What's Wrong with the San Francisco Bay Bridge?
By Charles Piller
Yun Chung, a retired engineer and metallurgist, read the official report explaining why massive, high-strength steel rods on the new San Francisco-Oakland Bay Bridge broke last March and was stunned _ then alarmed.
At first glance, Chung said about the July report, he saw obvious errors _ some typographical, others that confused basic terminology. Digging deeper, he discovered more important problems. He concluded that the analysis defied metallurgical science and common sense.
"I think it's very shameful that in this public document, this important (oversight) report, there are so many errors. (I have) a sense of outrage," Chung said in an interview last week.
Diverting attention from caring for his disabled wife, Chung, 81, said he spent hundreds of hours reviewing the report, consulting the technical literature and writing _ with another engineer _ a 105-page rebuttal. Chung, who had worked for Bechtel Corp., and Lisa K. Thomas, a materials engineer at Berkeley Research Company, a consulting and test lab, recently prepared an 18-page supplement to the report after a request from The Sacramento Bee to further detail their concerns.
Their unsolicited peer-reviewed report, which the two engineers completed in October, has gained traction among eminent engineers and a key elected official, and has begun to garner attention from bridge authorities.
The often-scathing critique disputes official assurances about the reliability of hundreds of high-strength steel rods that support the new San Francisco-Oakland Bay Bridge.
The two engineers challenged basic assumptions about why 32 rods that secured seismic gear on the eastern pier of the new suspension span broke in March.
Chung and Thomas wrote that hundreds of rods that attach the main suspension cable to its eastern anchorage and affix the tower to its foundation appear vulnerable _ not just the ones that broke. They called those rods "fracture critical."
"It means that their failures can bring down the entire (suspension) bridge," they said.
That does not mean drivers now using the bridge should fear its failure. After years of delays, construction problems and billions of dollars in cost overruns, the new Bay Bridge opened Labor Day weekend. But as traffic moves across the still-uncompleted span, questions about reliability and durability persist.
The engineers said they believe that the California Department of Transportation and other authorities responsible for the construction and maintenance of the $6.4 billion structure should be aware of potential problems and rectify them.
Chung said that some rods could pose long-term risks. "I want Caltrans to have the right understanding of the problem," he said, "Then they can have the right corrective actions."
Sen. Mark DeSaulnier, D-Concord, chairman of the Transportation and Housing Committee, is conducting hearings about management and construction lapses involving the span. He said the report by Chung and Thomas increases the urgency for a full independent review of the rods and other construction concerns. As part of his committee's work, DeSaulnier plans to ask University of California experts to examine the new assessment. "We're going to pursue it. It'll be part of our overall report," he said.
Also at DeSaulnier's direction, an independent expert panel coordinated by the Legislative Analyst's Office is conducting a separate review of construction problems on the bridge, including the anchor rods and suspect concrete in the tower foundation. Chung also sent the report to Steve Heminger, executive director of the Bay Area Toll Authority and chairman of the bridge oversight committee. Heminger said he was reviewing it with Caltrans officials and eventually would release a public response.
Chung was no newcomer to the issue. He became concerned last spring when he heard transportation officials make public statements that he considered false or misleading. Chung wrote a shorter technical analysis in April, which was discussed among elected officials and the media. He said it never prompted much of a dialog with those responsible for the bridge.
Trained at the University of California, Berkeley, Chung worked as a materials engineering specialist at Bechtel Corp. for 23 years and managed the company's San Francisco welding and metallurgy lab. He later served as a failure analysis and laboratory consultant at Hayward based Anamet Inc., a materials engineering and testing firm. He enlisted Thomas, who had worked with him at Anamet, to help.
The July analysis of the rods was written by the Toll Bridge Program Oversight Committee. That group comprises the chief executives of Caltrans, the California Transportation Commission and the Bay Area Toll Authority. It oversees construction of the new bridge.
After the rods broke in March, the oversight group commissioned a review from metallurgists hired by Caltrans and the bridge builders. Based on the consultants' work, the July oversight document largely concluded that the rods became brittle because hydrogen atoms entered the steel during manufacturing. The oversight group said it would be safe to open the new span after completion of a "saddle" retrofit intended to perform the function of the broken rods.
