New bridge bearings could withstand 8.2 quake


The earthquake simulator was shaking the equivalent of an 8.2 quake and the bridge is not only still standing, it is completely undamaged.

"What we're demonstrating today is a new performance objective. We wish to have structures, rail lines, and highway systems that are fully functioning after the biggest earthquake that could happen," says Victor Zayas, Ph.D., from Earthquake Protection Systems.

U.C. Berkeley researchers say for the last 30 years, engineers have been designing structures that won't collapse, but might be badly damaged. Now they say technology is available so that a bridge will not only stay up, it will stay open.

Berkeley engineers put a 30-foot scale model bridge with rails and a scale train on a shake table, and subjected it to the ground motion and magnitude of some of the worst quakes in modern history -- including 1985 in Chile, 1995 in Kobe, Japan, and 1994 in Northridge.

A new kind of bearing -- a three-pendulum seismic isolation bearing -- successfully absorbs the shock and saves the bridge.

"The advantage of this is it's very simple mechanically. It's very dependable, because it's simple and it can be easily manufactured," says Stephen Mahin, Ph.D., from U.C. Berkeley.

When the new eastern span of the Bay Bridge opens in 2013, it will not have this technology, but a Caltrans animation shows how it's expected to perform in the most severe possible quake.

Lead researcher Stephen Mahin says it could be some time before the new bearing is used here.

"I think we have to see whether people use this. One of the aspects is engineers are very conservative and slow to adopt new technology," says Mahin.

The bridge design demonstrated on Wednesday has not yet been built anywhere in the world.

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