Quake exposed buildings’ weaknesses

Little has been done since 1989 to protect thousands of vulnerable residential buildings that were built like those that fatally crashed and burned in the Marina district during the Loma Prieta earthquake.

Pushes to mandate seismic retrofitting of so-called soft-story buildings have failed, leaving about one-third of San Franciscans living in the dangerous structures and The City at risk of losing rent-controlled apartments.

A soft-story building is wood-framed with above ground-level garages or shops that are structurally weaker than the upper stories and prone to crumble in an earthquake.

Seven such buildings collapsed into the soft sand and landfill of the Marina district after Loma Prieta struck — six of them on corner lots.

Soft-story buildings on corner lots are especially vulnerable to collapse if their ground stories contain garage openings or storefronts on two walls instead of one.

Another 65 of the neighborhood’s 1,400 soft-story buildings were damaged moderately or severely, studies found.

The Department of Building Inspection and nonprofit think-tank San Francisco Planning and Urban Research Association have both recommended that The City force property owners to reinforce their soft-story buildings to protect residents during earthquakes. Such legislation, however, has not been drafted or introduced.

Lawmakers are scheduled to consider legislation by Mayor Gavin Newsom that would instead cut some city fees and expedite permit approvals for retrofit projects to encourage property owners to shore up their soft-story buildings.

The old age of San Francisco’s soft-story buildings, combined with rent-control laws that limit rent increases in pre-1980 buildings, creates policy challenges for lawmakers who want to protect their constituents from earthquakes, according to SPUR executive director Gabriel Metcalf.

“The vulnerable buildings are older buildings,” Metcalf said. “If they’re rental apartment buildings, then that means they’re under rent control, so the revenue streams may not be there to support borrowing the money needed to retrofit the buildings.”

Under state law, rent control doesn’t apply to new buildings built to replace those demolished in an earthquake. That means San Francisco could be unaffordable for hordes of renters after an earthquake.

It costs between $5,000 and $20,000 to retrofit a soft-story building, according to Department of Building Inspection Director Vivian Day. DBI is estimating that roughly 10 percent of the owners of the thousands of soft-story buildings will voluntarily reinforce their properties.

In a move to help building owners retrofit their soft-story buildings, DBI is pursuing federal grants and investigating whether unused money raised through bond-sales to reinforce buildings across The City can be given or loaned to property owners.

Prone to collapse

Soft-story buildings are multistory, wood-framed residential buildings without inside walls in their lower stories, making them likely to fail in the event of an earthquake.

60,000 Soft-story buildings in The City needing retrofits
43 to 85 percent Proportion expected to be unsafe after 7.2-magnitude quake
11 to 21 percent Proportion expected to collapse after 7.2-magnitude quake
7 Collapsed soft-story buildings
in Marina after Loma Prieta
4 Soft-story buildings in Marina destroyed by fire after Loma Prieta
4 People who died in Marina after Loma Prieta

Source: S.F. Department of Building Inspection

Majority of city’s masonry edifices reinforced

After five people were crushed to death by rubble following the collapse of a building facade in the South of Market neighborhood during the 1989 earthquake, most similar brick buildings in San Francisco were shored up to prevent such deadly incidents.

The top-floor facade of a four-story building at Sixth and Bluxome streets tore away from the building as the ground beneath it was rocked by the Loma Prieta earthquake, which fatally dumped tons of bricks on car occupants and pedestrians below.

The building was one of 1,700 unreinforced masonry buildings that dotted The City before the quake struck, Department of Building Inspection figures show.

Since 1989, 1,432 of the 1,700 unsafe brick buildings have been retrofitted to protect them during earthquakes and 93 have been demolished, DBI figures show.

That leaves 175 dangerous unreinforced buildings in The City, the figures show.

DBI Executive Director Vivian Day credited the high retrofit rate with city and state laws that mandate safety improvements to unreinforced masonry buildings and a voter-approved bond sale that loaned retrofit funds to property owners.

Nonprofits and faith groups in brick office buildings and churches have had the most difficulty complying with the regulations, according to Day.

“Lots of nonprofits out there have had a tough time raising the money,” she said.

Falling hazards

Unreinforced masonry buildings are brick buildings that are vulnerable to serious earthquake damage.

1,700 unreinforced masonry buildings in The City in 1989
1,432 retrofitted since 1989
93 demolished since 1989
175 remaining

Source: S.F. Department of Building Inspection


For The Examiner's complete Loma Prieta anniversary coverage, go to http://www.sfexaminer.com/loma-prieta/

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