Bay Bridge tower welds flawed, need repairs
05/01/2013 2:44 PM
10/08/2014 10:42 AM
Welds on the iconic tower of the new San Francisco-Oakland Bay Bridge are flawed and must be repaired, compounding other problems that have beset the project and could delay its planned September opening.
Sources confirmed that the California Department of Transportation is working with contractors to fix defects on portions of 20 welds, each nearly 33 feet long and up to 4 inches thick – a protracted process that has been under way for months. The welds are necessary for the tower to withstand a major earthquake.
The September opening for the $6.4 billion structure is already at risk because of numerous broken and suspect bolts, and an ongoing examination of the tower's foundation.
Yoni Adonyi, chairman of Welding and Materials Joining Engineering at LeTourneau University in Longview, Texas, said industry experts have known about the defective Bay Bridge welds for months and have discussed Caltrans' work to repair them.
Bridge spokesman Andrew Gordon did not provide answers to detailed questions about the state of the defects or whether repairs would be completed before the scheduled bridge opening date.
"There are millions of welds on the bridge, and this issue involved about 20 of them," he said in a written statement. "This is not a safety problem, and these welds do not affect structural stability. We have consulted with top industry experts, and we are on top of the problem. This is not an unusual issue, and this will not affect the schedule for opening the bridge."
Case Western Reserve University professor Arthur Hucklebridge, an expert on seismic issues in bridge construction, said the welds are clearly important for structural safety in a major quake.
"These welds would not impact the load capacity – the weight of the traffic and the tower. But for the tower base to behave as designed during an earthquake, they are necessary," he said. "That's why (Caltrans is) going to the trouble to fix them."
The builder, a joint venture of American Bridge Co. and Fluor Corp., created the welds with the "electroslag" method – a relatively inexpensive process that can produce long, thick welds in a fraction of the time required by some other welding methods.
Karl Frank, chief engineer of Hirschfeld Industries, an Austin, Texas-based steel fabricator, said in an interview that he had discussed the Bay Bridge welds with people involved in their production, in part to compare his own company's more favorable electroslag experience.
Frank said his contacts described Bay Bridge defects as cracks, but he did not know how many were affected or how long repairing them might take.
The welds connect massive steel plates between the four legs of the 525-foot tower at its base just above the water line – creating a monolithic structure required for seismic stability.
When welds cool from a liquid to a solid state, they tend to shrink, sometimes causing cracking. Frank said that because the Bay Bridge welds support a rigid box structure, "you are getting much more restraint that can lead to cracking – no matter what (welding) process you use."
But Frank, a professor emeritus at the University of Texas and a recipient of a Lifetime Achievement Award from the American Institute of Steel Construction, said that "most of us would have shied away from that job" due to a lack of experience with its unusual scale and environment.
"I'm not sure exactly why – or if anybody knows why – the problems occurred," Frank said, particularly because the team of engineers involved was experienced and mockup tests went smoothly.
Engineers involved with the project wrote last year in a trade publication that the welds are the longest of their kind ever created, and that their production was nearly problem-free.
In 1977, the Federal Highway Administration declared a moratorium on electroslag welding on bridge projects that used federal funds because the technology sometimes created defective or fracture-prone welds. An innovation that allowed less welding material to be used and improved reliability – "narrow gap electroslag welding" – created tougher welds suitable for bridges, according to William J. Wright, a welding expert and professor at Virginia Technical University.
The moratorium was lifted by federal authorities in 2000 for some bridge applications.
Frank called electroslag welding "a very good method."
"We're using it everyday" in a computer-controlled, automated process, albeit with different materials than used for the Bay Bridge job, he said. "It's a very reliable procedure (that allows) a great increase in productivity."
But industry skepticism about the method remains common.
"If this (narrow-gap) improvement were so significant, then everyone would have been using it everywhere. That didn't happen," said Adonyi, a recent recipient of a national research award from the American Association of State Highway and Transportation Officials.
Part of the reason was psychological, he said.
"With any technology, once it gets a bad name, it's very hard to undo that bad name," Andonyi said. He referenced the 1970s-era Ford subcompact that sometimes exploded in collisions. "It's like if you came out with a car called the Pinto, you'd expect it to catch fire," he said. "No one would buy it."
Adonyi said the complexity of narrow gap electroslag equipment also has hampered its adoption.
"It's like a space shuttle launch. Everything has to work perfectly," he said. "You set up the machine, you push the button, and hope for the best."
But Adonyi said that as far as he understood, the Bay Bridge welds – whose production was detailed in industry publications – were correctly crafted and followed careful research and testing.
"I am sure nobody did anything wrong," he said. "With any manufacturing process, sometimes you have problems."
But when flaws occur, it often means that some aspect of the rigorous welding code requirements were not followed faithfully, said Wright, who noted he was not familiar with the details of the Bay Bridge situation. Moisture, perhaps from high humidity in the marine environment of the job site, might have played a role.
"If you get moisture introduced into a crack, you will get hydrogen cracking in any weld," Wright said.
Hydrogen contamination is considered a likely cause for 32 bolts breaking in March on seismic equipment on the eastern pier of the suspension span of the bridge. A remedy for the problem, its costs and whether the bridge opening must be delayed for a workaround have yet to be determined. Transportation officials hope to announce a plan May 8.
With the welds, in general, "even the smallest crack, subjected to fatigue, could propagate and lead to a joint failure," said James A. Swanson, an associate professor and Civil Engineering Program director at the University of Cincinnati.
Weld cracks can be repaired, no matter how large, experts said, by excavating the defects – melting the metal and removing it – then refilling the gaps with fresh welds. The electroslag method, which completed each of the welds at the rapid clip of about 4.5 hours per weld, cannot be used for such repairs, according to experts.
After the welds were made, ultrasonic testing, which uses sound waves to probe the welds, found that less than 5 percent of the total weld material required repair. Caltrans has not said how much of the welds actually must be repaired, but the earlier estimate apparently proved overly optimistic.
Call The Bee's Charles Piller, (916) 321-1113. Follow him on Twitter @cpiller.
This story was changed May 3 to correct the institutional affiliation of James A. Swanson. He is an associate professor and Civil Engineering Program director at the University of Cincinnati.
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