Resonant behaviour of base-isolated high-rise buildings under long-period ground motions

The resonant behaviour of base-isolated high-rise buildings under long-period ground motions is investigated. The long-period ground motions are known to be induced by surface waves. While the acceleration amplitude of such long-period ground motion is small, the velocity amplitude is fairly large. It is expected that high-rise buildings and base-isolated buildings with long fundamental natural periods are greatly influenced by these long-period ground motions. Especially base-isolated high-rise buildings with friction-type bearings may have remarkable mechanical characteristics unfavourable for these long-period ground motions. The purpose of this paper is to reveal that the long-period ground motions recorded in Japan have the intensity to make base-isolated high-rise buildings in resonance with long-period components and that careful treatment is inevitable in the structural design of these base-isolated high-rise buildings. It is pointed out that the friction-type bearings are effective in general in avoiding the resonance with ground motions with a narrow-range frequency characteristic, but are dangerous for ground motions with a wide-range frequency characteristic in the long period range.