“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.
Yet nearly a quarter of a century later, California is still wrestling with what to do with the hundreds of buildings, many of them high rises, that were constructed during the more than three decades when the defective connection system was widely employed. Last year Santa Monica, which has identified more than 70 steel-frame buildings believed to have the problem, became the first city in California to order mandatory retrofits. A similar law in nearby West Hollywood comes into effect in August.
“This is an issue that structural engineers should have been dealing with continuously since the mid-1990s and we just dropped it,” said Keith Porter, an earthquake engineering expert who helped lead the United States Geological Survey study that published the list of San Francisco high rises. “We don’t know how to deal with a problem this big.”
A few towering notables that made the unfortunate list: Salesforce West; 555 California, partially owned by President Donald Trump; Transamerica Pyramid; 101 California; and the love-it-or-loathe-it San Francisco Marriott.
Here are the buildings at risk:
8. Pacific Gas and Electric Building, 77 Beale
17. California Automobile Association Building, 100 Van Ness [Update: The New York Times issued a correction for 100 Van Ness, noting, “The owners of one of the buildings, a 20-story building at 100 Van Ness Street, reached out to disclose that the building had undergone a comprehensive renovation that brought the building up to code and thus made it more seismically safe.”]
19. Spear Tower (One Market Plaza)
20. Steuart Tower (One Market Plaza)
37. Hilton San Francisco Hotel, 333 O’Farrell
San Francisco isn’t the only city in need of major work before the next high-seismic quake. Roughly 9,000 soft-story buildings in Los Angeles still need comprehensive earthquake retrofits.
Silver lining: This is an excellent reminder to get prepared for the next big earthquake, which could happen any day now.
Update: A spokesperson representing the investors/owners of 100 Van Ness replied with the following statement care of Kevin Menninger, S.E., principal-incCharge at Nishkian Menninger:
The renovation project at 100 Van Ness, from 2013-2014, brought the 1974 structure into full compliance with the 2013 structural code. The renovation required non-linear dynamic analysis as well as physical testing to ensure the existing structure, which included pre-Northridge moment frames, would withstand the maximum credible earthquake without damage to the existing beam-to-column joints. The original precast-concrete cladding system and the 2 level mechanical penthouse including massive equipment were removed which helped reduce the seismic weight by over 30%. The heavy precast concrete exterior walls were replaced with significantly lighter state of the art glass curtain system. With the significant reduction in weight, the existing Welded Unreinforced Flange moment frame system was found, through extensive analysis and weld testing, to provide the structural performance to meet the 2013 code. The analysis and testing of the structure were reviewed by the City and County of San Francisco Department of Building Inspection and Professor Ted Zsutty PhD, an internationally recognized seismic engineering expert, who both have validated the integrity of this structure. This renovation received a Structural Engineers of California Excellence in Engineering award in 2016 as well as national recognition from Engineering News Record.