New Guidelines for High-rise Foundations in San Francisco

Millennium Tower in San Francisco - Image Vanguard Properties

The 645-foot tall Millennium Tower in San Francisco settled an incredible 16 inches, and tilted at least 2 inches to the northwest.  Recently the City and County Department of Building Inspection (DBI) issued interim guidelines and procedures for structural, geotechnical and seismic-hazard engineering design review for new buildings over 240 feet tall.  The guidelines, available from the Department of Building Inspection, have requirements for buildings 240 feet or higher and are located in the City’s “softest soils and/or liquefaction zones, as defined by the california Seismic Hazard maps.”

These buildings will need to have two geotechnical reviewers on the Engineering Design Review team unless the project has piles or drilled piers anchored into bedrock, in which case they can have one reviewer.  Additionally, all of these buildings will require the Project Sponsor to contract with qualified Monitoring Surveyors and Instrumentation Engineers (MSIEs)” to monitor the settlement of the buildings and foundations of the project for 10 years after completion.  They will submit a legal document every year containing the monitoring results that will be recorded against the building’s title.  If the settlement exceeds the geotechnical designer’s predicted settlement by a factor of 1.5, the DBI Deputy Director has to be notified.

Source:  ENR, Get the document at the DBI; Image: Business Insider

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