Bridges of the twenty-first centuryWorries about safety of California bridges with eyebar design
Every so often the Bay Bridge closes because of widening eyebar crack; when the bridge opened seventy years ago, the design was considered safe, but structural engineers now say the eyebar design is an inherently unsafe; trouble is, dozens and dozens of California aging bridges use the flawed design
The major problem caused by a critical design flaw on the Bay Bridge were clear for residents of the area days of closures because of a cracked eyebar. What about other bridges in California of similar design? Federal law mandates inspections just every couple of years, but many ask whether, based on what has happened on the Bay Bridge, this is sufficient.
ABC7news’s Heather Ishimaru reports that structural engineers say that eyebars have flaws inherent in the way they were manufactured and yet they are still in use all over California on aging bridges in a time where infrastructure funding has been neglected for decades.
The cracked eyebar on the Bay Bridge is 70 years old. When new, it was considered the best in bridge design. Nevertheless, in 1967 that theory came crashing down along with the Silver Bridge, an eyebar suspension bridge, linking West Virginia and Ohio. The Silver Bridge collapsed on a cold December evening, killing forty-six people. The whole bridge came down after the initial failure of one eyebar.
“The belief at the time was that these were efficient and safe and perform well, but experience since that time has demonstrated that they don’t always perform as we originally intended,” says U.C. Berkeley engineer Jack Moehle.
The Silver Bridge collapse virtually ended the use of eyebars and lead to federally mandated bridge inspections every two years.
The old Carquinez Bridge was closed down for two years after the Silver Bridge collapse, because its design was so similar. The new Carquinez or Zampa Bridge has no eyebars in its design. Regardless, fifty-five California bridges built before 1967 are still in use, most of them are run by local agencies.
The state-run bridges with eyebars in the Bay Area include the Bay Bridge and the Richmond-San Rafael.
Caltrans says it would take more than one eyebar failure to bring down the Bay Bridge, but what about the Richmond Bridge? “There is redundancy in the that the load paths, or the way the weight is distributed, changes over time because they see so much rigorous use,” says Caltrans spokesperson Bart Ney.
“Given what’s happened recently with the Bay Bridge, I guess it wouldn’t hurt to go back and give it an inspection and maybe step up the inspection intervals,” says Moehle.
Caltrans is still deciding on a permanent repair to the cracked Bay Bridge eyebar. One option is replacing it with something else entirely.”It will be a structural steel member that doesn’t have the same issues as eyebars — probably a different geometry,” says Ney.
Ishimaru reports that replacing the cracked eyebar with something entirely new is still just one of many options being considered. Caltrans, of course, wants to emphasize that public safety is always its No.1 priority. There should soon be available more information on the state’s bridges in January. The state Senate will be holding hearings on the failure of the first Bay Bridge cracked eyebar repair.
