Seismic Analysis of a Low-Rise Base-Isolated Structural System

A base-isolation system was developed for earthquake protection of low-rise structures. The system incorporates spherical supports for the base, a specially designed spring-cam system to keep the base supported under normal conditions, and moves for the duration of the earthquake under the constraint of a spring with optimized stiffness characteristics. The dynamic behaviour of a three-story concrete structure with and without the base isolation subjected to the Taft and El Centro earthquake loads was investigated. The results indicated that the absolute peak acceleration and displacement as well as shear forces decreased significantly with the application of a base isolation system, and it is possible to achieve 87 to 94% reduction in the maximum accelerations and transmitted forces. The movement of the base relative to the ground was less than 0.15 m in the optimized system, and the springs were not fully compressed at any time during application of the earthquake loads. The maximum induced vertical forces as a result of the spherical base support were found to be less than 1.5 % of the weight of the structure. Since the system performance is highly dependent on the rapid unlocking of the cams in the event of a seismic disturbance, careful consideration should be given to the optimal design of the spring-cam system.

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