Study Of Three-dimensional Bearing With Variable Stiffness And Its Seismic Isolation Performance For Long-span Spatial Structures

Due to the large span of long-span spatial structure,its vertical vibration is significant under the action of earthquake,and the vertical response and horizontal response can reach the same level,resulting in complex spatial responses of long-span spatial structure.In addition,strong seismic observations show that the amplitude of vertical component of some earthquakes is larger than that of horizontal component.Therefore,from the point of view of economy,functionality and safety,it is of great significance to study the three-dimensional(3D)seismic isolation for long-span spatial structures.A 3D isolation with variable stiffness is developed in this paper.Tests have been carried out to study the dynamic charicteristics and isolation performance of the 3D isolation.In addition,simulations have been conducted b for single-layer spherical reticulated shells.The main contents and conclusions of this paper are as follows:(1)On the basis of the developed vertical bearing with variable stiffness for longspan spatial structure,a 3D isolation is developed by connecting the vertical bearing and the horizontal friction pendulum bearing with decoupled movement charicteristics,and the overall design of the 3D isolation system which connects multiple isolations is proposed.Static loading test of the 3D isolation is carried out,and the difference of the stiffness,force and displacement of the threshold for the variable stiffness characteristics between the test results and the calculated results is no more than 6%.Because of the damping in the system,the vertical hysteresis curve of the isolation has notable differences with the design one under high velocity sinusoidal excitation.In the shaking table test,the bearing has a satisfactory isolation effect on the acceleration input.The average isolation ratio is 48% for vertical acceleration,89% for horizontal acceleration.(2)The seismic isolation performance of 3D isolated single-layer spherical reticulated shells considering traveling wave effect is studied using the numerical model without seismic isolation,with horizontal seismic isolation,and with 3D isolation.The results show that the 3D isolation can effectively reduce the interal movement of the elements and thus has a higher control effect over the horizontal seismic isolation.The control effect of the 3D isolation bearing on the peak acceleration of structure and the axial force of the bar under the traveling wave effect is 86% and 56%.(3)The seismic isolation performance of 3D isolated single-layer spherical reticulated shells with soft soil foundation is studied.The dynamic response of singlelayer spherical reticulated shells without seismic isolation,and with 3D isolation having non-variable stiffness and variable stiffness characteristics is calculated for the cases with or without considering soil-structure interaction.By analyzing the acceleration at the top of the structure and the axial force of the bar,the efficiency of 3D seismic isolation is reduced when the soil-structure interaction is considered,acceleration isolation efficiency decreased by about 4%～15% and axial force isolation efficiency decreased by about 0～10%.