True or false: The building codes in San Francisco were radically revised after the 1906 earthquake to improve the strength and safety of all new buildings.
True, right? Actually, no. It's true that there were good intentions to improve the fire and safety codes. But as UC Berkeley's Bancroft Library's online exhibition "The 1906 San Francisco Earthquake and Fire" notes: "In fact, the building code changed very little in the aftermath of the earthquake and fire."
According to the book "Denial of Disaster: The Untold Story and Photographs of the San Francisco Earthquake and Fire of 1906," not only were the defects in earthquake and fire resistance repeated in the rebuilding, but "building code standards were actually reduced from those in effect before the Great Fire."
How did that happen?
Not surprisingly, there were political and commercial pressures to get on with rebuilding, and it's easy to sympathize with the survivors' sense of urgency. Almost 5 square miles of the city lay in ruins, and tens of millions of dollars in insurance claims (back when a buck was worth more than $20 in today's money) were pouring into the city. In other words: Codes, schmodes, let's get building!
Realizing that the vast destruction cast a pall on both prospects and property values, business leaders quickly grasped the wisdom of excising "earthquake" from their pronouncements, replacing it with the less frightening (and more insurance-worthy) "Great Fire" of 1906. (The insurance companies typically paid out property loss claims for fire losses, not for earthquake damage.)
Indeed, "Denial of Disaster" states that just days after the earthquake, The Chronicle reported that the Real Estate Board resolved that the phrase "the great earthquake" would hitherto be known as "the great fire."
Partly as a result of this downplaying, seismic safety did not play as large a role in the rebuilding as one might expect. The primary focus was less "pre-quake" mitigation (improving building and fire codes) than "post-quake" preparedness (establishing a more robust system of water supply for firefighting).
Although San Francisco did adopt a new building code in 1909 (after much of the city was already rebuilt or under construction), seismic safety lay largely dormant until the 1933 Long Beach quake destroyed many unreinforced masonry schools. Classes were not in session at the time of the quake, but the prospect of children being crushed by collapsing brick walls motivated the Legislature to pass the Field Act and Riley Act, which effectively banned brick buildings.
Subsequent San Francisco building code overhauls in 1939, 1956, 1975, 1984, 1990 and 1992 greatly advanced building and fire safety. And even though a San Francisco program mandated strengthening of unreinforced masonry, or URM, buildings in 1986, which has worked through about 90 percent of the city's nearly 2,000 brick buildings, legacies of the 1906 quake and fire remain. There are still thousands of hastily rebuilt unreinforced masonry buildings cheek-by-jowl with wooden structures with no fire-resistant walls between them.
In addition, hundreds of "soft-story" multifamily dwellings, built before 1939 when codes were significantly strengthened, are at risk of first-floor collapse. Soft-story buildings typically have large openings on the ground floor for garages, storefronts or windows that make them more likely to collapse or be damaged in an earthquake.
Also, recent earthquakes in Los Angeles, Loma Prieta and Kobe, Japan, revealed unexpected risks posed by "non-ductile" concrete buildings built before 1976. Non-ductile means a rigid or inflexible frame or building.
Taken together, these are powerful reminders that improved building codes alone cannot guarantee the structural integrity of homes, shops and workplaces in an '06-size disaster.
Limitations of any code
The more one learns about the complexities of righting these risks, the more grateful one becomes that we have structural engineers, architects, builders, officials and politicians -- yes, politicians -- to deal with the mind-numbing difficulties of setting seismic standards and policies.
The complexities of researching and codifying advances have engendered a byzantine overlay of agencies and jurisdictions with a say in code formulation and adoption: City, state, county and federal agencies have areas of authority. The much-maligned Federal Emergency Management Agency, for instance, funded a painstaking study of how to strengthen old buildings, resulting in comprehensive guidelines for the seismic rehabilitation of existing buildings -- a key advance in the field.
Engineers and building officials face these challenges:
-- No building is quake-proof in the sense of suffering zero damage. The goal of most designs is what's called "life safety," protecting the lives of occupants, and limiting damage.
-- Modern codes don't address existing buildings until the buildings are modified or renovated.
-- Codes are rulebooks, and like all rulebooks, they contain trade-offs. There are no guarantees, only reductions of risk.
-- Quake knowledge accumulates sporadically over time.
-- A code is only as good as its enforcement and a building's maintenance.
-- There are only so many resources available, and these have to be balanced between "pre-quake" mitigation of risks and "post-quake" response and recovery.
Structural engineer Patrick Buscovich, who's had a hand in strengthening hundreds of San Franciso's hazardous brick buildings, uses his own seismically retrofitted house in Noe Valley as an example of risk reduction. "You're going to have damage in a major earthquake," he says. "The goal is to minimize the damage so you can still live there after the quake."
