Comparison of US and Japanese Codes and Practices for Seismically Isolated Buildings

The number of base isolated building in Asian countries, especially Japan, far outstrips the number in the United States. Base isolated buildings in Japan number in the thousands while the number in the U.S. remains around one hundred. Unlike its use in Japan, isolation technology in the U.S. has remained within mainly essential, public buildings such as hospitals, city halls or 911 centers. The technology has not spread to use in typical office or residential buildings, which may also see increased safety and performance benefits. This paper compares the codes and practices for designing seismically isolated buildings in the U.S. and Japan. The design spectra are developed for buildings of the same occupancy rating located in comparable seismic regions in both countries. The design process is discussed from determining the ground motion demands through peer review and isolation device testing. Special attention is made to the code design methods for isolated building in the two countries with focus on the displacement demands for isolation devices. A comparison of the displacement demands for a three-story office building is made.