San Francisco News Blog

Mark Ketchum, one of the Structural Engineering Association of Northern California's designated experts on bridge design and failure, immediately likened yesterday's rupture to the failure of the eyebars on the 1927 Carquinez Bridge in the early 1970s. Like the Bay Bridge, that Carquinez span was an aging structure nearing the end of its useful life. But that's where the comparisons end.

Because the Crockett-to-Vallejo traffic is not on par with the East Bay-city commute, and also because the 1958 Carquinez span stood mere yards away and could easily be made to handle the traffic load, engineers actually undertook a lengthy study on whether to retrofit or replace the '27 bridge. They opted for the former and the old bridge served until the completion of the third Carquinez Bridge -- which Ketchum helped design -- in 2003 (the '27 span was dismantled in '07).

Obviously, those fixing the Bay Bridge don't have the same luxuries as their forbears who took months making the fix. Time is of the essence. And Ketchum adds that episodes like yesterday's show why it's a good thing that the eastern span of the Bay Bridge is on its way out.

When the third Carquinez span opened in 2003, it was cause for celebration

​While conceding that something obviously went very wrong with the Labor Day fix, "this is what happens when you try to keep up aging infrastructure from a different era of engineering to modern standards ... this shows why it was a good decision to replace the bridge rather than retrofit." After a while, he adds, putting work into an existing piece of infrastructure is less safe or economical than replacing it altogether. "It's just like buying a new car."

For anyone worried about the bridge collapsing altogether, Ketchum puts it thusly: Don't.

"We are a long, long way from any sort of major failure."

UPDATE, 12:22 P.M.: Ketchum just finished a long conference call with fellow members of the Structural Engineering Association of Northern California to figure out "what to say when you don't really know what's going on.

"But, he continues," I think what we can say is this: The temporary repairs done over Labor Day weekend obviously weren't intended to work this way. It's going to take a pretty good forensic investigation, that Caltrans can do themselves, to determine if this is a design issue, a fabrication issue, an installation issue or weather related or anything else."

Ketchum notes that "this was not a permanent repair, it did not need to last 70 years. It only needed to last five. It is not as robust as a permanent repair and who knows why it went wrong? I don't."

Photo of 1927 span   |   Wikimedia commons

Photo of 2003 span   |   State of California