Engineers Zero in on Bay Bridge Broken Bolt Solutions
Engineers have yet to settle on a fix for the more than 30 bolts they found had cracked on the new eastern span of the Bay Bridge, but there are two likely fixes engineers could implement, said Steve Heminger, the executive director of Metropolitan Transportation Commission, on Forum Thursday morning.
One is to replace all the bolts. Metal testing suggests hydrogen got in during the galvanizing process, which makes the steel brittle.
The other is what Heminger calls a “belt and suspenders” solution: The bolts anchor earthquake-stability structures called bearings and shear keys, which prevent the bridge from moving up and down or side to side in an earthquake. Think of the bolts as the belt. In this case, the belt is too loose to hold the pants in the right place. Engineers could add collars around the bearings and shear keys for extra support – like adding suspenders to back up the belt.
But until the CalTrans investigation is complete, they cannot decide on a course of action, he said.
Either way, Heminger said, the cost will be minimal.
“I think the cost will end up being a rounding error in terms of this project,” he said. “We’re talking about a $6 billion bridge, and I can’t conceive of a solution that’s even going to cost a fraction of that amount.
The broken bolts will likely not delay the bridge opening on Labor Day, according to Heminger.
“This problem is obviously a significant one, but we do think it’s manageable,” he said. “One of the ironies here is that we have surmounted far greater engineering problems in building this bridge than bad bolts.”
On Wednesday, an MTC spokesman announced the discovery of the broken bolts, but engineers made the discovery several weeks ago after noticing the nuts on the ends of the bolts had come loose.
Members of the public have raised safety concerns over the new span of the bridge, especially after the discovery of the broken bolts.
Heminger said he recognizes the public’s concern, and he said that they won’t open the bridge until it’s ready. But the current bridge is a much more serious risk, he emphasized.
“The bridge we’re driving across today is not safe. We are certain of that,” Heminger said. “So we are certainly aiming to open the most state-of-the-art seismic bridge that we can construct. But we have to remember the one we’re driving on today is the reason we’re trying to open the new one on Labor Day weekend.”
Listen to KQED’s Joshua Johnson interview Heminger on Forum:
More on the broken bolts: