Can SF earthquakes topple these buildings? Here's when we'll know

Sep 06, 2023

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This concrete building at 2 North Point Street has undergone seismic upgrades, though many San Francisco concrete buildings have not — a source of concern to city officials.

Outside the Maxine Hall Health Center on Pierce Street, colorful panels cover a concrete sheer wall that was added as part of seismic upgrade two years ago. Many other concrete buildings in the city have not been retrofitted for earthquakes.

When will San Franciscans be able to know whether their office or apartment buildings are at risk in a major earthquake?

The city does keep a list, published last month by NBC News, of 3,400 buildings believed to be concrete that could be at risk of collapsing in a major earthquake.

Concrete buildings could account for 50% of deaths in a 1906-size earthquake in San Francisco, according to a 2010 city-commissioned study. They are one of the most significant kinds of buildings yet to be retrofitted for earthquake safety in San Francisco and are located on nearly every block in downtown, the Tenderloin and Chinatown.

But city officials and structural engineers caution that this list is preliminary and inaccurate — which is why The Chronicle is not publishing it.

A better list will come, according to Brian Strong, director of the city's Office of Resilience and Capital Planning, only after the Board of Supervisors passes a seismic retrofit ordinance for concrete buildings, which city staff are currently developing and plan to have before the board by the beginning of next year.

"We can't compel property owners to give us information on their buildings without going to the Board of Supervisors," Strong said.

The prior list, Strong said, was compiled by "volunteers or by the city working with interns and so forth" — by people who walked around the city eyeballing which buildings were concrete combined with the use of fire insurance maps, property tax data and Google maps.

It's inaccurate because some of the buildings on the list (such as the Ferry Building) are actually primarily made of steel, and it doesn't account for buildings that have been retrofitted or may have been torn down, Strong said.

The only way to verify a building's vulnerability is to consult a structural engineer, Strong said.

Supervisor Myrna Melgar said she has been in contact with Strong and would support an ordinance on seismic retrofits for concrete buildings. She plans to schedule a hearing on the issue in September.

"The city needs to come up with a list that is (accurate). People who live in those buildings have the right to know," Melgar said.

The city is focused on a class of concrete buildings known as non-ductile concrete, which means they lack sufficient steel bar reinforcement to prevent structures from continuing to crack and potentially collapse. Non-ductile concrete buildings were built primarily before the 1980s, when building codes were strengthened after damage was observed in these kinds of buildings in earthquakes across the world.

Non-ductile concrete buildings suffered significant damage in the February Turkey-Syria earthquake, with some of these buildings’ floors collapsing into each other, a phenomenon known as "pancaking."

The risks that non-ductile concrete buildings pose have been known for decades, but many cities have prioritized retrofit programs for less complicated, less expensive building hazards. Santa Monica, West Hollywood and Los Angeles have passed retrofit requirements, with deadlines for retrofits varying from 10 to 25 years.

San Francisco began exploring a retrofit ordinance for concrete buildings in October, focusing on buildings built before 1995 because "we’re very confident that after ’95, they’ve been addressed" by building codes, Strong said.

Strong said that to get an accurate list of buildings that need retrofits, if the Board of Supervisors decide to pass a concrete building retrofit ordinance next year, the first step would be to reach out to building owners on the preliminary list and require them to fill out building information sheets and contract a structural engineer to evaluate the building.

"We’re not talking about a heavy lift. We’re talking about something that's not going to be very expensive to do, in the hundreds of dollars in most situations," Strong said.

Melgar, however, said the Department of Building Inspection already has the authority to conduct inspections of multifamily buildings without needing board approval and could do so to shore up the city's existing list of potentially vulnerable concrete buildings.

"Why haven't we done it before then?" Melgar said. "I will certainly ask that question during the hearing."

In an email to The Chronicle, Department of Building Inspection spokesperson Patrick Hannan wrote that the agency doesn't have the authority, staff or funding to conduct structural assessments necessary for seismic retrofits.

San Francisco underwent a similar process for a different class of vulnerable buildings, known as soft-story, in 2013. The city started with a preliminary list of 7,000 suspected soft-story buildings, but after an ordinance was passed, that list was whittled to 4,900 buildings — because some buildings had already done retrofits, been torn down or weren't soft-story after all, Strong said. The final list and the status of each building's retrofit was then published online, and 90% of required soft-story retrofits have been completed, according to Strong.

Right now, Strong's team is having meetings with building owners, tenant groups, labor, nonprofit housing developers and neighborhood business associations, after which they’ll put together a set of recommendations for the mayor and Board of Supervisors.

Strong said there are no details finalized about the timetable of concrete retrofits and what would be required. It is likely that buildings will be split into different tiers, with the most vulnerable — in terms of occupancy and how the building is used — requiring retrofits the soonest, he said.

Non-ductile concrete seismic retrofits can be complicated, as they are typically more invasive and expensive than other retrofits. People living or working in affected buildings might have to relocate while retrofits are being done.

"We know this is going to be more difficult for people that are in vulnerable populations, people on rent control. We’re going to need to try to find different ways to help pay for some of the costs or other things that can help make it more feasible," Strong said.

The push for concrete building retrofits in California began in Los Angeles in the early 2010s, after UC Berkeley architecture Professor Mary Comerio created a list of non-ductile concrete buildings for the city as part of a research grant from the National Science Foundation to understand the risk of such buildings. Her team had approached both Los Angeles and San Francisco in 2007 asking to do a case study — the former said yes, the latter no, she said.

Her team used field visits and over a dozen data sources to compile Los Angeles's list, which she said had an error rate of about 7% and is "much more accurate" than the list for San Francisco that is now public.

The Los Angeles Times acquired Comerio's list of almost 1,500 buildings with a public records request and published it — leading to a team of scientists creating a set of recommendations for earthquake safety, and ultimately, the City of Los Angeles adopting all the recommendations in an unanimous ordinance. As of 2019, the Los Angeles list has been pared down to more than 1,300 buildings, and none had completed a retrofit under the new ordinance.

To Comerio, it showed that public attention and political will could lead to sweeping improvements in earthquake safety. But now, she's worried that expensive seismic retrofits for concrete buildings could be hard to pass given San Francisco's budget shortfalls and emptying downtown, with some buildings owners already in financial crisis.

"We are in economically difficult times … but we still have a responsibility to keep people safe. I think we need to advance this project a little bit faster," Melgar said.

Structural engineer René Vignos, chief operating officer at the engineering firm Forell Elsesser, is hopeful that there will finally be enough political will to move forward retrofits on this decades-old problem in San Francisco.

He sees the publication of San Francisco's preliminary list as a double-edged sword — though it could cause fear among people who don't need to worry about their building, it also creates more awareness around the vulnerability of concrete buildings to collapse.

"Engineers don't often get this moment where people are listening, and so we have to take it when it comes," Vignos said.

Reach Claire Hao: [email protected]; Twitter: @clairehao_