The 39 San Francisco high-rises at risk of collapse during a major quake, according to the U.S. Geological Survey

From Curbed San Francisco:

“Most of the structures, which were built between 1964 to 1994, are clustered around downtown, the Financial District, and SoMa” 

The U.S. Geological Survey released a gasp-inducing report regarding the structural security of dozens of San Francisco high-rises that could be in peril when the next major earthquake strikes.

New York Times reporter Thomas Fuller sifted through the USGS report to reveal the nearly 40 buildings in SF that could buckle following powerful earthquakes, like the one that hit San Francisco in 1906.

Most of the structures, which were built between 1964 to 1994, are clustered around downtown, the Financial District, and SoMa. The reason for concern: Many of the skyscrapers employed the use of a flawed technique that wasn’t remedied until after a major Southern California earthquake in the 1990s.

The faulty technique, known as welded steel moment-frame buildings, fuses together columns and beams rather than using the pricey and time-consuming bolts and rivets method, which was used in steel frame building in previous generations.

While the building code with said technique was rewritten following the Northridge quake, many of the buildings constructed using the welded steel moment-frame system have yet to be retrofitted.

According to the New York Times:

Engineers have known about a major defect in certain steel-frame buildings since 1994, when shaking from the Northridge earthquake in Los Angeles fractured critical joints in more than 60 buildings, bringing at least one very close to collapse. The building code was rewritten to eliminate the flawed technique....

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