ESTIMATION OF STRONG GROUND MOTION AND BUILDING DAMAGE IN THE 1995 HYOGO-KEN NANBU EARTHQUAKE

摘要

Much strong-earthquake data was recorded during the Hyogo-ken Nanbu Earthquake, but little was recorded for Chuo-ku, Nada-ku, Higashi-nada-ku, Ashiya-shi, and Nishinomiya-shi areas, where many buildings suffered severe damage. In this study, we simulated strong-earthquake motion for these areas and then determined the correlation between seismic level and building damage. We simulated the strong-earthquake motion in the Sannomiya district in Chuo-ku by using a two-dimensional FEM (finite element method) soil model that included an observation point. The simulation results show that ground motion at the surface of Osaka-strata had peak acceleration exceeding 800cm/sec~2 and a peak velocity exceeding 120cm/sec, away from the Suwayama fault. The area where these maximum values occurred was 600m wide. The result also shows that the Motoyama-strata had a peak acceleration of 837cm/sec~2 and a peak velocity of 145cm/sec. For both the Sannomiya and Motoyama districts, the seismic intensity level derived from the simulated ground motion corresponds well to the areas of concentrated damage. We also simulated the earthquake response of an eight-story reinforced concrete building (in Motoyama) whose actual damage included a collapsed first-story. The simulation results show that the maximum story-deformation angles for the upper second-story were about 2.7/100, compared with 1/200-1/50 estimated from the actual damaged building. When the maximum input acceleration was 'decreased to 60% of the simulated ground motion, the maximum story-deformation angle was about 1/200, and when decreased to 70%, the angle was slightly greater than 1/100. When this acceleration exceeded 70%, the deformation angle of the first story was significantly larger than for the other stories. To simulate the building-damage level by using earthquake-response analysis, the input acceleration must be decreased to 70-80% from simulated ground-surface motion. This phenomenon may be caused by the interaction between the building and ground.