Seismic response of isolated structures with an improved model of the UFREI

Abstract

An improved formulation of the horizontal shear behavior of the unbonded fiber-reinforced elastomeric isolators (UFREI), which predicts both the pre-rollover and the post-rollover behavior considering the effect of the vertical load, is proposed. A simplified and computationally inexpensive formulation of the horizontal shear behavior of the UFREI has also been proposed afterward. Further, these formulations are verified using experimental results and compared with the results obtained using the other earlier methods in the recent literature. The horizontal shear behavior predicted by both of the proposed formulations is observed to fit the experimental results very well. The shear behavior predicted by these formulations is observed to be more accurate than the corresponding predicted by the other formulations from the recent literature. A parametric study characterizing the effect of the vertical pressure and the initial elastomeric shear modulus on the horizontal shear behavior of isolators is also carried out. The proposed formulations are further used to model the behavior of the UFREI employed to isolate the benchmark structure considered in the study.Supplementary damping devices are further installed alongside the nonlinear UFREI isolation system to mitigate the excessive displacement demand on isolators under near-fault ground motions. The isolated benchmark structure is thus coupled with a Magneto-rheological Damper (MRD) with an improved control algorithm for nonlinear isolation systems in three configurations, i.e., semi-active, passive-on, and passive-off. A comparative study of these configurations shows that MRD in passive-on mode provides the minimum isolators displacement response, but an overall improved structural response is achieved with MRD in the semi-active mode of operation.