Floor response spectra–oriented acceleration mitigation of base-isolated structures with rate-independent damping

Abstract

Engineering structures accommodating acceleration-sensitive non-structural equipment exhibit an intrinsic incompatibility in seismic demand control, as base isolation effectively suppresses inter-story drift, whereas the introduction of linear viscous dampers to restrain isolator displacement frequently leads to amplified accelerations of the structural floor and equipment within. This trade-off poses a critical challenge for achieving simultaneous control of deformation- and acceleration-related demands. To resolve this incompatibility, a rate-independent damping-integrated isolation system (RIDIS) is proposed, in which the superior low-frequency energy dissipation capability of rate-independent damping (RID) is exploited as the primary mechanism for mitigating floor and equipment acceleration demands. A mechanical model that incorporates equipment–structure interaction and RIDIS is formulated, from which a Fourier-transform-based time-domain solution is established to approximate the ideal but non-causal RID operator while retaining its frequency-insensitive damping characteristics. Accordingly, the floor response spectra of the original structure, structures isolated by the normal isolation system, and RIDIS are established. Parametric analyses are performed to quantify the dependence of floor and equipment acceleration reductions on site spectral features, isolation period, and loss stiffness ratio of RID. A floor response spectra-based design methodology is further developed by statistically synthesizing design spectra from computed floor response spectra, enabling rapid assessment of structure and equipment acceleration demands, the effectiveness of which is validated by a design case. Simultaneously, the time history analysis results demonstrate that, under the same displacement of the isolation layer, RIDIS achieves substantially enhanced acceleration suppression of both structure and equipment compared to linear viscous damper–integrated isolation due to the synergistic action of isolation and rate-independent damping, while the calibrated design spectra provide practical guidance for preliminary design. The discussion on the causal realization mechanism of the RID identifies its potential for practical engineering applications. Consequently, RIDIS establishes an acceleration-oriented isolation strategy that reduces damping force demand without compromising the overall seismic resilience of the isolated structures.