Case study of Base Isolation System: The U.S. Court of Appeals Building in San Francisco

                 Research has established the FPS system as a well understood and effective seismic isolation system. As a result, the FPS system was selected for seismic retrofitting of the U.S. Court of Appeals Building in San Francisco.

                  The U.S. Court Building in San Francisco is an early example of American Renaissance style and is the only such example in the western United States. Constructed in 1905, it features granite exterior walls, marbles columns and statues, hand painted murals and mosaic tiles floors. The building has plan dimensions of 95m by 81m and overall height of 25m above the street levels. It consists of full basement, four floors and two mezzanines. Its weight is approximately 57000 metric tons.

                   The Court house survive the great 1906 San Francisco earthquake, but was damaged in 1989 Loma Prieta earthquake. Damaged to the interior tile walls, which formed part of the lateral load resisting system. Significantly reduced its seismic resistance. The buildings owners, the General Services Administration, closed the building while investigating retrofitting methods. Seismic isolation was selected over conventional retrofitting schemes because it afforded the greatest degree of seismic protection had the least impact on the buildings historic and architectural character and had the least lifecycle cost.

                    The FPS system was selected based on the cost and technical merit. The technical reasons for selecting the FPS system were:

The extensive series of test performed upon the FPS system

It could be installed with minimal alteration of existing foundation.

It would minimize transmission of over turning moment.

It would not require additional reinforcement of the buildings footing.

     The installation of the isolation system was completed in July 1994. it consist of 256 FPS bearings, having a radius of curvature of 1880mm and displacement capacity of 350mm. Eight different bearings types carry load in the range of 450 to 5350 KN.

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