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Charm and Risk in San Francisco

As the 1906 quake centennial nears, experts say the city's distinctive architecture leaves it vulnerable in the face of another major temblor.

January 08, 2006|Sharon Bernstein | Times Staff Writer

SAN FRANCISCO — Laurence Kornfield's favorite San Francisco bar is a wood-framed tavern with floor-to-ceiling windows wrapped around a street corner in the South of Market neighborhood, with apartments stacked on top of it.

It's a typical San Francisco streetscape, one that gives the city much of its flavor -- and much of its risk in case of a serious earthquake.

"The lower floor would be squished," Kornfield, chief building inspector for this city of 740,000, said as he looked at the bar.

With the city set to commemorate in April the 100th anniversary of the devastating earthquake and fire of 1906, seismic experts and structural engineers say San Francisco could be devastated again by a major temblor despite a century of improved building design and firefighting expertise.

Much of the problem involves the very architectural styles that give the city its charm.

In contrast to Los Angeles, where most people live in low-slung housing that tends to hold up well in earthquakes, San Francisco is a much denser city and has a far higher percentage of residential structures that experts worry could fail in a big quake.

A 2003 assessment of quake-vulnerable buildings in San Francisco concluded that as much as 35% of the city's private buildings -- and up to 70% of its wooden housing -- could be lost to fire or quake. All told, about 45,000 out of a total of 122,000 buildings are at risk, the assessment concluded.

"I can walk you around town and point out buildings that ... there's not a chance in hell they're going to stand up," said Patrick Buscovich, one of the city's leading structural engineers. "You can't walk a city block without seeing them."

Experts now say San Francisco has three major types of buildings of concern:

* The classic block-long attached retail spaces with apartments above them that are commonly seen downtown and in other retail districts are vulnerable to collapse because the bottom floors have many windows and few strong walls. Experts are especially worried about shop fronts at the ends of blocks, where plate-glass windows wrap around corners, depriving structures of needed support.

* Single-family homes built over garages to accommodate the city's many hillsides and take advantage of its dramatic views are at risk because the garage often lacks sufficient support to hold up the rest of the house during heavy shaking.

* Many of the city's trademark high-end apartment and condominium buildings -- including several on Nob Hill and Russian Hill and in other exclusive neighborhoods -- are made of concrete, with little or no steel bracing. These structures, called non-ductile concrete buildings, could crack during a major quake and then pancake.

It's not that the structures were poorly built; most developers have adhered carefully to the codes in effect when the buildings were designed, Buscovich said. But with each new quake, scientists learn more about how buildings respond to shaking ground. Because of newer codes, many structures that were considered safe just a few years ago could not be built today.

Two destructive temblors in the last decade taught seismic lessons that have prompted concerns about San Francisco.

The 1994 Northridge quake and the one that shook Kobe, Japan, a year later both showed that "soft first story" structures -- those with weakly reinforced garages, lobbies or other open spaces on the first floor -- are more susceptible to collapse than scientists and structural engineers had believed.

Some San Francisco owners of such properties have begun taking it upon themselves to retrofit their buildings, even though city regulations don't require it.

George Orbelian, who owns and manages apartment and office buildings throughout the city, said all of his properties have been evaluated for earthquake hazards.

One, an 11-unit apartment building in Buena Vista Heights that he managed until it was sold recently, had been built right up to the edge of a cliff over a large, open garage with no back wall. The garage ceiling -- above which sat several floors of apartments -- was held up in the middle with a single steel post, 10 inches in diameter and hollow in the middle.

Reinforcing the garage with massive steel beams dug into the earth cost $200,000, but Orbelian said it was worth it.

"I didn't want to take a chance on someone getting hurt," he said.

Kornfield, the chief building inspector, has been trying on his own to develop an inexpensive way of shoring up the ubiquitous bottom-floor garages.

With volunteer help, he has outfitted an empty industrial space with a pair of archways holding typical garage doors. On weekends, he and a team of engineers, carpenters and developer friends experiment with bracing, steel wire and other techniques for strengthening doors and walls. The materials cost only a few dollars at the hardware store.

"It doesn't take much," Kornfield said, tinkering with a cable. "It hardly takes anything to keep a building from collapsing."

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