Investigation of damping type and damping ratio for nonlinear seismic analysis of base-isolated steel structures

Seismic isolation systems are essential components in improving the earthquake resistance of structures by reducing the forces transmitted to the building during seismic events. These systems come in various types, such as elastomeric bearings and sliding bearings, each offering unique advantages in terms of energy dissipation and flexibility. While seismic isolators have been widely studied, the determination of damping type and damping ratio in numerical analysis of base-isolated steel structures is a significant phenomenon. In this study, two separate experimental investigation involving steel structures with seismic isolators were selected for numerical analysis. The lead rubber bearing isolators were used in both 1/20 scaled 2-story steel structure and 1/16 scaled 4-story steel structures in the experimental tests and numerical modelling. The nonlinear time history analyses were performed to evaluate how different damping types influence the seismic response of the isolated structures. In the numerical models, mass-proportional, stiffness-proportional, and Rayleigh damping types and different damping ratios ranging from 1% to 8% were used. The numerical analysis results were compared with the experimental results by considering displacement values at different floor levels. The closest approximations to experimental results were achieved with a 6% damping ratio for mass proportional damping type, and a 1% damping ratio for stiffness-proportional and Rayleigh damping types. The findings provide insights into the optimal selection of damping ratios for accurately simulating the behavior of steel structures equipped with Lead rubber-bearing seismic isolators.