City expert panel says Millennium Tower meets seismic criteria but long‑term settlement and fix remain unresolved

An expert panel convened by the City of San Francisco told the Government Accountability and Oversight Committee on Aug. 1 that, based on available analyses, the 301 Mission Street tower known as Millennium Tower meets the city's seismic performance criteria for a maximum considered earthquake, but long‑term settlement and what a definitive structural fix would require remain unresolved.

"Based on the analyses we reviewed, 301 Mission is safe in the event of a maximum considered earthquake," said Professor Greg Deierlein, a civil and earthquake engineering professor who led the city's expert engineering panel. He said updated modeling by Simpson Gumpertz & Heger (SGH) shows the building's expected seismic story drift (about 2.2 percent) is below the Administrative Bulletin 83 threshold of 3 percent.

The panel’s review, Deierlein said, relied on SGH’s finite‑element and nonlinear "Perform" modeling and on documents including the SGH ("Hamburger") reports from 2014, 2016 and 2017. Deierlein cautioned that the panel did not independently re‑survey raw settlement measurements and that evaluating future settlement scenarios and causes was outside the panel’s contracted scope. "We did not verify the original surveys," he said.

Supervisor Aaron Peskin, who called the…