As one of three engineers tasked by the city to inspect and red-tag (mark as unsafe for occupancy) buildings in the Marina district after the 1989 quake, Buscovich says that people underestimate the post-quake difficulties created by unsafe housing.
"Sleeping on a friend's sofa gets old after about a week," Buscovich says. "The reality is, if your house is severely damaged, it may take years to get it rebuilt. People in Kobe were still living in government trailers years after the quake." Being able to sleep in your own bed, he says, is often the best argument for why people should invest the money to retrofit their homes.
Fellow engineer David Bonowitz, who chairs a code recommendation committee on existing buildings for the Structural Engineers Association of Northern California, says that all codes imply specific performance objectives. "Identify a risk, quantify it, and mitigate it -- that's the procedure," he says. "The first goal is to prevent death during an earthquake. But beyond life safety, is the building designed to be usable 24 hours after the quake? Or is it designed to even be repairable? That's the next issue. Getting that extra performance from older buildings is rare."
Buildings built to recent codes, Bonowitz says, are designed for reliable performance in a quake. But current codes don't require property owners to retrofit or strengthen older buildings until triggered by a remodel. And each municipality deals with the issue of older buildings in its own way. Sixteen people died in a soft-story complex in the 1994 Northridge quake. In the 2003 San Simeon quake, two people were killed in Paso Robles when a historic and unretrofitted brick building failed. So the risk is hardly theoretical.
Cities can mandate retroactive fixes, Bonowitz says, requiring owners of old buildings to bring their properties up to newer standards. But such mitigation requires a balancing act between public safety and the costs to building owners and the disruption of businesses. Owners are often reluctant to invest in life safety seismic upgrades because these measures are not seen as protecting the value of the property itself.
There are no quick-fix solutions or easy trade-offs, Bonowitz notes: "The problem was decades in the making, and it will take decades to solve."
According to Chief Building Inspector Laurence Kornfield (one of four city CBIs), San Francisco has already mandated two such seismic risk-reduction programs. A 1969 ordinance required owners to strengthen, remove or replace parapet walls, cornices, chimneys and other architectural features that tend to fall off in a quake and kill people below.
(As Chronicle architect columnist Arrol Gellner has noted, this is the basis of an apocryphal story in which a correspondent wires from a quake zone, "Buildings are fine, but all the architecture fell off." The San Francisco fire chief was killed in the 1906 quake by just such a cornice toppling from an adjacent building.)
Kornfield says the parapet work was completed as part of the 1986 unreinforced masonry strengthening before the Loma Prieta quake, saving many lives as a result. Barring such specific mitigation programs, however, if a building is left in its original state, no seismic strengthening is required. Renovations or additions trigger upgrading, and Kornfield says the city was fortunate that the dot-com boom led to many such upgrades of older buildings. But the rate of voluntary upgrading, Kornfield reports, especially by owners of multifamily buildings, is low.
The city is in the midst of a comprehensive citywide risk assessment study, and Kornfield says "preliminary results seem to indicate that wood-framed, "soft-story" buildings, especially corner buildings, are one of a number of building types that could have a major impact on San Francisco if seriously damaged in an earthquake." The loss of such key buildings would affect affordable housing, small businesses, and the architectural and cultural fabric of the city.
Soft-story multifamily buildings that could collapse in a quake are especially hazardous when businesses like restaurants and stores occupy the first floor.
"When these buildings collapsed in the Marina in 1989, they crushed parked cars" in first-floor garages, Buscovich says. "But in areas like the Sunset and Richmond districts, these buildings could kill people who happen to be having a meal or shopping."
Is it worth the property owners' money and inconvenience to small businesses to mandate hundreds of these multifamily wooden structures be brought up to a newer, stronger seismic safety code? Buscovich says that doing nothing could trigger a widespread loss of the city's character. "If we lose these key neighborhood buildings in the next earthquake, we lose both affordable housing and small businesses," he says. "What will replace them? Maybe it'll be condominiums."
Buscovich says the city should require owners to retrofit the highest-risk structures -- older soft-story multifamily buildings sited on poor soil. "The engineering community is saying, 'We know some buildings will perform poorly in an earthquake.' We have a moral obligation to let everyone know the levels of risk posed by these building types and soil conditions."
A careful survey, Buscovich says, will enable the city to select the buildings most at risk and to set standards that will produce a big cost-benefit payoff. "Maybe we don't need to fix every old multistory wood-frame building, but if we don't tackle the highest-risk ones, we risk losing our neighborhoods."
Codes aren't enough
Modern building codes are based on widely adopted "model codes" drawn up under careful scrutiny by national organizations. The most familiar is the Uniform Building Code, but the International Existing Building Code is also gaining acceptance in many jurisdictions.
