by Abigail Sterling and Brian Hackney
SAN FRANCISCO (KPIX 5) — We probably won’t know for months exactly what caused the deadly condo collapse in Surfside, Florida. What we do know is that it was an older concrete multi-story building. San Francisco has a lot of them. And some have been a safety concern for years for different reasons – specifically earthquakes.READ MORE: Downsized But Not Out, Dreamforce Conference Set to Boost Business in San Francisco
Concrete highrises built before 1980 are most at risk. KPIX has discovered the city already has compiled a list of buildings that will have to get inspected. And many may have to get retrofitted.
On February 9, 1971, the magnitude 6.5 San Fernando earthquake in the suburbs of Los Angeles was one big surprise that day. The other surprise – brand new buildings like the Sylmar hospital collapsed. It was a new, but brittle, concrete building.
In Mexico City a few years later, same thing happened. Then in Northridge in 1994 and, most recently, Christchurch, New Zealand in 2011.
“Same thing, over and over and over again over the years,” said Peter Yanev, a longtime structural engineer.
And San Francisco? The city is packed with thousands of old concrete buildings at risk of collapse in a big quake.
“Well the old ones didn’t have enough reinforcing steel and we’re looking here on the roof. Quite a few of those buildings didn’t have enough steel, so they’re really not ductile,” said Yanev. “After a big quake, we will likely, unless we fix them, have a number of large building collapses.”
“Well think of the [double-decker Interstate Highway 880] Cypress structure during the 1989 [Loma Prieta] earthquake, that would have been non-ductile concrete,” said Skip Walker, an independent building inspector. “In San Francisco, you’ll see city blocks where that’s almost all there is, these older, non ductile concrete buildings.”
It’s a problem the city has been aware of since that day in 1971. “It was a seminal moment for California. We changed all of our codes in response to [the San Fernando] earthquake,” said Brian Strong, San Francisco’s Chief Resiliency Officer. “Right now we do have vulnerable concrete or what we would call low ductility concrete buildings in San Francisco.”
But here’s what we don’t have: a program to actually inspect them and – if found to be defective – make them safer. In fact, 50 years on, we don’t exactly know how many there even are, a problem Yanev characterized as “pretty big.”
“We know there are around 2,700 or so concrete buildings that were built before 1990,” said Strong. “The city identified about 3,200 buildings that fit their criteria,” said Walker.
Fifty years on, the city has finally identified and mapped 3,700 concrete buildings, with help from the Structural Engineers Association of Northern California.READ MORE: Flames Reach Ancient Sequoias; Crews in Pitched Battle to Save Giant Forest Grove
“What we are looking at when we look at this inventory is the building occupancy,” said the association’s president Emily Guglielmo. “If it’s a multi-family high density unit, those are structures we want to pay particular close attention to.”
Many of the buildings are concentrated in areas of high-rise apartments and downtown commercial centers. “All the building owners will receive a letter that says you are part of this program and you will have a certain timeframe to bring an engineer in to complete this checklist,” said Guglielmo.
The city gave us a map crowded with dots, but no addresses. Despite repeated requests from KPIX 5, the city is sitting on the list of buildings that has not been made public. One possible reason: “The money that we’re talking about is huge,” said Walker.
Yanev concurred that retrofitting such buildings will be expensive.
“Now we know that the buildings are unsafe, at least many of them, they need to be looked at, analyzed to determine the cost/benefit and then some decisions, some hard decisions will have to be made,” said Yanev.
“It wouldn’t make sense for us to ask every property owner that has a concrete building to conduct an expensive evaluation of their building,” said Strong.
But in Los Angeles where all this began, the city has implemented a mandatory inspection and retrofit ordinance. They’ve identified older buildings that are possibly at seismic risk, inspected them and when necessary, ordered retrofits.
San Francisco has only finally taken the first step, which is to identify suspect buildings. But it still has not decided what to do with information that perhaps hundreds of thousands of people might be living or working in collapse hazards.
“I don’t think we’ve made that decision yet,” said Strong.
“You know what the problem is, you know how to fix it. We need to apply the resources to start making that happen,” said Walker. “We can kick the can down the road, obviously for a long time. But that’s the wrong approach because there will be a day of reckoning on this, there will.”
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