Real-Complex Hybrid Modal Response Spectrum Method for Seismically Base-Isolated Structures

This paper proposes a real-complex hybrid modal response spectrum method (RCHM-RSM) for the design of seismically base-isolated structures. In contrast to the complex modal response spectrum method (CM-RSM), the proposed method not only improves the accuracy of the structural response but also avoids complex calculations. It has been observed that the use of conventional methods to construct damping matrices of base-isolated structures may cause a significant reduction in calculation accuracy. Thus, a new approach is proposed for determining damping matrices of base-isolated structures by assembling the damping matrices for substructures. In addition, an iterative analytical procedure is introduced that integrates equivalent linearization with real and complex mode theories. A benchmark base-isolated structure is presented as a numerical example to evaluate the efficacy of the proposed method. The numerical results of the novel method were compared to those obtained from the CM-RSM, forced decoupling response spectrum method (FD-RSM), and nonlinear time history analysis (NTHA). The research results show that the use of the proposed RCHM-RSM can effectively improve the analysis accuracy of the base-isolated structure, which possesses the advantage of high performance, high efficiency, flexible and ease of use. The results also show that the currently used damping models of base-isolated structures may overestimate the damping effect of the structure and thus underestimate the structural response.