Brian Maroney, chief engineer for the new San Francisco-Oakland Bay Bridge, said Thursday that even if all the anchor rods that secure the suspension-span tower to its foundation were missing, the bridge would barely budge in a major earthquake.
He was responding to recent findings of tiny cracks found in a rod extracted from the bridge by the California Department of Transportation. Independent experts have cautioned that the structure could prove vulnerable in a temblor.
At worst, the tower would lean slightly, but “it’s not going to be the leaning tower of Pisa,” Maroney told the Toll Bridge Program Oversight Committee, which supervises construction and spending for the span. The $6.5 billion project has been plagued by construction lapses.
The tower was secured by 424 rods, each 25 feet long. During construction, the builder failed to seal sleeves that hold the rods, and water collected in them. Corrosion – caused by the water – and stress can cause cracking.
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Rods on another portion of the span snapped under similar circumstances in 2013, necessitating a costly retrofit.
Andrew Fremier, deputy executive director of the Metropolitan Transportation Commission, said in an interview that officials believe all the rods were contaminated by water. In 151 cases, they were not fully surrounded by grout – a cementlike protective paste. Some were not grouted at all. Standing water was found years after it entered the sleeves.
Caltrans recently used high-strength water jets to drill holes in the grout for all 424 rods to assess their condition. Maroney recommended that the rods remain ungrouted but that Caltrans dry the holes and monitor the rods over the bridge’s 150-year service life.
No matter what the condition of the rods, he said, the bridge would only lift a fraction of an inch in a major quake, and the span’s roadway would move just slightly.
Oversight committee Chairman Steve Heminger asked if such assurances mean that most of the rods were not needed. Maroney said they were for an extra measure of safety.
Some quality assurance documents associated with the rods could not be located. The committee approved further research to examine and respond to the problem.
Between 2011 and 2012, some of the rods were placed under an unknown amount of extra stress when the tower was pulled slightly to one side to accommodate construction.
“If it’s stress corrosion cracking, you need to sustain the load for a long time. One year is a long time,” Maroney said. He conceded that he does not know if some rods might already have snapped.
Robert Bea, engineering professor emeritus at UC Berkeley, cautioned in February against declaring the bridge safe and “trying to explain these things away” without adequate research – particularly when the rods would be difficult to retrofit and impossible to replace.
Call The Bee’s Charles Piller, (916) 321-1113. Follow him on Twitter @cpiller.