Stress Testing In San Francisco – Bolts Fail On The Bay Bridge


In a startling turn of events, it seems that a considerable 1,200 bolts, in total, might need to be replaced on the new eastern span of the Bay Bridge. Recently, there were 32 bolts that were found to be cracked and needed to be replaced immediately. However, the worst part of it all is that the 1,200 steel fasteners were discovered to be made of the same metal as the 32 cracked bolts. Fasteners are synonymous with rivets, like a blind rivet that you would see on an airplane wing. Someone clearly made a mistake when ordering their materials. So what does this mean for the bridge? Currently, state transportation officials are testing 192 bolts for possible future failure. If their results prove to be negative, then those 1,200 some-odd bolts will need immediate replacing.

The new Bay Bridge was scheduled to open before Labor Day 2013. The construction is being managed by the California Department of Transportation (Caltrans). Caltrans has been quiet as to whether or not these bolt problems will cause delays, but a recent article posted in SFist speculates that they might.

What Experts are Saying:

Retired Bechtel Metallurgist, Yun Chung, wrote up a massive 32-page report last week that criticized the Caltrans engineers, calling them “ignorant to the threat of hydrogen embrittlement.” Hydrogen embrittlement, for those not in the know, is “a process in which high strength metals, such as steel, become brittle and fracture due to hydrogen exposure.” Chung went on to explain that the type of steel that was used in the manufacturing of the bolt was much harder on the outside than the required specifications laid out by Caltrans in their designs. According to Chung, the engineers were only focused on hydrogen exposure during the actual manufacturing of the parts in question, and not on exposure to the elements, which Chung believes to have caused the bolts to become brittle and snap.

Speculation on the Mistake:

This entire fiasco seems like it could have been easily avoided. It causes you to wonder just what the Department of Transportation was thinking when planning the eastern span. They should have taken the elements into consideration! Just look at the Statue of Liberty, for example. Constructed in 1886, it stood beautifully in bronze copper. Within the next ten years, Lady Liberty turned gradually into the lurid green we see today. While not causing a danger to tourists, it stands as a reminder that weather affects metal when exposed to the elements. Metallurgy is a pretty basic factor to consider when planning out a new structure. Common questions include: what is this metal made of? How is it affected by uncontrollable forces? What can we do to ensure there are as little problems as possible?

It is fortunate, however, that this discovery was made before the bridge was opened to the public. Imagine the consequences of such a grievous mistake! This just goes to show you the importance of safety testing the bridges, as faulty parts like this can be found and replaced before any lives are lost. All in all, it is better to err on the side of caution when it comes to large structures like bridges.

Dusty Hunter is a vegetarian carpenter. He writes about the things he loves.

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