Expert: Over 600 Bay Bridge rods too hard
Jaxon Van Derbeken | San Francisco Chronicle
Updated 10:52 pm, Friday, May 31, 2013
More than 600 high-strength rods and bolts used to secure seismic equipment on the new eastern span of the Bay Bridge are harder than the level at which a Caltrans expert says they are vulnerable to cracking, newly released test results show.The results are a key factor in Caltrans' upcoming decision about what to do with more than 2,000 high-strength, galvanized steel rods and bolts on the bridge. The tests were ordered after 32 rods cracked when workers tightened them on the span in March.
The scheduled Sept. 3 opening for the $6.4 billion bridge hinges on Caltrans' verdict. If the span can't be finished by then, transportation officials say, it could be several additional months before conditions are right for a new opening date.
The problem with hard steel that has been galvanized - dipped in molten zinc, an antirust measure - is that it is susceptible to being invaded by hydrogen. That can lead to cracking.
Hundreds of hard rods
The hardness question arose after the 32 rods on seismic stability structures failed. Caltrans said it wasn't sure how hard its other steel fasteners were, and ordered an audit of records and field testing of hundreds of rods.
The data that the agency released this week show that 544 rods anchoring other seismic-stability structures and load-distributing bearings average 35 on a hardness scale developed by the American Society for Testing and Materials.
Another 96 rods used inside the seismic bearings average 36, based on preinstallation quality-control tests, Caltrans said. The rods can't be field checked because they are not accessible on the new bridge.
Above safety level
Those levels are above the at-risk hardness threshold of 34 set by John Fisher, a renowned civil engineer and bridge specialist and one of three members of Caltrans' panel of independent bridge experts. Rods that hard can be invaded by hydrogen if they are placed under high stress, Fisher told The Chronicle.
Caltrans ordinarily would not have used such hard rods, but made an exception to its own rules for the eastern span. Officials have never thoroughly explained the reason.
Fisher, who said Caltrans' call to use the galvanized rods was "not well-thought through," said Thursday that he would await the results of corrosion-simulation tests on the rods before deciding whether to urge the agency to replace those with a hardness level of 34 or greater.
"I think we ought to wait and see what the results of the tests are," Fisher said. "I don't see a great risk in doing that."
The tests, he said, will "give you an idea as to whether they are susceptible to the environment."
No more cracks
Fisher also noted that no additional cracked bolts have been discovered since the 32 failed in March.
The corrosion-simulation tests involve dunking the rods in tanks filled with salt water and progressively raising the tension on them over 25 days. The idea is to simulate 10 years' worth of exposure to a marine environment rich in hydrogen.
Caltrans expects to have the results by late July.
Brian Maroney, the chief engineer on the bridge project, has said replacing hundreds of bolts would be "one alternative" if Caltrans concludes they are excessively vulnerable to corrosion. "We might do that," he said in an interview last month.
If Caltrans has to replace hundreds of bolts, it could add months to what has already been a decadelong construction project.
Bridge options
Steve Heminger, executive director of the Metropolitan Transportation Commission and a member of a bridge oversight panel, said that, depending on corrosion-test findings, many of the rods may ultimately be deemed "acceptable" as is. Others could be replaced after the bridge is open.
Caltrans spokesman Andrew Gordon said Fisher has told Caltrans that any rod with a hardness above 34 is suspect and therefore, "You need to dig deeper and investigate more and consider tension levels and other testing data.
"We are following that advice," Gordon said. "We haven't made any decisions. There is ongoing testing and investigation into these additional bolts. Once we have the results of that, we will seek the counsel of the seismic peer review panel, as we have throughout this process."
Source: http://www.sfgate.com/bayarea/article/Expert-Over-600-Bay-Bridge-rods-too-hard-4567801.phpCheck out http://groups.yahoo.com/group/californiadisasters/
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