Bi-Directional Response of Base Isolated Structures Subjected to Near-Fault Ground Motions

Abstract eng:
This paper presents the results of a parametric study on the effect of near-fault ground motions on the response of base isolated structures. The isolator-structure system is modeled as a rigid mass mounted on a single isolation bearing. An analytical model based on classical rate-independent plasticity is used for representing the bidirectional coupling effect and the bilinear behavior exhibited by many of the current seismic isolation devices. A series of time history analyses is carried out using two pairs of input ground motions (N-S and W-E horizontal components) recorded during the major event of the 1999 Chi-Chi Taiwan earthquake. Both ground motions have been recorded in locations close to the generating fault but only one presents strong near-fault characteristics. In each of the analysis sets the model parameters are varied and the system responses compared. The results of this study confirm that near-fault ground motions are associated with larger isolator deformation demands. Furthermore, the results indicate that, among the three parameters that characterize the bilinear oscillator model, the isolator strength, or equivalently the yielding force, is the key parameter to reduce isolator deformations when subjected to near-fault ground motions.

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