Abstract
Abstract
This paper analyses a case study of the dynamic behaviour of structures with a base-isolation device support. The objective of the present analysis is to understand why and under what conditions the base-isolation pair is effective in reducing earthquake-induced forces in structures. To this end, a one-storey building with high-damping rubber bearings (HDR) installed between the base building and the foundation was considered. Most isolation systems are non-linear in force-deformation relations, but this behaviour was not considered, since, in the region of typical design rubber shear strain (100 per cent), the rubber shear modulus does not change sharply, and thus the isolator shows approximately a linear behaviour. In order to evaluate the efficiency of the base-isolation system under earthquake motion, linear analysis using a modal superposition technique was carried out on buildings with and without the isolation system under two different strong ground motions, namely the Northridge 1994 and El Centro 1940 earthquakes. It was found from the analysis that the primary reason for effectiveness offered by rubber bearings in reducing earthquake-induced forces in a building is the lengthening of the first natural vibration period. Moreover, the reduction in forces also depends on the type of earthquake motion. However, the maximum accelerations and base shear force were significantly reduced with the insertion of a rubber isolation system, regardless of the ground motion input.
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