The plywood is used to support the cripple wall after it is bolted to the frame. Plywood is remarkably strong and flexible, making it an ideal reinforcement for seismic retrofits.
Researchers at UC Berkeley Tuesday presented the city of LA with a list of older concrete buildings that could be at risk of collapse during a major earthquake.
KPCC's Frank Stoltze says it'll help determine which structures may need seismic retrofitting and prevent a lot of deaths.
For months researchers delayed releasing the list. They said their work was preliminary and they worried about legal liability.
Now, after discussions with city officials, UC researchers have delivered the addresses of nearly 15,000 hundred buildings constructed before 1976 and made of stiff concrete frames, which wouldn't bend easily during an earthquake.
But researchers say the list doesn't identify buildings that are specifically at risk of collapse, but rather the types of buildings that could be vulnerable. Mayor Eric Garcetti echoed that point Tuesday.
"The list is going to have some buildings that they said they're not sure, but they think may be more vulnerable in an earthquake."
The list includes more than 200 schools and hospitals, for example, many of which have been required by law to be retrofitted. City officials declined to release the addresses to KPCC, but a publicly available version shows the bulk of the structures--more than 700--are industrial, commercial or office buildings. There are 65 parking structure and 47 hotels.
The mayor said the city intends to review the list closely as part of efforts to improve earthquake safety and he's brought on Dr. Lucy Jones to look at precisely that as part of a one-year process.
Jones of the United States Geological Survey is perhaps the preeminent expert on Southern California earthquakes, and Garcetti's new earthquake czar. Jones said it's likely that only a fraction of structures on the list would collapse during an earthquake.
"I think need to not make too much of the list."
Jones says engineers have estimated that around 10 percent of these types of buildings could crumble during an earthquake. The next task for the city is to ask property owners if they've upgraded their buildings or know of structural features that make them safe.
"Any of the buildings at risk are from a time before digital databases so we're talking about paper records and how (to) sift through all that and understand it is a big issue."
And city resources are scarce. Luke Zamperini, Chief Inspector for the LA City Department of Building and Safety, says his agency has no funding for the inspection of these buildings. Many, perhaps hundreds will require physical inspection, Jones says.
The mere release of the list is an important step toward making the city safer during earthquakes, says John Wallace, a professor at UCLA's Department of Civil and Environmental Engineering.
Significant not just because of the list, but because there's 20 years of research in how to make concrete buildings safer at lower cost.