Testing underway on new Bay Bridge bolts

August 2, 2013 8:34:36 PM PDT
Another round of testing is underway for those giant bolts on the new Bay Bridge, but this is a batch of bolts that hasn't snapped. The question is whether the results of these tests could further delay the bridge opening?

The answer is no, but these tests were prompted by the failure of the first set of bolts. The goal now is to make sure all the bolts are safe for many years to come and also to restore public confidence in the integrity of the entire structure.

The giant chambers the huge bolts are encased in are designed to replicate the conditions similar bolts face out on the new eastern span of the Bay Bridge.

"Remember, we need three things. We need high stress, we need a susceptible material and we need hydrogen," Bill Casey said. "What we're trying to do is accelerate the corrosion process. Create a corrosion cell, force hydrogen into the bar, put it under load and slowly step it up over time."

The hydrogen comes in the form of salt water. Instead of it and the other influences impacting the bolt over a span of decades, the chambers condense that time period into less than a month.

Asked what happens if a bolt fails, construction engineer Bob Brignano said, "We are taking these to failure. It's just what point is that failure and determining what that failure point is."

Whatever happens to these bolts during these tests, it won't delay the opening of the new Bay Bridge any further. They are what Caltrans has been calling the "2010 bolts," the ones made two years after the infamous batch that snapped.

Those, the "2008 bolts" are embedded in concrete so engineers have come up with an elaborate saddle system to reinforce them in case of an earthquake. That retrofit is being fabricated at Mare Island and its installation is crucial to the opening of the new span.

The "2010 bolts" are accessible and could be replaced well after the bridge opens if they show vulnerabilities in these tests.

"That data will tell us what needs to be done with these bolts years down the line, decades down the line, whether they can stay in place, whether they should be removed and replaced with new bolts, whether we need to dehumidify the area that they're in, or just maybe lower the tension a bit," said Caltrans Bridge Spokesman Andrew Gordon.

As it is now, the opening of the new bridge is now set for some time after the saddle retrofit is in place. That is expected in mid-December.

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