Northridge Anniversary Spurs Calls for Review of Building Safety

The city of Los Angeles is making plans to take inventory of quake-vulnerable buildings

The looming 20th anniversary Friday  of the devastating Northridge earthquake is providing incentive for Los Angeles city leaders to look again at some of the lessons learned that -- for cost or other reasons -- have yet to be applied.

"We looked at all the policy initiatives that have been sitting idle, quite frankly, for many years," said Councilman Mitchell Englander, during a break in Tuesday's council session.

The council voted to seek funding for building officials to take inventory of structures with designs that gave way during the Northridge quake and even previously.

Northridge Earthquake: Remembering the Devastating LA Quake 20 Years Later

Also Tuesday, the council heard from Lucy Jones, U.S. Geological Survey seismologist who, under special arrangements announced by Mayor Eric Garcetti, will serve the next year as a Risk Reduction Advisor to the city of Los Angeles.

Jones urged the council to take specific steps to prepare the city for the inevitable significant quakes to come, including the "big one" on the San Andreas Fault.

She spoke of the importance of protecting not only buildings, but also critical infrastructure, such as water delivery and communication. She noted that the internet and cellular phone networks -- now critical in modern communication -- were barely in their infancy during the Northridge quake, and therefore less of a concern then than now. When the shaking stops, the crisis is just beginning.

"What we should be worried about is having a society that will function afterwards," Jones said.

The shaking of the 6.7-magnitude Northridge quake was felt more strongly in the San Fernando Valley than in the more densely populated Los Angeles basin to the south. Any number of faults in the basin, or a major quake on the San Andreas, could generate shaking in the basin comparable to what the Valley experienced in 1994, experts said.

"We're really not ready for that," said Tom Heaton, a professor and director of the Earthquake Engineering Research Laboratory at the California Institute of Technology in Pasadena.

Information and Resources for Southern California Earthquakes

The single deadliest building failure of the Northridge quake occurred in the Northridge Meadows apartment building, where the first story gave way and was crushed by the weight of the top two stories.

Sixteen persons died. Engineers focused on the building's so-called "soft story" design, with a row of tuck-under garages, where overhead door openings lacked the additional support of walls. Heaton noted the vulnerabilities of soft story and certain concrete buildings without steel frames had been made apparent during the 1971 Sylmar Quake, when the Olive View Medical Center collapsed.

The building code was amended, but lawmakers and city officials stopped short of requiring retrofits to strengthen existing buildings. In fact, it is not known with any certainty how many soft story buildings remain in Los Angeles.

That is the reason for the inventory advocated by Englander and Councilman Tom LaBonge. In San Francisco, a preliminary accounting found some 3,000 soft story buildings, in a city with a population only a fifth that of Los Angeles.

Englander expressed hope the inventory could begin next year. He's also seeking state action to provide tax incentives or some other way to defray the cost of retrofits. Associations representing both landlords and renters have expressed concerns about the cost and disruption of retrofitting.

"You've got to create an incentive for those property owners to get the retrofitting done," Englander said.

It's estimated the cost of retrofitting wood-framed soft story apartment buildings can exceed $100,000. It can be even more expensive to reinforce so-called non-ductile concrete buildings, either by spiral wrapping support columns to hold together the structural concrete, or by adding shear walls, as was done in Caltech's Spalding building.

An inventory of non-ductile concrete buildings has been compiled by an academic group. But it declined to make the study public, citing liability concerns. A freeway overpass in the Newhall Pass collapsed in 1971, and also again in 1994.

By then Caltrans had begun a retrofitting program to strengthen support columns, but had not yet gotten to the interchange of the 5 and 14 freeways. Caltrans has since finished that retrofitting of overpasses. In response to a different type of failure in the 10 Freeway over La Cienega Boulevard, Caltrans has redesigned expansion joints.

Another area of progress is a fix for quake motion breaking gas lines in homes. Since Northridge, connections have included an valve that automatically shuts during a quake, Although many failure modes were known to engineers prior to the Northridge quake, it was a surprise to discover that in some steel-framed skyscrapers, welds had cracked and failed.

Previously, it was assumed the weld was stronger than the steel beams, which were designed to flex and bend during strong shaking. After the Northridge Quake, Los Angeles ordered inspections of the welds in steel-framed buildings near the epicenter, but not skyscrapers in areas of the city south of the Hollywood Hills, including downtown LA.

What's more, some engineering models indicate that under certain conditions, strong enough shaking could bring down a steel-framed structure even if the welds held up.

"It's conceivable that in large enough shaking, downtown may lose some of its tall buildings," Heaton said.

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