Tens of thousands of older concrete buildings across California represent the state's largest remaining risk of serious damage in a major earthquake, seismic safety officials say.
Constructed as department stores, schools, parking structures and office buildings from the 1930s through the early 1970s, these buildings typically consist of large, open lower stories held up by unreinforced or poorly reinforced concrete pillars.
After several collapsed in the 1971 San Fernando earthquake, seismic safety codes were upgraded to require that any new concrete buildings be better constructed. Many seismic experts say preexisting structures -- known as non-ductile concrete buildings -- need to be retrofitted to bring them up to current standards.
"It's well recognized within the earthquake professional community that many California non-ductile concrete buildings are at unacceptable risk of collapse in moderately strong shaking," said Thomas Heaton, professor of engineering seismology at Caltech.
Because many of the older concrete buildings tend to be filled during the day with office workers, schoolchildren or people parking their cars, the death and injury toll from an earthquake that caused several of the structures to collapse could be staggering, said Heaton.
But building owners and business organizations have long fought efforts to require retrofits, arguing that the risk is overstated. And they say that in some cases, the cost of retrofits comes close to that of razing a building and starting over. Neither the state nor local governments have required that the structures be reinforced.
"If you're going to use a 'sky is falling' scenario, then maybe you can justify" a retrofit requirement, said Carol Schatz, president of the Central City Assn. "But if you're going to put a bunch of commercial property owners out of business in the process, what have you accomplished?"
Property owners and business associations opposed a proposal last year by City Councilmen Greig Smith and Alex Padilla to count the number of unreinforced concrete buildings in Los Angeles. The measure didn't make it out of a council committee.
"We met with a lot of opposition," said Smith, who saw that and a compasion proposal as first steps toward developing a program to retrofit the city's non-ductile concrete buildings and unreinforced parking structures. Smith said he hoped to work with business groups to draft a proposal acceptable to the council.
Older concrete buildings are receiving more focus in part because the state has made headway retrofitting unreinforced masonry buildings and concrete freeway bridges.
While concrete buildings largely withstood the 1994 Northridge quake, the temblor did cause major damage to the Kaiser Permanente Hospital in Panorama City and an office building in West Los Angeles. Local officials were more alarmed a year later by the failure of numerous concrete buildings in a massive earthquake in Kobe, Japan.
State officials have never formally counted the number of non-ductile concrete buildings in California, though the seismic safety commission estimates there are about 40,000 of them. About 8,000 are school buildings, including 239 schools owned by the Los Angeles Unified School District.
Schatz estimates that downtown Los Angeles has 500 of the buildings.
"The non-ductile frame buildings are probably the most dangerous buildings we have," said John "Trailer" Martin, president of the Los Angeles structural engineering firm John A. Martin & Associates.
The buildings can fall, Martin said, because the concrete pillars that hold up the floors are too rigid to withstand heavy shaking. To prevent collapse, engineers design buildings with strong walls -- known as shear walls -- connected to the pillars to provide a stronger framework to hold the heavy floors above. They also put heavy steel inside any concrete posts. To retrofit an old building, shear walls can be added, and columns can be wrapped in stronger, more resilient material than the old concrete.
Earthquakes such as the one this weekend in Pakistan heighten the sense of urgency for retrofits, some experts said.
But Schatz, skeptical that the buildings pose a real risk of collapse, said that requiring owners to pay for retrofits would be tantamount to asking them to tear down their property altogether. As of about a year ago, the cost of retrofitting one building could be as high as $14.4 million -- almost as much as starting over. And construction costs -- particularly for the steel that is necessary to reinforce the concrete pillars -- have increased significantly since then.
Worldwide, non-ductile concrete buildings are believed to be the fastest-growing cause of death from earthquakes, said Fred Turner, the top structural engineer for the California Seismic Safety Commission.
Such construction is popular in Asia and the Middle East, he and others said, because it's relatively cheap and allows a building's bottom floor to be open, like a traditional marketplace or plaza.