MONDAY, APRIL 22, 2013
Missing paperwork, ignored testing, and hydrogen—all problems flagged years ago—potentially contributed to the newly cracked bolts on California’s Bay Bridge, state transportation officials now say.
Bolts used for seismic stability on the Bay Bridge's eastern span retrofit project recently broke loose just days after being tightened.
Initial testing showed that hydrogen was to blame, but layers of other problems dating back several years point to a series of missteps that could have prevented the problem earlier.
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| Photos: Caltrans |
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Caltrans ordered extra testing on the bolts in 2008, but the contractor disputed whether they had to be done. Now, the bolts are starting to break. |
In early March, workers started tightening nuts on both ends of 96 bolts, also called anchor rods, which were installed for seismic stability.
The massive bolts—ranging from nine to 24 feet long and three inches in diameter—popped loose just days after crews started tightening them, damaging the bolts.
Caltrans engineers ordered tests on the bolts in 2008, but those tests were never done after the contractor disputed whether they were required.
Caltrans recently released hundreds of pages of documents that showed its inspectors found structural integrity issues with some of the bolts years ago.
Twice-Baked Bolts
The Metropolitan Transportation Committee was briefed on the problems April 10, and Tony Anziano, Caltran's toll bridge project manager, told MTC that there was previously a "paperwork" problem.
After the bolts were tempered with 800-degree heat, the contractor reportedly failed to produce documents showing the bolts had been properly heat-treated, so Caltrans ordered that they be baked again, Anziano said, according to the San Francisco Chronicle.
Because they were heated twice, the bolts were much harder than required by industry standards; however, Caltrans believes that extra hardness may have ultimately led them to fail.
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The bolts could have been easily replaced before the bridge deck was placed on top of them. Now, officials are trying to figure out how to repair them. |
Tensile strength tests showed the bolts to have the strength of 170,000 pounds per square inch, which is well beyond the minimum required level of 140,000 pounds.
After being heat-treated, the bolts were galvanized and delivered to the bridge in 2008, when they were installed into holes in the concrete caps. These holes later filled with rainwater.
Caltrans accepted the bolts because the agency believed the hydrogen had been eliminated from the galvanizing process, Anziano said. The agency is unsure when the hydrogen got into the steel bolts, as they sat in place on the bridge for five years before being tightened.
Extra Testing Denied
On Oct. 31, 2008, Caltrans' then-resident engineer directed American Bridge/Fluor, the project's main contractor for the eastern span, to conduct additional magnetic particle testing on the bolts, state documents show.
However, the company's project director, Michael Flowers, replied to Caltrans on Nov. 3, 2008, saying that the agency "does NOT require [emphasis in original]" the bolts to be tested. State documents do not show a reply from Caltrans, and there is no indication that the tests were ever performed.
American Bridge/Fluor has not commented since the documents were released, and the company did not respond Friday (April 19) to a request for comment.
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Originally scheduled for completion Labor Day weekend, the $6.4 billion Bay Bridge might be delayed.   |
Inspectors said that the bolts, made by Ohio-based Dyson Corp., had failed to meet certain testing criteria on three occasions.
These tests, designed to detect cracks in the first set of 96 bolts, would have been performed when the rods were still accessible. Now, access to the bolts is limited because the rods go entirely through the concrete cap in some areas.
"They actually have to be extracted as far as you can pull them out, then you have to cut a piece off, extract a little bit further, cut a piece off," Anziano said. There is only five feet of clearance to work with, and the rods are at least nine feet long.
"Right now, the toll bridge program is conducting a very thorough investigation into what happened and what caused the bolts to break," Caltrans spokesman Andrew Gordon told KGO-TV, the local ABC affiliate.
"We know that there was an excess of hydrogen. We're looking into at what point in fabrication process this became a problem," Gordon said.
The $6.4 billion Bay Bridge project was expected to be completed Labor Day weekend of 2013.. Officials have not stated whether the project will be delayed.
Tagged categories: Bridges; Concrete; Department of Transportation (DOT); Galvanized steel; Performance testing; Quality Control; Retrofits; Steel
