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New Bay Bridge Defect Spurs Concern

Wednesday, May 21, 2014

More items for Program/Project Management

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Steel rods that anchor the massive suspension cable on the new San Francisco-Oakland Bay Bridge have shifted since installation and are now too close to sharp plates inside the bridge, state engineers report.

A strong earthquake—like the one, for example, that necessitated building of the new span in the first place—could cause the rods to vibrate into the sharp steel edges, risking damage to the main cable of the $6.4 billion bridge, California Department of Transportation engineers told SFGate.com Thursday (May 15).

Caltrans has known about the problem for months but did not include it on a list of maintenance issues presented May 6 to the Toll Bridge Program Oversight Committee at its first public meeting, the newspaper said.

Wikimedia Commons / Caltrans

Steel rods that anchor the bridge's suspension cable have shifted, putting them too close to sharp steel plates. Engineers worry that a major earthquake could vibrate the rods into the plates, causing damage to a key seismic stability component.

The Oversight Committee is comprised of representatives from Caltrans, the California Transportation Committee, and the Bay Area Toll Authority.

Out of Place

The single-tower, self-anchored suspension bridge features a unique design in which the 137-strand main cable loops over the tower and under the bridge. There, the strands are inserted into sockets that are attached to thread rods; the rods pass through the walls of two chambers on the bridge's east end, where they are locked in place.

Caltrans discovered the issue while inspecting the rods for risk for cracking.

Of the 274 rods, 205 are less than the required 10 millimeters from the inner surface of the holes they pass through. Two rods are already touching the steel, SFGate.com reported.

Andrew Fremier, deputy executive director of the Bay Area Toll Authority and deputy executive director of operations for the Metropolitan Transportation Commission, said he learned about the problem this month. Fremier said his agency wanted to know why Caltrans had not included the problem in the list of pending maintenance issues.

Screenshot via Fluor

The self-anchored suspension bridge features a unique design in which the cable strands are looped over and under the bridge, as demonstrated in this video from Fluor.

The Bay Area Toll Authority will be responsible for the bridge's maintenance once construction is officially complete sometime later this year. The bridge opened to traffic in September 2013.

Avoiding Kinks

According to SFGate.com, American Bridge/Fluor, the joint venture contracted to build the bridge, made one of the holes larger than the others to make it easier to anchor the cable strands. The change was done with Caltrans' permission, but now it is giving the rods extra room to move.

"I don't want a sharp corner of the (steel) stiffener coming into contact with the rod," Brian Maroney, Caltrans' chief engineer on the bridge, told SFGate.com.

"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," Maroney explained.

"It does need to be resolved. If you have an earthquake, these things start to vibrate. You don't want kinking at a sharp point on the edge of stiffener."

 'Not Urgent'

Fremier told SacBee.com that the problem is seen as "important but not urgent."

Crews will first try to loosen the nuts on the rods and recenter the rods. If that isn't possible, they will have to find a way to widen the opening in the steel plates to make more room for the rods to vibrate in an earthquake.

Fremier said repairs could cost at least $2 million and take until the end of the year, according to several media reports.

BayBridgeInfo.org

The new Bay Bridge has faced multiple issues, including broken bolts last spring, a leaking chamber this spring, and recent reports of corrosion on some of the cable strands.

Caltrans started investigating bolts and anchor rods all over the bridge after massive bolts that connect the underwater foundation and concrete pier cap started breaking last year.

The bridge still opened on schedule, but has faced numerous problems since then.

Leaking, Cracking Reported

A rain storm in February revealed hundreds of leaks in a chamber that was supposed to be watertight.

In April, The Sacramento Bee reported that several of the rods' threads had patches of white and red-brown rust and some of the strands showed rust and "crack-like indentations" where they join the sockets.

Andrew Gordon, a spokesman for Caltrans, told The Bee in an email that that the rust was attributable to "metal shavings/particles generated by grinding and other work."

Several reports about the bridge and its oversight have emerged since September, drawing the attention of the state's Senate Transportation and Housing Committee and its chair, Sen. Mark DeSaulnier (D-Concord).

DeSaulnier has led the committee through a series of informational hearings on improving megaprojects, lessons learned from the Bay Bridge project and, most recently, on reforming Caltrans.

   

Tagged categories: Bridges; Department of Transportation (DOT); Design; Project Management

Comment from Tony Rangus, (5/21/2014, 9:28 AM)

For those of you who work for American Bridge & Fluor, has either company come out to publicly respond to the news reports, Caltrans findings or the report published by the two independent metallurgists?


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