As the toll of earthquake damage to steel-frame buildings mounts, the state has issued an unprecedented advisory urging owners of buildings that suffered cosmetic damage to conduct thorough inspections to check for cracks in supporting columns.
Steel-frame office buildings have long been considered invulnerable to collapse, but the California Seismic Safety Commission issued its advisory this week because engineers have uncovered widespread evidence that steel beams and welds cracked in the Jan. 17 Northridge quake.
Los Angeles city officials said that cracking has been found in the steel frames of at least 50 buildings, constituting at least 10% of the low- to mid-rise structures built in the area since 1970.
Most of the failures occurred in mid-rise buildings of less than 10 stories, but an 18-story twin tower in Warner Center and an unidentified 23-story high-rise elsewhere in the San Fernando Valley also had structural problems.
The failures already have prompted city officials to require more rigorous welding procedures in new steel-frame buildings.
On Thursday, city officials said they plan to announce within two weeks that owners of all steel-frame buildings near the quake's epicenter will be required to conduct inspections for hidden structural damage.
Richard Holguin, assistant chief of the building bureau of the city's building and safety department, said officials are also considering whether to require citywide inspections of such buildings, which made up half of all buildings constructed last year in Los Angeles.
Meanwhile, the mounting damage tally has sparked concerns about the safety of the cloud-piercing towers in Downtown, Century City and elsewhere, even though engineers emphasize that no steel-frame buildings came close to collapsing during the temblor.
"The world is watching," said L. Tom Tobin, executive director of the California Seismic Commission. "There is no question that this has been a wake-up call for the engineering and construction community world wide."
Steel-frame buildings, designed to bend with the enormous forces of an earthquake without breaking, have been considered among the safest to ride out an earthquake. But the commission noted: "Damage was reported to a significant number of steel structures shaken by the Northridge earthquake, raising concerns about the extent and implications of this damage."
