Numerical Studies of Three-Dimensional Isolated Structures with Vertical Quasi-Zero Stiffness Property

Abstract

ABSTRACT A novel three-dimensional (3D) seismic isolator combining the quasi-zero stiffness (QZS) system in the vertical direction with the friction pendulum system in the horizontal direction is presented and applied to a moderately tall building model. The isolation system dynamic properties are first assessed in vertical and rotational directions separately using a simplified 3D model based on an equivalent analytical method with the frequency-amplitude functions and displacement transmissibility curves. The effectiveness of the 3D isolation system is then verified through numerical time history analysis of a tower building with a bottom podium modeled in OpenSees including a new numerical element representative of the 3D isolators implemented in the software. A comparison of the dynamic response is made between a fixed-base model, a 2D isolated model with friction pendulum bearings in the horizontal direction only, and the novel 3D isolated model. The input excitations consist of strong earthquake shaking and low-amplitude field recorded metro vibration. Results demonstrate that the 3D isolator can effectively reduce the seismic actions in three directions compared with the fixed based model and the 2D isolated model. The overturning movement can be controlled within safe limits under maximum considered earthquakes. In addition, the 3D isolators can significantly decrease human discomfort from high frequency environment vibration.