Such standardized codes are fine for new construction, but San Francisco must deal with thousands of existing buildings, many of which predate the '06 fire or were quickly rebuilt shortly afterward. To take but one example, consider fire escapes. Kornfield says they were banned by the Uniform Building Code, but allowed by San Francisco. Why?
"We have many buildings without side exits because another building is pushed right against the exterior walls. How else can you get people out of such constricted spaces? Fire escapes have worked well for us for over 100 years."
Codes are "prescriptive," which means that they're designed as recipes that can be applied to every building of a certain type. The alternative is to engineer each building by calculating the loads, soil type and so on. Clearly, this takes more time and money than following a set of rules. But a code, like any recipe, has limitations.
A structure near Russian Hill, for instance, might survive a quake intact while an identical building South of Market might suffer near-collapse. The difference? The soil beneath the buildings. In one infamous example of what can happen on filled-in marsh or bayshore, the Valencia Street Hotel was four stories before the '06 quake rumbled through, and only one story shortly thereafter; three stories sank into the unstable fill as it liquefied, killing an estimated 100 residents.
"Not many people know that there was once a marshy lake the size of three city blocks in the middle of the Mission District," Buscovich says. "You could reach it by boat from the bay, via Mission Creek. If you overlay maps of the '06 and Loma Prieta quake damage, you'll find they're remarkably similar. The filled-in marshes, creeks and bayshore areas remain inherently riskier than other parts of the city."
The irony, Buscovich says, is that the city celebrated the rebuilding of the Embarcadero, South of Market and Mission districts, which were destroyed in 1906, by filling in more of the bay and building the 1915 Pan-Pacific Exposition on precisely the same sort of filled-in land that had contributed to such destruction in 1906. This filled-in land, of course, became the Marina district.
"While the city built the Expo on wooden pilings, they sold off the land after the Expo was demolished without requiring similar pilings," Buscovich says. "And so we had the same building failures and fires in 1989 in the Marina as we had South of Market in 1906."
Since major earthquakes are rare, engineers and scientists do not have many opportunities to study how buildings actually perform in a quake. Every quake provides insight into how buildings respond. As the unexpected structural failures in the Loma Prieta (1989), Northridge (1994) and Kobe (1995) earthquakes revealed, there is still much to learn. As a result, even a building that complies with '70s-era codes may fail.
Dan Shapiro, who has logged more than 50 years as a structural engineer, puts it simply: "We learn from our mistakes." The problem, he says, is that the "input motions" -- the way the earth moves in a quake -- are difficult to measure. Back in the '06 era, before seismology was a field of study, Shapiro says, engineers reckoned that earthquakes generated lateral stresses, much like wind.
It was only after the 1933 quake in Long Beach that engineers focused on shaking and how buildings overturn. It wasn't until the 1970s that a real understanding of how buildings perform in an earthquake was developed; the structural failures that occurred in recent quakes alerted engineers to subtler risks posed by poorly inspected weld joints between steel beams and posts, and the placement of reinforcing steel rods within concrete posts and beams. As a result, even relatively modern concrete structures built in the '50s, '60s and early '70s may be at more risk of failure than previously estimated.
Shapiro, a member of the State Seismic Safety Commission since 1996, helped develop the FEMA-backed guidelines for seismically rehabilitating existing buildings. While the guidelines established a methodology for strengthening "super-hazardous" unreinforced masonry structures, there is plenty more to be done.
"The field is constantly evolving," Shapiro says. "Even modern buildings should be looked at to see what can be done to make them safer."
Shapiro has this advice for homeowners: "There are so many things you can do to make your house safer, from bolting and bracing foundation walls to securing water heaters and tall bookshelves. Even small improvements in safety can make a big difference."
Bancroft Library's online exhibition, "The 1906 San Francisco Earthquake and Fire": bancroft.berkeley.edu/collections/earthquakeandfire/exhibit/.
California Seismic Safety Commission: www.seismic.ca.gov.
Structural Engineers Association of Northern California: Lessons learned in the five most significant earthquakes, www.seaonc.org. Also, lessons from the 1906 quake: www.celebratingeqsafety.com/1906-earthquake.
"Denial of Disaster: The Untold Story and Photographs of the San Francisco Earthquake and Fire of 1906," by Gladys Hansen and Emmet Condon (Cameron & Co., 1989). Hansen served as archivist for San Francisco; Condon, as fire chief.
"A Dangerous Place: California's Unsettling Fate," by Marc Reisner (Pantheon, 2004).
Earthquake retrofitting for homeowners, 10 a.m.-5 p.m. July 8. Instructors are engineer Tony DeMascole and contractor Jim Gillett; $75, Building Education Center, 812 Page St., Berkeley; (510) 525-7610; www.bldgeductr.org.