San Francisco's sinking Millennium Tower could withstand a major earthquake

Dive Brief:

A report funded by the city of San Francisco has found that despite its sinking and leaning, the 58-story Millennium Tower could withstand a magnitude 8.0 earthquake, according to the San Francisco Chronicle.
The new report's findings echo those from a study that developers paid for last year. The city, however, decided to conduct its own analysis after some residents of the luxury tower, which has sunk 16 inches since its 2009 opening and now leans to the northwest, said they did not trust the results.
While the city-appointed engineers said the building is safe for now from significant damage due to seismic activity and other structural dangers, they suggest ongoing observation of the structure and additional future assessments.

Dive Insight:

The tower's plight has been a saga for San Francisco since officials discovered the high-rise was sinking more than the four to six inches that had been projected for its entire lifespan. Engineers may have found a way to stabilize and reset the building, but that process would come at a cost of $100 million to $150 million.

While engineers try to correct the structural tilting and sinking issues, this latest city report marks good news for residents and neighbors who were skeptical about how the building would hold up during a significant earthquake. With researchers having tested the structure for an 8.0 magnitude earthquake, Millennium's condo owners should have an added layer of assurance, given that the biggest recorded San Francisco earthquake registered a 7.8 more than a century ago, according to National Geographic.

Seismic activity is a concern and design consideration for any new construction project in California. Tall buildings, in particular, have a different seismic response than other structures, according to the Pacific Earthquake Engineering Research Center (PEERC). To assure proper performance during an earthquake, PEERC makes recommendations spanning from the geotechnical and seismic ground motion phases through to design. Those include a maximum considered earthquake evaluation and a baseline for the development and integration of building code provisions for tall buildings.

While there have been many recommendations put forth for West Coast developers, San Francisco's building codes don’t require the vast majority of its buildings to be retrofitted to protect against earthquake damage. The city recently enacted legislation requiring owners of almost 2,000 apartment buildings — wood-frame structures of five to 15 units — to bring them up to current seismic safety measures.

Los Angeles has also embarked on a comprehensive retrofit program requiring the renovation of approximately 15,000 buildings to comply with seismic regulations.