California Department of Transportation officials acknowledged Wednesday, for the first time, the validity of some concerns raised by critics of the department’s evaluation of broken and suspect anchor bolts and rods on the new San Francisco-Oakland Bay Bridge.
At a technical briefing at the bridge offices in Oakland, Caltrans engineers said that ongoing tests looked promising, but they would address some of the outside objections as research continues on the 2,306 parts that secure the span’s main cable and tower.
The briefing was held to provide details on testing and address doubts raised by two local metallurgists about an official report on the rod problem. Retired Bechtel Corp. engineer Yun Chung and Lisa K. Thomas, a materials engineer at Berkeley Research Company, a consulting and test lab, analyzed transportation officials’ approach to evaluating the high-strength anchor rods for the tower and main cable of the suspension span. Their concerns were first detailed in December by The Sacramento Bee.
Steve Heminger, executive director of the Metropolitan Transportation Commission, headed the committee that produced the report. Last month he called their complaints “inconsequential” and “unsupported assertions.”
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But at the briefing Wednesday, Caltrans Director Malcolm Dougherty said the testing is about half done, and that his department remains open to new ideas before deciding if any rods and bolts must be replaced or other changes made. Those decisions are expected by this summer.
“What else do we need to take into consideration before that final decision is made?” he said.
The Chung-Thomas critique, peer reviewed by leading engineers, concluded that the Toll Bridge Program Oversight Committee, which supervises the new span, overemphasized manufacturing flaws as the cause of 32 massive rods snapping last March. Chung and Thomas blamed the failure primarily on corrosion that occurred after construction errors exposed the bottom of the rods – where all the breaks occurred – to water off and on for five years.
The oversight group’s conclusion glossed over the odds of 1 in 4 billion against all the rods failing in the same location without the environmental corrosion, Chung said in prepared remarks. The mistake has significant implications on plans for evaluating other suspect rods, he said.
Chung compared the oversight group’s analysis to a postmortem medical report after 32 people died from snakebites. It was as if the death certificate failed to mention that all the bites were “in the ankles, not in the neck or arms,” Chung said.
Citing numerous technical errors and misconceptions in the oversight report, he called it “unintelligible” and “not acceptable as an engineering report and as a public document I am ashamed of the state officials who let it out.”
Chung and Thomas asked for samples of the suspect anchor rods to conduct independent testing.
Thomas said that scientists from the National Institute of Standards and Technology also have offered to conduct neutron tomography and gamma ray activation tests that might determine the presence of hydrogen in the broken and suspect parts. Such data could offer new insights on the vulnerability of the rods to future cracking. She urged Caltrans to take the agency up on the offer.
Moisture in the bay’s marine environment could corrode other suspect anchor rods. Chung and Thomas questioned the adequacy of Caltrans’ efforts to dehumidify chambers in which some critical rods are housed to prevent that possibility. Caltrans has defended those protections, despite recent concerns raised by leaks of rainwater inside most of the suspension span roadway through 800 bolt holes.
Ongoing tests to mimic long-term environmental corrosion also suggest that the rods will be reliable for the span’s 150-year service life, according to bridge spokesman Andrew Gordon. Those tests involve soaking large anchor rods in salt water, then stressing them to the breaking point.
Caltrans corrosion consultant Herbert Townsend Jr., a noted expert in stress corrosion cracking, called these full-scale tests unprecedented, and a “truly a remarkable achievement.” The first of four phases of tests showed that the rods did not crack until well beyond the stress level they would be exposed to in normal use on the bridge. But he acknowledged that considerable uncertainty – and much additional testing – remains.
Chung said in his prepared remarks that those “Townsend Tests” could prompt a false sense of security, because they don’t predict the long-term performance of rods that secure the suspension span’s main cable and support its tower.
He also cited unusual, poorly understood hardness qualities, not raised in the oversight report, for many anchor rods that raise questions about their vulnerability to brittleness.
The rods and bolts in question generally are harder at the edges than in the interior of the parts. But many of the rods in question tested as harder internally – a factor that Chung and Thomas believe could increase brittleness and requires new research.
Caltrans materials engineer Bahjat Dager said that the department had begun to explore Chung’s question, but so far had no explanation for the strange hardness profile.
Chung noted that threads on rods that secure the main cable at its eastern anchorage were fabricated with a “cold roll” process that increases hardness in the threaded areas compared to machine-cut threads.
Harder areas can be more susceptible to brittleness caused by hydrogen introduced into the steel during manufacturing or by environmental corrosion.
“To guarantee the 150-year life of this bridge, Caltrans engineers need to know all there is to know about the properties of these anchor rods, to the intimate details,” Chung said.
Karl Frank, a Caltrans consultant and professor emeritus of engineering at the University of Texas, told Chung and Thomas that extensive tests on the thread issues are in progress.
“Don’t think that we are ignoring these issues,” he said. “We are thinking about the same things you are We want to give good answers. We want a safe bridge.”