Unbonded Fiber-Reinforced Elastomeric Isolators for Isolating Masonry Buildings

This study focuses on the design procedure and development of the unbonded fiber-reinforced elastomeric isolator (UFREI) and its application to prevalent masonry building practices in developing countries. The proposed design procedure caters to the development of rectangular UFREIs with or without modifications, considering an improved shear behavior formulation. Afterward, the proposed design procedure is used to design the isolation system for a pre-existing base-isolated masonry building located in the Tawang district in the northeastern state of Arunachal Pradesh in India. Three different configurations of the above building [i.e., fixed base, isolated using square UFREIs, and isolated using modified rectangular UFREIs (MR-UFREI)] are considered for a comparative response analysis under a set of probable ground motions during a service period of 100 years. The building is modeled in SAP2000, where it is subjected to nonlinear time-history analysis under the considered set of ground motions. The masonry walls are modeled as nonlinear layered shell elements, and concrete floors as rigid diaphragms. An improved shear formulation of UFREI is used to model the isolation system as a combination of a multilinear elastic spring and a dashpot. Major response parameters, i.e., floor accelerations, isolator displacement, interstory drift ratio, etc., are investigated, and a significant improvement is witnessed throughout with the use of the MR-UFREI isolation system. The stress–strain distribution and concentrations in the masonry structure and isolation system are also investigated. These distributions are further used to quantify the fatigue losses to the elastomer layers used in the isolation system during the design period, which is found to be minimal.