Study On Seismic Behavior Of Single-tower Frame Structure With Large Chassis Using Rubber Isolation Bearing

According to the function of use,the development of the subway superstructure often adopts the structure of a single tower with a large chassis.The sudden change in the stiffness of the structure up and down is extremely disadvantageous to the anti-seismic design.The application of inter-story isolation technology can not only solve the problem of sudden change of stiffness of large chassis,but also reduce the seismic response of the main structure and improve the safety of the structure.Based on a project in Xi’an,this paper carried out an elastoplastic time-history analysis of the subway upper cover structure,evaluated the seismic performance of the inter-story isolation structure,combined with seismic vulnerability analysis,and predicted the probability of exceeding the limit state of the structure.The work done is as follows:(1)The Open Sees finite element program was used to establish a three-dimensional finite element model and compare the dynamic characteristics of the structure before and after the application of seismic isolation technology.The results show that the application of layered isolation technology can effectively reduce the structural stiffness and extend the natural vibration period of the structure.The first three order periods are extended by 105%,131%,and 134%.Far from the excellent period of ground motion,reduce the acceleration response.(2)The time-history analysis of the single-chassis structure with large chassis using isolation conversion and rigid conversion is carried out,and the dynamic response of the structure under rare earthquakes is compared.The results show that the interlayer displacement,acceleration and base shear of the main structure are reduced by more than 30% on average,and the shock absorption effect is significant;base chassis shear and interlayer displacement damping effect of large chassis structure is not obvious,acceleration response even magnifies.(3)Based on the incremental dynamic analysis method,the seismic vulnerability analysis of the anti-seismic structure and the corresponding inter-story isolation structure is carried out.The seismic performance of the inter-story isolation structure is further evaluated and the destruction law of the inter-story isolation structure system is discussed.The results show that compared with anti-seismic structures,inter-story isolation structures have lower damage under the same earthquake.Under the action of rare earthquakes,the overall failure probability of the layered-seismic structure is much smaller than that of the anti-seismic structure.The system’s failure mode is mainly that the horizontal displacement of the isolation bearing exceeds the limit.(4)By adding viscous dampers to optimize the design of layered-seismic structures,the effect of the equivalent damping ratio of the isolation layer on the failure probability of layeredseismic systems under the action of rare earthquakes is studied.The results show that with the increase of the equivalent damping ratio,the failure probability of the layer-seismic structural system shows a trend of falling first and then rising.The failure mode of the structure gradually transitions from the isolation layer to the main structure;the equivalent damping ratio of the isolation layer When the range is 0.28～0.35,it can not only meet the safety requirement of "non-falling earthquake",but also avoid weakening the shock absorption effect of the main structure.