Caltrans: New Bay Bridge Will Survive Big One

Tuesday, Oct 13, 2009  |  Updated 11:30 AM PDT
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"The Fix Is In Place"

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Bay Bridge Seismic Safety Features

Twenty years after an earthquake brought down part of the Bay Bridge, transit planners have designed a replacement to withstand shaking.

"The Fix Is In Place"

C.C. Myers President Dan Himick talks to reporters about the overnight work to fix a crack found in the Bay Bridge during the seismic retrofit project.
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 The San Francisco-Oakland Bay Bridge will be one of the safest  places to be during a major earthquake when seismic improvements are  completed in a few years, California Department of Transportation Commission spokesman Bart Ney said today.
     
"I'd want to be on the new bridge in an earthquake when it's done," Ney said while leading reporters on a tour of the 1.2-mile-long skyway  section of the new eastern span of the Bay Bridge, which will be completed next year.

From the new skyway section, Ney pointed at a spot where a 250-ton section of the existing eastern span collapsed during the Loma Prieta  earthquake about 20 years ago, on Oct. 17, 1989.

He said years of seismic innovations and enhancements on the entire 8-mile-long bridge, from San Francisco, are making the bridge much safer than it was before.

Although some people have complained that it has taken too long to upgrade the span, Ney said one benefit of the lengthy process is that Caltrans has been able to take advantage of recent advances in technology  that will make the bridge safer.

He said, "When the bridge is complete, it's going to be one of the most seismically advanced structures in the world."

An example is 60-foot-long hinge pipe beams, which Ney said are designed to absorb the energy of an earthquake by deforming in the their middle, thus minimizing the damage to the bridge's main structure.

Hinge pipe beams that are damaged can then be quickly removed and replaced after an earthquake, he said.

Ney said the new eastern span of the Bay Bridge is still scheduled to open in 2013.

In addition to the skyway section, work has been completed on the western approach to the bridge and the western span.

Yet to be completed are the transition section at Yerba Buena Island, the self-anchored suspension span and the touchdown on the Oakland  side of the bridge.

Ney said the suspension span's single, 525-foot tall tower will be made up of four separate steel legs connected by shear link beams which allow the legs to move independently.

The beams are designed to absorb most of the seismic energy during a quake and protect the tower from catastrophic damage, he said. The damaged beams can later be removed and replaced.

Ney said the new bridge is designed as "a lifeline structure," meaning that it's supposed to be immediately available for emergency services after an earthquake.

He said the new span might be closed to regular traffic for a short time after a major quake because it could be out of alignment, but Caltrans officials hope to place steel plates on the span so emergency  vehicles can cross the bridge.

Ney said the new bridge isn't designed to withstand a specific level of earthquake as measured by the Richter scale. Instead, Caltrans designed the bridge to withstand the largest conceivable earthquake that  could occur in a 1,500-year period, he said.

"We designed it to withstand ground motions from epicenters from several earthquakes," Ney said.

Anthony Shakal of the California Department of Conservation said monitoring equipment that will be embedded throughout the bridge will provide  data that will help better understand earthquakes by measuring how the bridge responds to ground motion in a quake.

Shakal said that after a temblor, the sensors will transmit the data to create a digital map showing the location and intensity of seismic activity and ground motion.

Crews can use the maps to determine potential damage to infrastructure, including roads and water lines, he said.

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