An overview of some of the skyscrapers in the SoMA neighborhood on Thursday, May 10, 2018. (Kevin N. Hume/S.F. Examiner)

Seismic report on existing tall buildings recommends re-inspection

A first of its kind study of tall buildings in San Francisco released Thursday recommended the re-inspection of buildings with a specific type of steel construction, which was found to be problematic after the 1994 Northridge earthquake.

The Tall Buildings Safety Strategy report, which included 15 other safety recommendations to reduce seismic risk, was commissioned by the late Mayor Ed Lee after news emerged that the Millennium Tower was sinking.

“We want to make sure there is trust in government, trust in our regulators,” said City Administrator Naomi Kelly. “That’s why Mayor Lee asked us to reach out to academics and engineers” – specifically ones that had not worked on tall construction projects in San Francisco, and who therefore wouldn’t have a conflict of interest.

“This is one of the first efforts, I think, to really look back and start to be proactive about starting to look more carefully at assessing those buildings,” said Greg Deierlein, an engineering professor at Stanford and one of the study’s authors.

“San Francisco has one of the most stringent building codes in the country, and we are always looking at how to improve those codes,” Kelly said. “What’s different now is we’re looking at existing buildings.”

Supervisor Aaron Peskin, whose district includes many of the tall buildings in San Francisco, said a hearing about the report’s findings will be held before the Government Audit and Oversight Committee on Oct. 17 – which by chance happens to be the 29th anniversary of the Loma Prieta earthquake.

The completion of the report was “no small feat,” Peskin said, and that a similar effort was scuttled over a decade ago, which “I attribute to some of the building interests in San Francisco.”

While the report made no attempt to prioritize its 16 recommendations, Peskin said he considered the highest priority to be its recommendation to re-inspect buildings that used “welded steel moment frames.” Those structures use a specific type of weld, which only after the 1994 Northridge earthquake in Los Angeles was discovered to be susceptible to fracture.

Following the Loma Prieta earthquake, tall buildings in San Francisco were re-inspected, but engineers at the time were not aware of the potential problems steel moment frames face.

The report created a database to study 156 buildings in San Francisco taller than 240 feet, primarily located in the northeast parts of The City.

“Prior to the creation of this database, the City had no centralized, searchable repository with this information about all tall buildings in its jurisdiction,” the report said. “Following the completion of this project, The City will need to develop a mechanism for maintaining or expanding the database.”

The report recommends the database be expanded to cover all buildings higher than 75 feet or on sites susceptible to liquefaction. The 240-foot height the report used was “somewhat arbitrary,” it said.

“It’s kind of mind-blowing that in the technology era none of this information existed in one place,” Peskin said.

Some of the report’s recommendations would need to be implemented by regulation through the Department of Building Inspection, Peskin said, but others could be enacted by legislation through the Board of Supervisors.

“My job is to keep this in the public mind and create political willpower to have it done, because none of these things happen overnight,” he said. “They take years, and decades.”

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