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Crews work on the Bay Bridge in San Francisco, Wednesday, Oct. 28, 2009. The San Francisco-Oakland Bay Bridge has been closed indefinitely after a rod installed during last month's emergency repairs snapped, causing a traffic nightmare for the 280,000 motorists who cross the landmark span every day.(AP Photo/Marcio Jose Sanchez)

Restoring use of the Bay Bridge depends on crews eliminating the friction that caused parts of a steel brace to fall from a faulty Labor Day repair, Caltrans officials said.

The transportation agency late Wednesday still was not predicting a reopening time and date for the region's busiest bridge, although one repair contractor suggested the repairs might be done as early as midday today.

Caltrans worked under a glaring public spotlight after three heavy pieces of a metal splint — two heavy tie rods and a cross piece — came crashing down on bridge traffic Tuesday night. No one was seriously injured, but the bridge was closed as crews began repairing and modifying the brace.

Caltrans and its lead contractor attributed the failure to wind- and traffic-induced vibration that caused grinding on a 20-foot-long metal tie rod that snapped like a paper clip bent back and forth too many times.

"The vibration leads to the rubbing," Caltrans spokesman Bart Ney said Wednesday in a briefing for reporters. "We are making several enhancements to address that issue."

Ney would not predict when the bridge would reopen. That will happen when Caltrans is satisfied that contractors have modified and repaired the giant brace installed over Labor Day weekend to protect a cracked bridge beam called an eyebar.

The brace acts as a giant splint with long steel rods connected to metal sleeves above and below the cracked beam.

One UC Berkeley engineering professor said Wednesday he believes the braces are an inadequate fix for a 73-year-old bridge.

"It's a Band-Aid fix," professor Abolhassan Astaneh-Asl said. "They rushed this repair over Labor Day, and now they refuse to acknowledge it's an incorrect design."

Caltrans officials defended the brace, and said they are improving it to better in sulate it from vibrations on the heavily used bridge in the middle of a wind-swept bay.

To reduce friction, repair crews Wednesday were reaming out larger holes where the tie rods pass through the brace.

"There will not be metal on metal," Ney said.

Some of the welds in the brace will be redone to better hold the entire unit together, he said.

The winds buffeting the Bay Bridge spiked two hours before the Tuesday failure of the support structure, Caltrans said.

"The early diagnosis is that a fatigue-related crack in a tie rod, exacerbated by yesterday's wind storm," caused the failure, Ney said.

Vibrations from the 260,000 vehicles crossing the bridge per weekday also contributed to the problem, said Ed Puchi, treasurer of MCM Construction of Sacramento, the lead repair contractor.

Puchi said the repairs probably will be complete sometime today.

The Federal Highway Administration sent engineers Wednesday to determine the failure's cause.

Spokeswoman Nancy Singer says her agency relied on state inspection reports and did not itself check the original Labor Day weekend repair.

Caltrans had touted the Labor Day fix as a first-of-its-kind innovation.

"It's a design that hadn't been done before because we haven't seen a crack in an eyebar before," Ney said.

"Wind is something that should have been accounted for (in the design)," Ney said. "The incident is something I can't imagine anyone would feel confident about. We have identified fatigue as a factor and the new design should address that."

C.C. Myers, the company that installed the fix, is not the lead contractor on this job. Ney said the Rancho Cordova contractor was not replaced because its repair failed. MCM Construction was already on site, building a portion of the new east span of the Bay Bridge, when the tie rods broke, he said.