Courtesy of the California Seismic Safety CommissionThe new Olive View Medical Center in Sylmar was severely damaged in the 1971 San Fernando earthquake.
As many as 17,000 older concrete buildings in California could be vulnerable during a major earthquake, according to a new inventory by a coalition of volunteer structural engineers, universities and government agencies.
A number of schools, state and local government buildings, and other vital infrastructure – such as police stations and hospitals – made the list.
During the San Fernando, Loma Prieta and Northridge earthquakes, several concrete buildings constructed before the implementation of modern codes collapsed or were catastrophically damaged.
“One of the problems with the concrete buildings is that they tend to be large," said Craig Comartin, director of the Concrete Coalition project, a group of volunteer structural engineers that wrote the report [PDF]. "When you have a major apartment building, there could be hundreds of people in the building. When one does come down, the potential for deaths or injuries is high.”
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The coalition looked at 23 counties with the highest earthquake risk and population, as well as two cities – Fresno and Bakersfield. The group estimates there are between 16,000 and 17,000 potentially vulnerable concrete buildings in the state. More detailed information for each county surveyed is available at the coalition’s website.
Not all of the concrete buildings identified are collapse hazards or prone to severe earthquake damage, the report notes. The next stage of the project will be a more careful study of specific buildings in order to better understand which are the riskiest structures.
Unlike unreinforced masonry buildings, which structural engineers say uniformly do not perform well in earthquakes, there’s tremendous variability in older concrete buildings.
Understanding what makes a concrete building vulnerable is one of the goals of a National Science Foundation-funded research project at the Pacific Earthquake Engineering Research Center. Under the leadership of Jack Moehle, a civil engineering professor at UC Berkeley, researchers are working on ways to quickly weed out which buildings may need more detailed evaluation and possibly a retrofit.
“If we can provide the tools that would help identify which are the highest risk, then you can develop programs that target those higher-risk buildings,” Moehle said.
Some members of the business community have said they're interested in helping mitigate the risk, but expressed concerns about the cost.
“We as an industry group would be happy to get information out,” said Martha Cox-Nitikman, senior director for public policy and education for the Building Owners and Managers Association of Greater Los Angeles. But some owners have told her that if required to retrofit the building, they might just tear it down.
It’s unclear what the next steps might be to address the older concrete buildings. The state Seismic Safety Commission’s most recent attempt to address concrete structures statewide was more than two decades ago, through a bill by the late Sen. Al Alquist.
“We’ll have more tools to make better decisions, but at this point, we don’t have enough tools in place for me to even surmise,” said Fred Turner, the top structural engineer with the Seismic Safety Commission. “We feel a lot more confident to help make informed decisions now than we did back in the mid-'80s in that we have a lot of publications that talk about the financial and social implications of retrofit programs, whether they be voluntary or mandatory.”