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San Francisco Issues Rules for Foundations

Monday, December 18, 2017

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In light of San Francisco's sinking tower saga—in which the Millennium Tower condominium building has sunk and tilted several inches—the city and county Department of Building Inspection has released guidelines for design review for buildings that are 240 feet or taller.

The guidelines, which cover procedures for geotechnical, structural and seismic-hazard engineering design review, were released on Nov. 9, and apply to all tall buildings, whether they were designed using the city's prescriptive code or performance-based design.

City Guidelines

According to Engineering News-Record, the guidelines require an additional member or two for a building’s peer-review panel. These members can either be a state-registered geotechnical engineer or a civil engineer with proven geotechnical experience. Projects located in at-risk areas—where the soil is subject to liquefaction or is in a seismic zone—would require an additional geotechnical engineer on the team.

Hydrogen Iodide, public domain, via Wikimedia Commons

In light of San Francisco's sinking tower saga—in which Millennium Tower has sunk and tilted several inches—the city and county Department of Building Inspection has released guidelines for design review for buildings that are 240 feet or taller.

Before a project is completed, sponsors must hire the appropriate personnel, such as monitoring surveyors and instrumentation engineers, to monitor the settlement of the building and foundation of the structure for 10 years after completion. Monitoring also entails an annual report to the city.

Another guideline requirement is that the peer reviewer must meet with the engineer-of-record and the building inspection staff and submit a report once the review is completed. The report must cover 10 areas, including: the design of the building's shallow and/or deep foundation systems; geological site hazards; and effects of dewatering, among others.

According to the News-Record, cost for the building sponsor, and whether all buildings must be equipped with sensors to monitor settlement remains unclear.

The Sinking Saga Continues

According to an engineering report from the Arup Group, the rate of sinking remains steady at Millennium Tower. There have also been new cracks continuing to form in the basement, noted the Chronicle.

“It’s approximately the same rate of sinking and tilting as before,” said one source.

When the Chronicle reached out to P.J. Johnston, spokesperson for Millennium Partners, he declined to comment on the talks or the findings of the latest engineering report, but said that for Millennium Partners, the priority has always been the building.

“We’ve been working closely with the [homeowners’ association] throughout the mediation process, and we’re optimistic that we’ll reach an agreement on the fix,” Johnston said. “To do so, it’s imperative that we respect the confidentiality of the mediation process. Any proposed solutions are preliminary until an agreement is reached.”

Jack Gallagher, a spokesperson for the San Francisco city administrator’s office, told the Chronicle that no repair plan had yet been submitted to the city for repair permits. Bill Strawn, spokesperson for the Department of Building Inspection, noted that his own office had just recently received the latest engineering report, which the department had passed on to the city’s data engineers for their review.

Previous Problems

Millennium Tower’s other recent problems include an ongoing odor problem, which was indicative of gaps in the walls of at least one unit. Upon investigation, it was discovered that these gaps were not protected by the appropriate fire-resistant caulking.

An investigation conducted by the city in January concluded that the tower is safe to live in, but the fact remains: The structure is still sinking at a rate of two inches per year, double what was originally estimated by engineers, according to The Associated Press.   

Millennium Partners has largely blamed the Transbay Joint Powers Authority for disturbing the tower while building its Transbay Transit Center on an adjacent lot. Others argue the blame lies with the developer. Multiple lawsuits have been filed in relation to the matter.

   

Tagged categories: Architecture; Condominiums/High-Rise Residential; Government; Health and safety

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