Bay Bridge's new defect poses risk in earthquake
By Jaxon Van Derbeken
Steel rods that anchor the Bay Bridge eastern span's massive main cable have shifted since they were installed and are now perilously close to sharp-edged plates inside the belly of the new bridge, a problem Caltrans acknowledges could take months and millions of dollars to fix.
Caltrans engineers say more than 200 high-strength rods could be jerked in a major earthquake into those sharp edges, risking damage to the main cable and possibly threatening the bridge's stability.
"We need to do whatever we need to do so this does not happen," Brian Maroney, Caltrans' chief engineer on the bridge, said Thursday.
Caltrans has known about the problem for several months, but Bay Area transportation officials who will soon be responsible for maintaining the bridge say they learned of it only recently. They want it dealt with before the state officially turns over the bridge to local authorities, which is supposed to happen in August.
It's the latest in a string of embarrassing revelations about the $6.4 billion bridge, beginning with the failure of 32 high-strength, galvanized rods on a seismic-stability structure in March 2013. Since then, questions have been raised about the reliability of hundreds of other rods and bolts, a state investigator reported that bridge builders accepted Chinese-made deck sections that didn't fit right, and Caltrans discovered that huge, hollow steel structures that support the road decks leak when it rains.
The latest problem came to light when Caltrans inspected the rods that hold both ends of the bridge's nearly mile-long cable at the eastern end of the suspension portion of the bridge to see if they were at risk of cracking.
The cable is draped over the bridge's tower and is anchored into two 150-foot-long steel chambers under the road deck. At the anchorage, the cable fans into 137 strands on both the northern and southern sides of the bridge. Each strand connects to a steel rod, 28 to 32 feet long.
The rods, in turn, run through holes to the steel chambers. The bridge's builder, a joint venture called American Bridge/Fluor, got Caltrans' permission to make the last hole larger than the others to make anchoring the cable strands easier, something that inadvertently gave the rods extra room to move around.
The rods did move and, in too many cases, now there's no longer room to spare between them and the smaller holes in the steel reinforcement plates.
Caltrans engineers don't know for certain why the rods slipped out of position. One theory is that they were originally centered properly, but shifted when a temporary steel underpinning was removed in November 2012.
No one checked the cable anchor rods at the time. Caltrans does not believe the rods shifted over time because they were pulled too tightly to allow for movement.
Crews didn't discover the problem until after the rods on the seismic-stability structure snapped last year, prompting Caltrans to open its investigation of the rods and bolts elsewhere on the bridge.
A recent survey found that 205 out of the 274 cable rods are so far off center that either they have to be readjusted or some of the steel on the plates must be cut away, to avoid the pinch point with the rods. Two of the rods are already touching the surrounding steel.
A pinch point can amplify stress, said bridge engineer Maroney.
"I don't want a sharp corner of the (steel) stiffener coming into contact with the rod," Maroney said. "The rod will move, then bend. The sharp edge on the bent steel creates a kink, a change in the angle that causes high stress. You don't want to do that.
"It does need to be resolved," he said. "If you have an earthquake, these things start to vibrate. You don't want kinking at a sharp point on the edge of stiffener."
Maroney added, "This is sacred ground. The cable and the tower are the backbone and the spine, critical elements to this bridge. I don't want to be worrying about the cable system."
He said the crews will first try to loosen the nuts on the rods and re-center the huge fasteners. If that isn't possible, workers will have to somehow widen the openings in 2-inch-thick steel plates to create more room for the rods to vibrate in a quake.
Andrew Fremier, deputy director of the local agency overseeing the bridge project, the Metropolitan Transportation Commission, said he learned about the problem just this month. He said his agency wants to know why Caltrans did not include the off-center rods on a list of pending maintenance issues with the new bridge that the state turned over to the oversight board May 6.
"This is not in the list," Fremier said. "We feel it should be."
He said the cost is expected to be at least $2 million, a figure Maroney did not dispute.
Fremier said the repairs could take until the end of the year if Caltrans puts the job out to bid instead of giving it to American Bridge/Fluor. He said the cost will probably be paid for out of the bridge's contingency fund, which has a balance of $85 million in toll-payers' money.
Maroney said the problem will be dealt with by the time the span is turned over to the commission, which he said could happen by October.
Bob Bea, an emeritus professor of civil engineering at UC Berkeley and risk analysis expert, said the latest snafu was a "predictable surprise" because of the builder's decision to make one hole bigger than the others.
