West
The French Market
SGH provided fire life safety and accessibility consulting services to assess the original French Market building and identify conditions that may need to be addressed as part of the planned renovation project.
San Francisco, CA
Millennium Tower, 301 Mission Street
Scope/Solutions
With bedrock more than 200 ft below street level, the fifty-eight‑story tower at 301 Mission Street, like most downtown high rises, is founded on piles driven through soft, compressible clay soils deposited by the San Francisco Bay and extending into a dense sand layer overlying ancient marine deposits of clays, silts, and sands. Consolidation and lateral displacement of the soils under the building’s weight and adjacent construction activity caused the tower to settle more than 17 in. and tilt 17 in. across its footprint, concerning the condominium owners and City of San Francisco. SGH assessed the effects of this movement on the building’s stability and earthquake resistance, and designed an upgrade to arrest further settlement and reverse much of the tilting.
As part of our assessment, SGH evaluated whether the building required structural reinforcement to restore its integrity or seismic resistance to original design levels. Highlights of our work include:
- Developing detailed nonlinear models of the structure, its foundations, and underlying soil to simulate the effects of settlement and tilting
- Conducting detailed nonlinear analyses of the structure’s response to earthquake shaking
- Designing an underpinning retrofit for the structure, consisting of jacking approximately 10% of the building’s weight onto eighteen new foundation piles
extended to rock along the structure’s north and west sides
Although our analyses demonstrated the building retained the earthquake resistance intended by the building code and would even after additional settlement, the owners argued this reduced their units’ value. The retrofit, which arrests future settlement and reverses tilting over time, helps assure them the problem is addressed and that the building is safe and serviceable.
Photo by iStock / Sundry Photography
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Project Summary
100M
Construction Value
Award
Winner
Solutions
Failure Investigation | Repair & Rehabilitation
Services
Structures | Advanced Analysis
Markets
Commercial | Residential
Client(s)
Millennium Partners | Paul Hastings LLP
Specialized Capabilities
Geotechnical | Computational Mechanics | Failure Analysis
Key team members
Additional Projects
West
Williams-Sonoma at Union Square
Once known as Bullock & Jones men’s clothier, this 18,000 sq ft cast-in-place concrete building was reconstructed after the 1906 San Francisco earthquake. Williams-Sonoma wanted to create a dramatic effect with a new central atrium, which required major modifications to the existing structure.