Equivalent Linearization Analysis Method for Base-isolated Buildings

Base isolation system, as one of the most popular means to mitigate the seismic risks, often exhibits strong nonlinearity. To simplify the procedure of structural design, bilinear force-deformation behavior is recommended for isolation systems in most modern structural codes. Although base isolation system can be analyzed through nonlinear time history method, solving of a system with a large number of degrees of freedom may require an exorbitant amount of time. As a substitute, the equivalent linearization method is frequently used. Apparently, under given earthquake ground motions, the accuracy of equivalent linearization analysis method is significantly related to the estimation of equivalent linear properties. How to improve the estimation accuracy of this approximate method constitutes a subject of wide and deep interest among researchers around the world. In this research, the equivalent linearization analysis method for base-isolated buildings was investigated. The literature survey on related aspects of base-isolated buildings was carried out firstly. Then, the estimation accuracy of fifteen equivalent linearization methods selected from the literatures was evaluated when subjected to twelve earthquake ground motions. After that, from simplicity to complexity, the base-isolated buildings were modeled using single-degree-of-freedom (SDOF) systems and multi-degree-of-freedom (MDOF) systems, respectively. For both considered systems, more comprehensive parametric analyses were performed with varying the parameters selected from the isolation system and the superstructure. Accordingly, improved equivalent linearization methods were derived for SDOF and MDOF systems to improve the prediction accuracy of the maximum displacement of isolation systems. Based on the proposed equivalent linearization methods, different analysis methods for base-isolated buildings were assessed, including equivalent static linear analysis, response spectral analysis, linear and nonlinear time history analyses. It was found that with the proposed equivalent linearization methods equivalent linear analyses could yield more accurate results when compared with the equivalent linearization method recommended by structural codes. As a result, the proposed equivalent linearization method could be potentially useful for the design and analysis of baseisolated buildings, as least in the preliminary stage of structural design.