181 Fremont Tower is a mixed-use tower in San Francisco’s high-density Transbay corridor of the South of Market district.  

The project is the third tallest building in the city, rising 800ft above street level with 56 stories, including five basement levels. Arup provided structural and geotechnical services and assessed the potential impact of the 181 Fremont Tower on the adjacent Transbay Transit Center during large earthquakes.

Arup’s geotechnical team derived the geotechnical properties of the soils and bedrock and proposed recommendations for the temporary and permanent works of the project, including design of the drilled shafts, base mat, shoring walls, and basement walls. The geotechnical team also provided services during construction, including monitoring of the showing wall and adjacent structures during the deep basement excavation.

The project was awarded two ‘Best in Category’ accolades from the Council on Tall Buildings and Urban Habitat’s Annual Awards, for both geotechnical and structural engineering.

Ibbi Almufti
Ibrahim Almufti, from Arup’s San Francisco office, spoke about the resilience-based design of 181 Fremont, the third tallest high-rise in San Francisco.

Ground engineering

Arup’s geoseismic services included site-specific earthquake hazard and ground motion development, advanced soil-structure interaction analysis to beneficially reduce the earthquake demands due to embedded basements, and advanced structure-soil-structure interaction to prove that the performance of the tower does not adversely affect the performance of the Transbay Transit Center.

Seismic design

As the West Coast of the United States’ most resilient building, Arup’s structural engineers employed a holistic resilience-based seismic design approach to minimise damage during an earthquake and allow people to return to the building after a seismic event, far exceeding building code criteria. Its iconic tapering form, small footprint and location inside the Transbay urban regeneration zone presented significant engineering challenges.

We incorporated groundbreaking design solutions, including an innovative viscous damping system within the architecturally expressed steel mega-braces and uplifting mega-columns to significantly reduce seismic and wind demands. This resulted in a steel material saving of approximately 3,000 tons.