Construction blunder looked at in bridge tower's rod problem
By Jaxon Van Derbeken - San Francisco Chronicle
Updated 8:57 pm, Wednesday, October 1, 2014
Caltrans officials are investigating whether about 400 high-strength rods holding down the tower on the new Bay Bridge's eastern span were exposed to water because workers adjusting them in 2011 broke their watertight seals to surrounding grout.Engineers with the state agency say they found standing water in 95 percent of the sleeves holding the tower's 423 anchor rods. They suspect the water got in when the base was flooded during storms.
Caltrans officials say workers with the bridge's main contractor, the joint venture American Bridge/Fluor, tensioned the 25-foot-long rods after the fasteners had already been sealed with watertight grout and caulked.
That can break the seal with the grout, creating a tiny gap between it and the rods, experts said Wednesday.
"It ruins the seal," said Lisa Fulton, an engineer and corrosion expert in Berkeley. "They can't disturb the grout — the grout has to be poured after the rods are tensioned."
She said water could easily travel down the gap and settle at the base of the rods, where they are secured by nuts under steel plates. That base cannot be reached without removing the grout, which fills most of the 15-foot sleeves that hold the rods.
Experts point to Caltrans' admission this week that water was found at the base of one of the rods when it was removed for testing last year.
"When you are tensioning, you put the caulk and the grout under pretty high stresses and they just can't handle it. Then you get a little rain or moisture, and you are off to the races," said Russ Kane, a corrosion expert in Houston. "It's not rocket science; it's the basics. Nobody is thinking about the basics."
Randy Rentschler, spokesman for the Metropolitan Transportation Commission, said the agency has asked Caltrans to check the theory.
"We want to know whether there is a correlation with water being found in rods that were tensioned twice," he said. "The first thing we need to do is be methodical in determining the most likely cause of why the water is there, to see if the theory is correct."
Caltrans is conducting tests to see whether any of the rods has become corroded from sitting in the water. It's unclear how the agency would respond if evidence of corrosion is found, because there is no room in the tower chamber to maneuver a replacement rod into place.
Caltrans has downplayed the risk of corrosion on the rods, saying they are not tensioned high enough to snap, the way 32 rods did last year on the new bridge's seismic stabilizer structures.
However, Yun Chung, a retired Bechtel engineer and expert on steel fasteners, said the stress on the tower rods is typically concentrated at the bottom, where water could now be lurking. That was the case with the rods that failed last year, he said.
Chung said his fear is that "it's the same thing happening all over again."
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