Executive Summary

The 1995 Kobe earthquake shook two seismic isolated buildings, both of which were located approximately 30 km from the epicenter. These two buildings, the Matsumura-Gumi Research Laboratory and the West Japan Postal Savings Computer Center (West-1), performed very well, though they were outside the region of strongest shaking. The West-1 building was, at the time, the largest seismic isolated building in the world. Both buildings were instrumented, and experienced ground accelerations of approximately 0.3g. Accelerations were reduced to 0.1g in the West-1 superstructure. Prior to the Kobe earthquake, no building with passive structural control in Japan had experienced a significant earthquake. The number of isolated and passively damped * buildings built, or being built, has increased markedly since the January 17, 1995 Kobe earthquake. From 15 isolated buildings approved in the three years before the earthquake, construction approvals increased to more than 450 in the three years since. The authors suggest that this increase is due to the fact that seismic isolation technology had become relatively mature at about the time of the earthquake. The devastating human and economic losses in that event spurred society to look for alternatives to traditional seismic design approaches.

To synthesize a diverse cross-section of viewpoints, the authors conducted a written survey of about 150 designers, owners, and researchers. They also visited a number of building sites, design offices, and research facilities in Japan. The 30-question survey covered:

  • General issues
  • Project-specific information
  • Design process
  • Owner requirements and economics
  • Regulatory and approval issues
  • Future trends

This case study illustrates the marked increase in buildings that employ seismic isolation and passive energy dissipation in Japan. It identifies the technical, economic, political, and cultural factors that contributed to this trend. It provides an example of how being in the right place at the right time can lead to broad changes in practice in a short period of time. A window of opportunity to educate the public opened. The public was receptive to learning the basics about seismic design and the newest approaches for earthquake protection, and the media and the construction and development industries provided information. The survey results provide a broad perspective on the implementation of isolation technologies in the wake of the Kobe earthquake. Comparisons are made with practices and trends in the United States.

* References to passive damping are restricted to distributed energy dissipation devices and do not include tuned passive control technologies such as tuned mass dampers and sloshing liquid dampers.