San Francisco Chronicle Article-Soft Story buildings at risk in quake
Published Thursday, December 11, 2008
Without a seismic retrofit, 80 percent of San Francisco’s weakest wood-frame buildings are expected to collapse or to suffer damage beyond repair in the large earthquake scientists say will hit the city within decades. Results from an ongoing seismic safety study show that 2,800 wood-frame buildings that house nearly 60,000 residents and 7,000 employees would sustain $4 billion in damage. Retrofits, the study estimates, would dramatically reduce the damage but could cost more than $130,000 per property. That’s far from the only damage the city would see in a large temblor. So far, the city-funded study has focused on less than 10 percent of the city’s residential units that are believed to be seismically unsafe. The “soft-story” structure is the classic San Francisco apartment building with a store or restaurant on the first floor. It gets its name from a ground-floor space – a window or garage door – situated where a wall might otherwise be. San Francisco has more of those buildings than any other Bay Area city, and they are made more precarious by neighborhoods perched on unstable soil. The open space makes the frames prone to twisting and buckling, and many of the buildings were damaged in the Marina district in the 1989 Loma Prieta earthquake and in Southern California during the Northridge earthquake in 1994. The initial study results announced Wednesday are part of the city’s first endeavor to fully understand the health, safety and economic risk posed by the city’s buildings during a major earthquake. The work factored in a temblor of magnitude 6.9 (Loma Prieta) to 7.9 (1906 quake).
Soft Story Investigation abandoned
The city commissioned an investigation of vulnerable buildings in 2000, but abruptly and inexplicably abandoned it three years later. The study project was later restarted this summer (2008) by the city’s Department of Buiding Inspection. A Chronicle report in June highlighted the fact that the city had no strategy for fixing the structures despite the fact that the danger had been known for decades. In July, 2008, Mayor Gavin Newsom directed city departments and earthquake consultants to focus their analysis on the soft-story structures and to develop retrofit guidelines for them by the end of January 2009. He also introduced legislation that he said would make it easier and cheaper for building owners to retrofit properties by cutting the cost and time of obtaining building permits. At the time, Newsom said he did not feel that it was necessary to require building owners to seismically shore up their buildings as other Bay Area cities have done.
Newsom’s legislation later was killed by a committee of the Board of Supervisors, and some of the members complained that there was no proof that any building owner would actually take advantage of the program. Very few privately owned buildings in the city have been retrofitted. Newsom seems willing to change his mind about requiring the work. In an e-mail Wednesday, Newsom spokesman Nathan Ballard said, “A consensus seems to be emerging that a mandatory program is likely to be recommended. The mayor is certainly open to argument, and he will make a policy decision after he thoroughly reviews the recommendations.”
Earthquake experts said the study demonstrated that the soft-story structures represent a tremendous risk to the city. “The analysis shows that these buildings are extremely vulnerable to earthquakes, and it’s really an issue the city needs to face,” said Laura Samant, a seismic engineering consultant leading the project. “Thousands of people would need shelter, and this is just looking at one class of buildings.” Some local engineers have estimated that the city has more than 5,500 soft-story buildings, which house approximately 80,000 residents.
The study focused on the city’s 2,800 wood-frame buildings that have three or more stories and five or more units and “significant” ground-floor openings. It ignored another 2,800 multistory wood-frame buildings that don’t have large openings on the ground floor, as well as buildings with fewer stories – such as the homes built over garages, common in the Sunset District.
The study will continue for at least another year and a half and will examine other building types. Earthquake consultants who convened at a city-sponsored workshop Wednesday said the wood-frame buildings could be made much safer with retrofits that would cost between $71,000 and $132,000, depending on the materials used and the amount of work.
Common methods are adding plywood shear walls, steel frames and columns. Surveys indicate that most of the vulnerable soft-story buildings are located in five neighborhoods: the Western Addition, the Mission, the Richmond, the Marina and North Beach. Consultants presenting information at the workshop said that under state law, landlords are allowed to pass on 10 percent of a tenant’s rent in perpetuity to pay for the cost of a retrofit, even if they are in a rent-controlled unit – of which the city has 180,000.
Quake erases rent control
Conversely, if a rent-controlled building destroyed in an earthquake is replaced, its units are no longer subject to rent control. Because retrofits would occur mostly on ground floors, businesses likely would be displaced for several months during the construction, consultants said. In the coming months, earthquake engineers and several city departments will review recommendations relating to retrofits – whether they should be voluntary or mandatory and how rigorous they should be – and send them to Newsom.
“We think people are going to need more than a whisper to get them to do this,” said Laurence Kornfield, San Francisco’s chief building inspector. “There will need to be some kind of action to require them to do it along with some help, financial or otherwise.”
Quake danger to buildings
A new study on earthquake dangers in San Francisco focuses on the weakest of all buildings – wood-frame structures with a window or garage where there might otherwise be a solid wall. The initial study focused on 2,800 of those structures that are three floors or higher and have at least five housing units. It factored in a quake of a magnitude between 6.9 and 7.9. The study found that:
Extent: 80 percent of those buildings would collapse or be destroyed beyond repair.
Residents: 58,000 residents live in the buildings.
Businesses: 2,100 businesses are situated in those buildings.
Workers: 6,900 people work in such buildings.
Damage: A major quake would cause $4 billion in damage to those buildings.
Source: Community Action Plan for Seismic Safety “