Ujnr Workshop on Soil - Structure Interaction

This report reviews the soil-structure interaction (SSI) researches relating to three major earthquakes recently occurred in Japan, which include the 1993 Kushiro-oki earthquake, aftershocks of the 1993 Hokkaido-Nansei-oki earthquake and the 1995 Hyogo-ken Nanbu earthquake. The review work is focussed on the simulation analyses conducted on the basis of simultaneous earthquake records observed both in buildings and in the surrounding soil during these major earthquakes, as well as other small events observed at the site. One of the most interesting results reviewed in this report is the ratio of response spectra for the observed motions in a building to those for motions recorded on the soil surface. Marked difference of the ratios for small ground motions and for the strong motions in the Kushiro-oki earthquake is detected. It is also discussed that the nonlinear response analyses conducted with use of the two-dimensional FEM for soil-structure system have resulted in considerable deviation from the observations during the strong motions in the Kushiro-oki earthquake. Regarding the Hyogo-ken Nanbu earthquake, on the other hand, satisfactory results of the simulation analyses are overviewed. Furthermore, special emphasis is placed on a study of effective input motions into structures investigated on the basis of the simultaneous observations recorded both in structures and the surrounding soil during the Hyogo-ken Nanbu earthquake. The compared results of the peak values recorded on the foundation with those on the free-field soil surface indicate distinctly the reduction of effective input motions into structure. The effective input rates, which indicate the ratios of peak values of the effective input motion to the corresponding free-field motion, are approximately 0.7 for accelerations and 0.9 for velocities. In addition to the topics, a general trend of SSI researches for the last ten years in Japan is overviewed.