Aisladores sismicos

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Journal of Japan Association for Earthquake Engineering, Vol. 4, No. 3(Special Issue), 2004

POST-KOBE APPROACH FOR DESIGN AND CONSTRUCTION OF BASE-ISOLATED BUILDNGS
Masayoshi NAKASHIMA1, Peng PAN1, Dan ZAMFIRESCU2, and Ruediger WEITZMANN1
Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto Japan, nakashima@archi.kyoto-u.ac.jp 2 Technical University of CivilEngineering Bucharest, Bucharest 72302, Romania ABSTRACT: Japan has two decades of experience in designing and constructing baseisolated building structures. Construction has increased significantly since the 1995 Hyogoken-Nanbu (Kobe) earthquake, having reached over 150 annual construction projects. Many new developments and refinements have been made in the material, device, design, and construction ofthese structures. This paper summarizes recent design and construction of base-isolated building structures in Japan, including statistical data with respect to the common usage as well as the number of new projects. Key Words: base-isolation, buildings, bearings, dampers, seismic design, peer-review
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INTRODUCTION The concept of modern seismic base-isolation emerged in the early 1970s in NewZealand (Skinner et al 1993). As in other earthquake-prone developed countries, the application of base-isolation in Japan began in the early 1980s (the first building was finished in 1983). The start was slow and until 1985 only three demonstration projects were completed. During the 1985-1994 period, during the Japanese economic boom, the number of base-isolated buildings began to increase,reaching about ten buildings per year (Fig.1), and Japan became a leading country in the number of base-isolated buildings. Design was characterized by a very large scatter in the main design parameters and in the choice of isolation devices.
1000 Number of buildings 800 600 400 200 0 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000

Fig. 1 Isolated buildings until 2001 (Building 1990-2002; Report2002) After the 1995 Kobe earthquake a new era began for seismically isolated buildings in Japan

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(Fig.1) (Building 1990-2002; Report 2002). The number of base-isolated buildings significantly increased to more than 150 buildings per year. Seismic isolation moved from the experimental stage to the mass production stage, characterized by relatively standard detailing and devices.Clark et al. (2000) reasoned that the explosion of base-isolation applications was caused by the devastating human and economic losses that led a search for alternatives to traditional seismic design approaches. The observed damage to buildings also produced a sense of doubt regarding the reliability of traditional construction approaches particularly concerning damage protection of the structure andits contents. This paper reviews the state-of-the-practice of Japanese design and construction of seismically isolated buildings to share with the readers the experience and knowledge accumulated in this field over the last 20 years.
other 11% apartment facilities
other 29% 44% apartment facilities 2% computer center

laboratories 24%

28%

4% houses 24% office building 9% computer centerlaboratories 3% office building

17% 5% houses

Before 1995

After 1995

(a)

(b)

Fig. 2 Types of facilities (Report 2002)

CONSTRUCTION STATISTICS The built floor area, an important index of the development in practical application, recorded a leap after 1995 and continued to increase slowly in more recent years. The main reason is the increase in the building height; theaverage number of stories rose from four to five stories before 1995 to about eight stories after. Before 1995, many base-isolated buildings were relatively small buildings including laboratories, experimental offices, and dormitories built and owned for demonstration purposes by construction companies. Funding for these buildings typically came from construction companies’ research investments, and...
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