The anchor rods that hold in place strands of the main cable of the $6.5 billion San Francisco-Oakland Bay Bridge have a new problem: They are skewed off-center inside holes of the steel plate to which they are secured.
Among the 274 rods in anchorage chambers at the eastern end of the suspension span, 205 are less than the required 10 millimeters from the inner surface of the holes through which they pass, according bridge authorities.
In an earthquake, the rods – essential to the span’s structural stability – could be damaged by friction or collision with the plates, said Andrew B. Fremier, deputy executive director of the Metropolitan Transportation Commission, who revealed the problem at a meeting of the Bay Area Toll Authority on Tuesday.
Marwan Nader, a lead designer for the bridge with TY Lin International, and Bill Casey, the California Department of Transportation resident engineer for the suspension span, did not respond to requests for comment. It’s not clear how long authorities have known about the problem, but it did not appear on a list of ongoing maintenance concerns released by Caltrans last week.
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Fremier said in an interview that officials viewed the problem as important but not urgent. The rods might have to be pushed into a more central position – or the holes might have to be enlarged.
The latter approach could prove difficult, because the rods hold up the main cable and cannot easily be removed. It’s also unclear how the thick steel plate could be cut or bored inside the tightly confined chambers, said Arthur Hucklebridge, an emeritus engineering professor at Case Western Reserve University and expert in bridge engineering.
Hucklebridge said that such rod misalignments – perhaps the result of a fabrication or construction error – are not uncommon, and are accepted within certain limits. He said the decision to address the problem, if it’s the only issue of concern, suggests a relatively extreme situation.
The issue “has the potential for extending the contractor’s time on the project,” Fremier said. “Obviously anything that extends the time has a cost associated with it.” He could not provide a cost estimate, but said he expects repairs to last into this fall.
The misalignments added to concerns reported by The Sacramento Bee last month that many of the same anchor rods have rusted from exposure to rain and salty bay mist. The chambers that house them have not yet been sealed or properly dehumidified – conditions than can that jeopardize the long-term ability of the rods to secure the main cable. The strands of the cable also show rust, according to independent laboratory testing of residue samples collected by The Bee.
San Francisco supervisor and Toll Authority commissioner David Campos said that the rust issue will be examined by experts from the International Bridge, Tunnel and Turnpike Association, a global organization for owners of toll roads and bridges. They will review all ongoing maintenance concerns for the new span.