Effect of frequency dependence on the seismic performance of linear viscoelastic base-isolated structures

The purpose is to address two issues arising from the frequency dependence of viscoelastic (VE) isolation bearings implemented in base-isolated structures (BIS): (i) how the frequency dependence affects the structural response; and (ii) which method is appropriate for the VE BIS. Effects of the frequency dependence on the absolute acceleration transmissibility are analyzed based on a two-degree-of-freedom system. Three generic algorithms: (i) constant-parameter approximation (CPA), (ii) mode superposition iteration, and (iii) modified rational polynomial approximate (RPA) are used to calculate the seismic responses. Effects of the frequency dependence on the seismic responses of the VE BIS subjected to the historic earthquakes are numerically analyzed through a five-story frame structure. The results show that the frequency dependence of the stiffness can broaden the absolute acceleration transmissibility curve of the VE BIS. The seismic responses in general are underestimated when the frequency dependence is not well considered, and the response errors are influenced by the frequency dependence, excitation characteristics and structural dynamic property. The RPA method takes into account the frequency dependence of VE isolation bearings completely through the rational polynomial model. The CPA and mode superposition iteration methods can only consider frequency dependence effect partially, and the mode superposition iteration method performs better.