"It's something that you could have predicted if you thought more about it, but you didn't think deeply about it," he said. "It's easy for these damn details to sneak through the design process - that's what seems to be going on here. I wonder what other things are lurking in the darkness."
Caltrans engineers say more than 200 high-strength rods could be jerked in a major earthquake into those sharp edges, risking damage to the main cable and possibly threatening the bridge's stability.
"We need to do whatever we need to do so this does not happen," Brian Maroney, Caltrans' chief engineer on the bridge, said Thursday.
Caltrans has known about the problem for several months, but Bay Area transportation officials who will soon be responsible for maintaining the bridge say they learned of it only recently. They want it dealt with before the state officially turns over the bridge to local authorities, which is supposed to happen in August.
It's the latest in a string of embarrassing revelations about the $6.4 billion bridge, beginning with the failure of 32 high-strength, galvanized rods on a seismic-stability structure in March 2013. Since then, questions have been raised about the reliability of hundreds of other rods and bolts, a state investigator reported that bridge builders accepted Chinese-made deck sections that didn't fit right, and Caltrans discovered that huge, hollow steel structures that support the road decks leak when it rains.
The latest problem came to light when Caltrans inspected the rods that hold both ends of the bridge's nearly mile-long cable at the eastern end of the suspension portion of the bridge to see if they were at risk of cracking.
The cable is draped over the bridge's tower and is anchored into two 150-foot-long steel chambers under the road deck. At the anchorage, the cable fans into 137 strands on both the northern and southern sides of the bridge. Each strand connects to a steel rod, 28 to 32 feet long.
The rods, in turn, run through holes to the steel chambers. The bridge's builder, a joint venture called American Bridge/Fluor, got Caltrans' permission to make the last hole larger than the others to make anchoring the cable strands easier, something that inadvertently gave the rods extra room to move around.
The rods did move and, in too many cases, now there's no longer room to spare between them and the smaller holes in the steel reinforcement plates.
Caltrans engineers don't know for certain why the rods slipped out of position. One theory is that they were originally centered properly, but shifted when a temporary steel underpinning was removed in November 2012.
No one checked the cable anchor rods at the time. Caltrans does not believe the rods shifted over time because they were pulled too tightly to allow for movement.
Crews didn't discover the problem until after the rods on the seismic-stability structure snapped last year, prompting Caltrans to open its investigation of the rods and bolts elsewhere on the bridge.
A recent survey found that 205 out of the 274 cable rods are so far off center that either they have to be readjusted or some of the steel on the plates must be cut away, to avoid the pinch point with the rods. Two of the rods are already touching the surrounding steel.
A pinch point can amplify stress, said bridge engineer Maroney.
"I don't want a sharp corner of the (steel) stiffener coming into contact with the rod," Maroney said. "The rod will move, then bend. The sharp edge on the bent steel creates a kink, a change in the angle that causes high stress. You don't want to do that.
"It does need to be resolved," he said. "If you have an earthquake, these things start to vibrate. You don't want kinking at a sharp point on the edge of stiffener."
Maroney added, "This is sacred ground. The cable and the tower are the backbone and the spine, critical elements to this bridge. I don't want to be worrying about the cable system."
He said the crews will first try to loosen the nuts on the rods and re-center the huge fasteners. If that isn't possible, workers will have to somehow widen the openings in 2-inch-thick steel plates to create more room for the rods to vibrate in a quake.
Andrew Fremier, deputy director of the local agency overseeing the bridge project, the Metropolitan Transportation Commission, said he learned about the problem just this month. He said his agency wants to know why Caltrans did not include the off-center rods on a list of pending maintenance issues with the new bridge that the state turned over to the oversight board May 6.
"This is not in the list," Fremier said. "We feel it should be."
He said the cost is expected to be at least $2 million, a figure Maroney did not dispute.
Fremier said the repairs could take until the end of the year if Caltrans puts the job out to bid instead of giving it to American Bridge/Fluor. He said the cost will probably be paid for out of the bridge's contingency fund, which has a balance of $85 million in toll-payers' money.
Maroney said the problem will be dealt with by the time the span is turned over to the commission, which he said could happen by October.
Bob Bea, an emeritus professor of civil engineering at UC Berkeley and risk analysis expert, said the latest snafu was a "predictable surprise" because of the builder's decision to make one hole bigger than the others.
"It's something that you could have predicted if you thought more about it, but you didn't think deeply about it," he said. "It's easy for these damn details to sneak through the design process - that's what seems to be going on here. I wonder what other things are lurking in the darkness."
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