Assessments by the California Department of Transportation and its expert advisers – that the bridge is safe and durable – were based on “erroneous and misleading” evidence, according to the report.
An independent report released today sharply criticized official tests of high-strength steel rods that secure the new San Francisco-Oakland Bay Bridge, concluding the analysis was flawed and that some bridge parts should be replaced.
The report said assessments by the California Department of Transportation and its expert advisers – that the bridge is safe and durable – were based on “unscientific” and “erroneous and misleading” evidence.
The critique was authored by Yun Chung, a retired metallurgical engineer who has studied the matter since some threaded rods on the eastern pier of the span snapped in March 2013. Chung said Caltrans’ test protocols, data analysis and conclusions about the reliability of the suspension span “could not be supported.”
Chung proposed replacing most of the suspect bolts and rods with others whose qualities remove vulnerability to cracking.
Caltrans had concluded in a report issued in September that, based on multimillion-dollar tests, the suspect anchor rods can be left in place.
“Based on the findings of this investigation, nothing further is needed to ensure the integrity of the (suspect) rods,” other than additional protections for rods on the eastern pier of the span, and usual maintenance, according to the Caltrans’ report.
“We appreciate public feedback, and will review the comments,” Caltrans spokeswoman Tamie McGowen said in a written statement about Chung’s report. Caltrans’ testing report, prepared by “some of the top experts in the country in materials engineering and corrosion science,” she said, “is not final and there is still ongoing testing activity.”
The Toll Bridge Program Oversight Committee must approve the report. It has indicated general agreement with Caltrans’ results but has yet to sign off.
Seven experts from academia and industry who are not affiliated with Caltrans reviewed Chung’s report and their comments were incorporated, he said. Several of the reviewers praised Chung’s 60-page report and criticized Caltrans’ work.
In an interview, Charles J. McMahon Jr., professor emeritus of materials science and engineering at the University of Pennsylvania, called Caltrans’ testing “so defective that it’s useless.”
McMahon, like Chung, said Caltrans tests couldn’t remove the main problem: The bridge uses the wrong material – very hard, high-strength steel rods – for stressed service in a marine environment. “That practically guarantees that hydrogen-induced cracking will occur at some point,” McMahon said.
Another reviewer, Robert Bea, professor emeritus of engineering at UC Berkeley, in an email to Chung, called the findings, conclusions, and recommendations in Chung’s report “appropriately reasoned.”
Chung, who trained at UC Berkeley, formerly managed the Bechtel Corp. San Francisco welding and metallurgy lab. He later performed failure analysis at Hayward-based Anamet Inc., a materials engineering and testing firm.
After 32 of 96 rods attaching seismic equipment to the eastern pier broke in 2013, Caltrans concluded they became brittle after hydrogen atoms entered the steel during manufacturing, including during galvanization with molten zinc to protect against corrosion. The technique generally is regarded as ill-advised for the very hard, large, high-strength rods and bolts used in the project. Construction problems also exposed the rods to standing water, off and on, for about five years – a factor that Chung previously blamed as a principal reason for their cracking.
A “saddle” retrofit was installed to perform the function of the broken rods. The $6.4 billion span opened the following September.
Caltrans’ report said tests “of unprecedented breadth and depth” found that the remaining steel rods pose no threat to public safety or to the durability of the new span. The state report described tests designed to determine whether any other steel rods on the new span might be susceptible to hydrogen-related brittleness.
The Caltrans tests included mimicking the marine environment by soaking sample rods in saltwater for weeks to test their strength under increasing stress. The rods broke only after the stress applied greatly exceeded that expected to be faced by the new span, according to Caltrans test reports.
Caltrans noted that all anchor rods in use will be protected from corrosion and in many cases are tightened to tension levels too low to make them vulnerable to hydrogen-related cracking.
Caltrans hired respected materials experts to assist with testing, including Herbert E. Townsend, a retired researcher for Bethlehem Steel Corp.; Karl H. Frank, professor emeritus at the University of Texas at Austin; and Louis Raymond, an expert in how metals fracture who has extensive aerospace experience. Among others, they were involved in test design and analysis.
Chung said Caltrans nevertheless failed to detect or address key factors that render the tests invalid.
The maximum anticipated tension levels that the threaded rods will experience on the new span are far higher than what Caltrans assumed and tested for. This is because stress is highly concentrated in the roots of the threads where engaged by nuts, Chung said.
Chung’s report reiterated his longstanding concerns that many of the rods are harder internally than at their edges. That creates additional uncertainty about their susceptibility to cracking, according to Chung.
He argued that Caltrans should replace hundreds of high-strength anchor rods and bolts with others that are known to be highly resistant to that problem, as is normally done on bridges exposed to corrosion from rain, fog and salt.
McMahon concurred that in general, the types of rods that Caltrans used are too vulnerable. In an email to Chung, which McMahon provided to The Bee, he said “any such rods in the bridge should be replaced. Period.”
Anchor rods at the tower base, which Caltrans recently acknowledged had been contaminated with water due to construction errors, would be difficult or impossible to replace, as they are embedded within a concrete and steel foundation. Chung suggested close monitoring and a risk analysis for those rods.
Officials are still evaluating the tower-rod problem but have said they do not consider hydrogen-related cracking to be a risk because those rods are under relatively low tension.
McMahon said he had been approached by bridge officials last year to be a testing consultant, but he declined.
“I sensed that from the stuff they put together that they were (forming) a group of experts to bless what they were doing,” he said.
Another expert in materials science, Russell D. Kane, president of iCorrosion LLC in Houston, reviewed Chung’s report and called it “credible.”
“I was very impressed with the thoroughness and the open-mindedness” of Chung’s report, and with the detailed assessment of Caltrans’ work, Kane said in an interview.
“You have to err on the conservative side, rather than try to dance on the head of a pin to make the data work,” he said. “I’ve gotten the feeling that (Caltrans has done) a lot of head-of-the-pin dancing here.”
©2014 The Sacramento Bee (Sacramento, Calif.)