Durability of Rubber Isolators by Long-Duration Ground Motion Due to Large Earthquakes

Abstract eng:
In Japan, the Tokai earthquake and the Tonankai earthquake are expected to occur in the near future. Due to these earthquakes, the possibility of suffering from a big shake is pointed out in the big city around the Pacific Ocean coast. It is expected that the vibration continues for a long time especially in high rise buildings and seismic isolated buildings with a long natural period. The response displacement of seismic isolated building become greater than the design displacement, and the re-verification of the energy dissipation capacity of isolation devices is required. In this research, the dynamic experiments of lead rubber bearings (LRB) and high damping rubber bearings (HDR) carried out to verify the energy absorption capacity. In the experiments, the repetition of 200 cycles or more and the maximum shear strain of 200% was examined (the total loading time is 600 seconds). The maximum temperature of the center of HDR (LRB) specimen reached over 80 (100) Celsius in accumulated displacement about 70m. The hysteretic characteristics were changing in the experiment along with the repetition (remarkably decrease in the yield force and the equivalent stiffness), and it was clarified that the energy dissipation capacity was decreasing as the temperature increasing. The characteristics of the specimen almost returned to the initial state after the temperature had decreased. The influence that the change in these hysteretic characteristics gave to the maximum response in seismic isolated building was verified by the response analysis. As the results, it was shown that it was important to evaluate the change in the hysteretic characteristics of isolation devices appropriately.

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