Feasibility evaluation of pre-pressed spring devices for vertical isolation of single-layer spherical lattice shell structures

Abstract

Single-layer spherical lattice shells are typical spatial structures for large-scale landmarks and public buildings. If such buildings are located in strong-earthquake zones, their seismic resilience must be considered. Long-span spatial structures are highly sensitive to multi-component ground motions, and vertical ground shakings lead to strong structural vibrations. Although a few vertical isolators with invariant stiffness have been developed, they are generally too stiff to effectively isolate vertical seismic shakings. In this paper, a nonlinear vertical isolator using pre-pressed and restrained helical springs called pre-pressed spring device (PSD) is proposed. The main advantages of the PSD are that it not only provides a high first stiffness and large bearing force to support the weight of the isolated object but also possesses sufficiently low stiffness to isolate vertical ground motions. In a vertical isolation system, PSDs are employed as basic load-carrying elements, and viscous dampers can be introduced into the system to function as additional energy dissipation devices. The configuration, working principle, and mechanical model of the newly developed PSD are described and explained in detail. Cyclic loading experiments were performed on a prototype PSD to investigate its actual force–displacement relationship. The experimental results showed that the PSD specimen exhibited multilinear elastic behaviors with clear first and isolation stiffness properties. A novel numerical model of the PSD was constructed, and the accuracy of the model was validated by comparing the simulation and experimental results. Subsequently, PSD-damper assemblies and friction pendulum bearings (FPBs) were used to form three-dimensional (3D) isolation bearings for a single-layer spherical lattice shell with surrounding columns. The seismic responses of the controlled structure were evaluated using nonlinear time-history analysis. The numerical results revealed that the PSDs achieved effective static-load support and vertical isolation, and that the entire 3D isolation bearings significantly improved the seismic behavior of the lattice shell structures in all three directions.