With six months left before the Labor Day opening of the new Bay Bridge span, Caltrans has already managed to break a significant portion of the most expensive public works project in California history. 32 of the 96 seismic stabilizing bolts on the bridge failed during a stress test meant to simulate the lateral motion of a large earthquake.
At the moment Caltrans says it is too soon to say what caused the bolts to fail, but they suspect it had something to do with "hydrogen embrittlement" — a fancy term for steel contaminated with hydrogen during manufacturing. The steel bridge deck was famously made in China and the devices the bolts fit into were made in Korea, but the bolts themselves were manufactured right here in the United States. It's like we had one job to do and we blew it.
The bolts in question are used throughout the bridge and fit into bearings and shear keys — two different devices that allow for a certain amount of side-to-side movement during an earthquake. All of the broken bolts appear to have been connected to the shear keys, although Caltrans workers are now questioning how sound those other devices are and will be inspecting a total of 288 bolts across the span. One seismic expert explained that the problem was "extremely unusual" because the bolts snapped some time after the stress test rather than during.
Project manager Tony Anziano said the problem should not delay the bridge opening, but "time is absolutely tight" for the fix, which is expected to take months to complete.
"We have surmounted far greater engineering challenges than this one in getting this bridge constructed," Metropolitan Transportation Commission executive director Steve Heminger told the Sacramento Bee. "And I have no doubt that we will get through this one as well."