Feasibility study of a practical causal rate-independent damping device for the improved performance of seismic isolated structures

When rate-independent linear damping (RILD) is incorporated into a base-isolated structure, it achieves a similar response displacement reduction effect with significantly lower floor response acceleration compared with linear viscous damping (LVD) with the same loss factor. To address the undesirable stiffness added to an isolation layer when we adopt a mechanical device comprising a few branches of a spring–dashpot link to realize RILD, this study proposes canceling the undesirable isolator stiffness by adding an inerter element and reducing the isolator stiffness. A heuristic optimization method was developed to design the proposed mechanical device to mimic the behavior of RILD. A parametric survey on the optimal designs of the device suggests that the three branches of the spring–dashpot link work best in terms of practicality and feasibility. Seismic control performance was assessed using a 10-story base-isolated building mounted on linear and nonlinear isolation systems. Analyses of linear systems revealed that the proposed device achieved lower inter-story drifts and approximately 40% reduction in floor response acceleration with a 4% increase in isolator displacement compared with the LVD when subjected to high-frequency ground motions. Analyses of the nonlinear systems showed that the displacement control performance of the proposed model was slightly compromised when subjected to ground motions dominated by low-frequency components, thereby identifying a further challenge in developing a causal RILD device for nonlinear structures.