Some other anchor rods are to be substituted, but most were deemed adequate with monitoring, pending the results of a few new tests. Tension might be reduced for some rods to minimize the prospect of future cracking.
The bridge opened before the saddles were completed because builders installed a second retrofit _ steel shims _ as a temporary replacement for seismic equipment. The saddles will be done next month, according to bridge officials.
Out of concern for public safety, Chung worked with Thomas for more than three months to complete a detailed examination of the technical merits of the official oversight report. Errors and misinterpretation of data led to dubious conclusions about how to test and protect other vulnerable rods, the engineers said.
"(The oversight group and) Caltrans are not cognizant of metallurgical problems unique to these anchor rods," Chung and Thomas wrote. They called for changes in testing and remediation, "to provide valid assurance that these anchor rods will not fail."
Their findings were taken seriously by peer reviewers. Robert Bea, emeritus professor of civil and environmental engineering at UC Berkeley, Patrick Pizzo, emeritus professor of materials engineering at San Jose State University, and three other experts concurred with the report's recommendations.
Pizzo called the Chung and Thomas report "a critical look that should stimulate a conversation from the people directly involved in the project."
The broken rods were among several Bay Bridge construction matters that received scrutiny. The oversight committee report said the parties responsible for the rod problems were Caltrans, bridge designers T.Y. Lin International and Moffatt & Nichol, as well as bridge builders American Bridge Co. and Fluor Corp.
The oversight committee concluded that the rods became vulnerable when manufactured, including their galvanization with molten zinc to protect against corrosion. That technique can allow hydrogen atoms to enter the steel, causing brittleness in the hard, large, high-strength rods used in much of the new span. Construction delays exposed portions of the bolts at the east pier to standing water for about five years, off and on. That could have worsened the problem, oversight officials said.
Chung said he couldn't understand how the oversight group, its consultants, and even a review team from the Federal Highway Administration missed such an obvious conclusion: Over five years, water corroded the bottoms of the rods _ where all 32 breaks occurred. That was the primary reason they snapped when tightened. Corrosion introduced too much hydrogen into the steel at those locations.
Underplaying the environmental cause for the breaks _ "the most fundamental error in the (oversight) report" _ Chung and Thomas wrote, led to apparent complacency among oversight officials about future corrosion from the bay's marine conditions.
As a precaution against corrosion, giant rods on the suspension span's eastern anchorage and others at the top and base of the tower "are housed inside a watertight, dehumidified chamber so moisture is not readily present," according to the oversight group's report.
Chung and Thomas said that in the bay's marine air, the chambers must be more than watertight _ they should be airtight to prevent corrosion. Pizzo agreed that airtight chambers would be necessary.
Chung and Thomas cited as "particularly worrisome" a lack of data for more than 200 threaded rods that secure the main suspension cable at its eastern anchorage.
Threads on those rods were "cold rolled" _ mechanically carved at room temperature _ increasing surface hardness of the steel at the threaded ends, the oversight committee, Chung and Thomas agree. The harder the steel, the more vulnerable to becoming brittle from hydrogen contamination.
The use of such large rods is unprecedented, Chung and Thomas wrote, so academic literature offers no way to assess their vulnerability to cracking. The rods "might be more susceptible to (hydrogen-embrittlement) cracking than any other anchor rods on the new Bay Bridge," Chung said, including some of those being replaced. Yet no hardness tests have been completed for the threaded portions of those rods.
Caltrans is conducting tests to simulate the long-term durability of some rods, including two cold-rolled samples. One involves soaking them in a salt solution and measuring their ability to withstand gradually increasing stress. Preliminary results look encouraging, but the tests will not be completed until the middle of next year, said bridge spokesman Andrew Gordon.
The tests should provide useful data to help show the load an anchor rod can sustain before it fails because of stress corrosion cracking, Chung said. But they might lend a false sense of security, because "there are no accelerated corrosion tests that can predict (the) long-term corrosion performance of a material."
The stakes for making such predictions are high. "If the rods go," Chung said in an interview, "the whole bridge would come down."
(c)2013 The Sacramento Bee
Join the Discussion
After you comment, click Post. You can enter an anonymous Display Name or connect to a social profile.