapped during galvanizing; and the heavy load on the fasteners.
Caltrans, Bay Area Toll Authority, the bridge contractor and the team of private engineering consultants hired to design the span are now scrambling to determine whether a proposed $5 million to $10 million repair job can be finished in time to open the bridge as scheduled.
They must also settle unanswered questions about the long-term integrity of the other 2,210 high-strength steel fasteners used on the bridge fabricated in the Midwest under identical specifications. Testing is under way but it could be weeks or months before engineers have the results.