Design and development of low-cost HDRBs seismic isolation of structures

Abstract

This paper presents a simplified procedure for the preliminary seismic design of high damping rubber bearings (HDRBs) for seismic isolation of structures. The procedure is consistent with the ASCE 7-16 specified seismic design for isolated structure, and starts defining the seismic base shear coefficient (CS) demand for superstructure, reduced by an appropriate response modification factor (RI) for isolated structure. The target time period for isolated structure is identified from the (CS/RI) versus time period plot, corresponding the available base shear capacity of structure. The required lateral shear stiffness of HDRBs is calculated, assuming a reasonable height-to-length ratio of bearing. The preliminary design suggests the required dimensions (height, width and length) of bearing, required thickness of elastomers and number of steel shim plates. The proposed procedure was validated for the seismic isolation of three-story deficient RC frame structure, located in a high seismic zone with a design basis PGA of 0.44 g. Representative reduced scale bearings were locally produced and tested on shake table, using an acceleration time history record of 1994 Northridge earthquake, through multi-levels excitations ranging from 0.10 to 1.0 g. The hysteretic and shear force–deformation response curves were analysed to develop constitutive relationship and hysteretic model for HDRBs. The derived hysteretic model parameters were incorporated in SeismoStruct, using plastic and bi-linear hysteretic models, for testing and validation against the shake table tests. The numerically predicted to experimentally observed peak displacements/forces exhibited a little over-prediction using bi-linear hysteretic model while a little under-prediction using plastic hysteretic model. Combining results from both the hysteretic models, and averaging, minimized the average error to less than 0.10%. Comparative seismic analysis of both as-built and isolated frames was carried out for both design basis earthquakes DBE and maximum considered earthquake MCE (considered as 3/2 of DBE), showing promising behaviour of the simplified design procedure and locally produced HDRBs.