Limitation of base isolation in protecting freestanding contents in buildings

Abstract

AbstractSeismic base isolation performs well in protecting the drift‐ and acceleration‐sensitive elements in buildings, while its effectiveness in reducing the velocity response and thus protecting velocity‐sensitive elements remains unclear. Through laboratory tests and numerical simulations, this paper shows that base isolation does not adequately control the floor velocity to the same level as the drift and acceleration, particularly on lower floors and under pulse‐like ground motions with rich long‐period contents. This limitation is attributed to the frequency‐insensitive velocity spectra of the ground motions and the significant difference in the mode shapes between base‐isolated and fixed‐base buildings. This limitation is demonstrated by comparing the loss ratios of rocking‐dominated freestanding contents due to overturning in base‐isolated buildings and their fixed‐base counterparts. By assuming a uniform distribution of randomly generated freestanding contents and adopting different overturning fragility models, the results show that the base isolation may be ineffective in reducing the loss ratio of rocking‐dominated contents in a building and may even adversely increase the loss ratio, especially for large objects, and when low‐ and moderate‐seismic intensities are concerned.