In a Global First, 181 Fremont in San Francisco Awarded New Earthquake-Resilience Rating
SAN FRANCISCO, CA Arup and Jay Paul Company announce that 181 Fremont (the third tallest structure in San Francisco, California) has achieved a REDi Gold Rating, which will make it the most resilient tall building on the west coast of the U.S. when completed. The 56-story, mixed-use tower, built above five basement levels, is being constructed in compliance with a new set of holistic design and planning guidelines the Resilience-based Earthquake Design Initiative (REDi Rating System) that allow it to withstand the impact of a 475-year seismic event (roughly a M7.5-M8.0 earthquake on the San Andreas Fault) with minimal disruption.
Arup developed REDi with contributions from a diverse group of external collaborators. The system outlines holistic design and planning criteria within a resilience-based framework for architects and engineers to enable owners to resume business operations and provide livable conditions for tenants quickly after an earthquake. This goes beyond the building code's "life safety" approach which is intended to allow building occupants to exit the building safely but does not consider a building's functionality or even reparability.
"We sought to develop a blueprint for designers and owners who wanted to achieve higher resilience targets, with the ultimate intention to promote community resilience. This aligns with Arup's mission to shape a better world," said Ibrahim Almufti, SE, LEED AP, the leader of the development team for the REDi Rating System and Project Manager for 181 Fremont.
As part of the design verification for REDi, Arup has also developed a methodology to predict the downtime of an organization whose buildings have been damaged by earthquakes. This has been utilized to estimate seismic risk for owners, hospitals, academic institutions, and corporations.
For 181 Fremont, Arup served as the structural engineer, geotechnical engineer, and resilience consultant on the project, shepherding the design team and owner through the resilience-based design process. This involved critical engagement with the developer Jay Paul Company, architect Heller Manus Architects, other engineering consultants, and the contractor Level 10. The owners and designers pursued a REDi Gold Rating which included enhanced structural and non-structural design to limit damage, improved egress systems, contingency plans to reduce post-earthquake recovery times, and development of a tenant's resilience manual of recommendations to keep their space earthquake-ready.
These design measures helped reduce the expected repair costs by approximately 10 times compared to a code-designed building and in conjunction with contingency planning, reduces the expected functionality downtime from 18 months to less than a few weeks. As the structural engineer, Arup developed innovative design solutions to achieve these objectives, including the incorporation of viscous dampers (similar to vehicle shock absorbers) within the steel megabraces and uplifting megacolumns to significantly reduce the potential for earthquake damage. Not only do these measures significantly reduce seismic forces and wind vibrations, they also resulted in material savings of approximately 3,000 tons of steel and allowed the removal of a tuned mass roof damper (the common technology to mitigate wind vibrations for occupant comfort) which freed up the entire penthouse floor for occupancy.
The design of 181 Fremont was subject to a rigorous seismic peer review process required by the city of San Francisco, including review of Arup's advanced earthquake computer simulations of the tower. An additional voluntary peer review was pursued by Jay Paul Company to ensure that the design complied with the REDiscriteria. The additional review was conducted by Professor Greg Deierlein of Stanford University who approved that the design satisfied the criteria to achieve a REDiâ„¢ Gold Rating. And in another important sign of industry acceptance, the USGBC has developed new Resilient Design Pilot Credits for the LEED Rating System which reference REDi by name.