U.S. Court of Appeals – Structural Engineering
Constructed in 1905, San Francisco's U.S. Court of Appeals Building survived two major earthquakes during the 20th century (in 1906 and 1989). Following the 1989 Loma Prieta earthquake, which significantly damaged the Beaux Arts building, the General Services Administration hired SOM to seismically upgrade the structure. It was the federal government's first base isolation seismic retrofit project, and the world's largest such project at the time.
SOM's evaluation focused on three issues: where to locate the plane of isolation, which system to use, and the amount of strengthening required. Based on the study of a complex matrix incorporating functionality and cost considerations, SOM selected a plane of isolation just above the foundation. The team employed a Friction Pendulum Isolation System (FPS), resulting in savings of $4 million.
Lifting existing columns for placement of the FPS isolators was especially challenging given the building's weight and historic brittle finishes. SOM used concrete jacking blocks to raise the fragile steel columns. This time-efficient and technically innovative approach had never been used in the world. A total of 256 bearings were installed in six months.