Earthquakes in Japan and New Zealand have focused attention on quake safety and the vulnerability of brittle concrete buildings. But efforts to identify and retrofit them have stalled because of the high cost.
California has failed to identify and retrofit thousands of brittle concrete buildings despite years of warnings from scientists that the structures are highly vulnerable to collapse during a major earthquake.Officials have known as far back as the 1971 Sylmar quake that such buildings can collapse, but efforts to address those weaknesses have stalled because of the high cost of retrofitting the buildings.
Experts estimate that between 25,000 to 30,000 concrete buildings were erected before building codes were strengthened in the mid-1970s, including some heavy clusters in downtown Los Angeles and along Wilshire and Hollywood boulevards.
The devastating earthquakes in Japan and New Zealand have focused more attention on the vulnerability of such buildings.
For California, the quake in Christchurch was particularly relevant because it served as a fresh reminder of the major weaknesses in so-called non-ductile concrete buildings. Numerous concrete structures failed in New Zealand during the Feb. 22, magnitude-6.3 earthquake, including the six-story Canterbury Television building, where 100 people were believed to have been buried, including many TV station employees and 60 students.
The collapse of the CTV building, which housed a local TV station, clinic and English-language school, was particularly shocking. It was built in 1986, 15 years after the Sylmar earthquake, and after codes had been changed in New Zealand and California to improve buildings' ability to withstand shaking. Yet the CTV building collapsed in a manner consistent with a concrete building, said Thomas Heaton, professor of engineering seismology at Caltech.
Experts both in Christchurch and Los Angeles said such buildings are worrisome because it's so difficult for people inside to survive if large slabs of concrete fall on top of them.
"They're killers. In my opinion, they could take many thousands of lives in a Southern California earthquake, especially one inside the Los Angeles Basin," Heaton said. "When they fail, the failures are just unsurvivable. You just end up with a pile of floor slabs, one on top of another."
Identifying potentially unsafe buildings is crucial, Heaton said, because being in a building designed to withstand major shaking is a "big part of your survivability in an earthquake," Heaton said. "If you choose poorly, you're definitely in harm's way."
In the last decade, the Los Angeles City Council has considered a plan to identify brittle concrete buildings. But the plan's author, Councilman Greig Smith, was forced to shelve the plan as support evaporated and the recession left little money to address the risk.
The California Seismic Safety Commission has also recommended that the state identify brittle buildings, both public and private, and figure out a way to reduce the risk. But lawmakers have taken little action.
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View entire article here: http://www.latimes.com/news/local/la-me-quake-buildings-20110317,0,5272824.story
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