Experimental investigation and analytical solution for the coupled seismic response of 3D base-isolated structures

This study systematically investigates the coupled horizontal-rocking seismic behavior of three-dimensional base-isolated structures (3D-BISs). First, a simplified analytical model accounting for superstructure flexibility is developed for the 3D-BIS. This model is used to conduct modal analysis, which reveals the influence of various design parameters on the coupling mechanism between horizontal and rocking motions. Subsequently, a novel multi-dimensional earthquake isolation and mitigation device (denoted MEIMD) is proposed to enhance seismic isolation efficiency and mitigate rocking effect of the 3D-BIS. Numerical simulations are conducted to explore the nonlinear rocking stiffness of the MEIMD. To evaluate the dynamic response characteristics of the 3D-BIS under rocking effect, full-scale horizontal shaking table tests are performed on a steel frame model (aspect ratio >3). The results indicate that the coupled motion mode leads to a gradual increase of horizontal peak floor acceleration from the second floor toward both the top and bottom of the 3D-BIS. The rocking effect induces a rigid-body rotation of the superstructure, which amplifies the horizontal displacement of the 3D-BIS while not increasing structural internal forces. Neglecting the superstructure flexibility may underestimate the rocking effect and the response contribution from high-order vibration modes, particularly for 3D-BISs with large aspect ratios. Finally, comprehensive comparisons between the analytical solutions and test results validate that the proposed model can reliably predict the coupled seismic response of the 3D-BIS.