California transportation officials said Friday that corrosion and cracking have been found on one of the steel anchor rods that secures the new suspension span tower for the San Francisco-Oakland Bay Bridge to its foundation – reinforcing critics’ concerns about the structure’s vulnerability in a major earthquake.
The bridge tower is secured by 424 massive anchor rods, each 25 feet long. Bridge officials reported last fall that about 95 percent of the rods had not been surrounded by grout, a cementlike paste that protects against corrosion. Some of the rods were not grouted at all. Construction spray or rainwater entered spaces around the rods, sparking concerns that corrosion and cracking might occur.
Rods on the eastern pier of the suspension span corroded under similar circumstances and snapped under tension in 2013, leading to a costly retrofit.
Caltrans’ chief engineer for the new span, Brian Maroney, called the tests “preliminary.” If some rods broke in a quake, he said, the tower still would stand but “might be perturbed, just a little bit.” Maroney indicated that by “perturbed,” he meant that the post-quake tower might lean to one side. There is no safety risk, he said.
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The tower rods would be impossible to replace and extremely difficult to retrofit. They are embedded in the steel and concrete cap at the top of the tower foundation. Only one was extracted and subjected to microscopic examination.
Tests showed that some of the rod’s outer layer of zinc – designed to protect the steel – had corroded and that tiny cracks had formed in the steel. Experts have warned that such cracks can expand over time and cause the rods to break under the extreme stress of a major temblor. Caltrans blamed the problem on contractor errors and vowed to protect the rods against additional corrosion.
Robert Bea, an engineering professor emeritus at UC Berkeley and an expert in risk assessment, called the test results worrisome. The rod problem, because it involves essential parts that cannot be replaced or repaired, represents “a deadly flaw” in the design of the troubled, $6.5 billion structure, he said.
“I’ve heard Caltrans incessantly say, ‘We understand this might be a problem, but the bridge is safe.’ When I hear that word ‘safe,’ I get very ill at ease,” Bea said. “They may believe it’s safe, but our job as engineers is to prove it.”
Caltrans’ next step, assuming that there are cracks in multiple anchor rods, Bea said, is to do a computer analysis of how the new span would behave in a major quake.
“Instead of trying to explain these things away,” Caltrans should explore solutions, Bea said, because engineers can nearly always work around even the most challenging problems.
Call The Bee’s Charles Piller, (916) 321-1113. Follow him on Twitter @cpiller.