Study On Unfavorable Seismic Behavior Of The Isolated Structure Under Long-period Earthquake And Controlling Research

Seismic isolation technology is an increasingly mature vibration control technology for structures,which is more and more widely used in practice.Its seismic isolation effect has been tested through actual earthquakes for many times and its seismic performance has been proved to be significantly better than traditional non-isolated structures.However,under the action of some long-period earthquakes,such as near-field pulsed ground motions and far-field long-period ground motions,the isolated structures may be adversely affected.At present,many studies have confirmed that near-field pulsed ground motions can damage the isolated structures.But there are few studies on the adverse effects of far-field long-period ground motions on the isolated structures.So that it is particularly important to carry out the relevant research,in the case that the earthquake damage records have confirmed its destructive effect of the far-field long-period ground motions.According to the relevant literature and studies on the characteristics of different types of ground motions,in this paper,the criteria of selecting ground motion are drawn up,and several conventional ground motions and several far-field long-period ground motions are selected.Based on an engineering example,a nonlinear analysis model of base-isolated frame structure is established by using the Seismostruct software.The dynamic time-history analysis method is used to study the seismic response of structures under large earthquakes,furthermore the seismic performance of the structures is studied from the point of view of statistics and probability by using the incremental dynamic analysis method to analyze the seismic vulnerability of the structures.Based on the unanticipated seismic behavior of the structure,three different kinds of viscous damper arrangement schemes are established,and according to the above analysis method,the effects of different control measures are studied.The conclusions of the study are as follows:1)by comparing the ground motion duration of conventional ground motion with that of near and far-field long-period ground motion,the results show that the ground motion duration can distinguish between conventional ground motion and long-period ground motion,but the distinction between near-field and far-field long-period ground motion is not obvious.2)By studing the correlation between the seismic intensity measures of long-period ground motions and seismic response of teh isolation structure,the results show the correlations of acceleration-related and velocity-related seismic intensity measure are obvious,but the correlations of displacement-related seismic intensity measures is poor.Therefore,it is suggested that in the seismic analysis of engineering,if the period before isolation T₁?2.0s,the index I_c is better,and if T₁>2.0s,the index PGV should be selected.3)Study on seismic response characteristics of structures under large earthquakes and seismic vulnerability analysis based on incremental dynamic analysis found that the damage probability of base-isolated frame structures increases obviously under the action of long-period far field ground motions,and the seismic performance decreases.According to the characteristics of deformation distribution,the deformation is mainly concentrated on the bottom of the structure and which is the"weak layer"of the structure.4)Based on the characteristics of the seismic response distribution of the isolated structures,the control effect of viscous dampers with different arrangement schemes for seismic response of the isolated structures is studied.The result shows that viscous dampers can improve the seismic performance of the base-frame isolated structures,but the seismic responses of other floors will be increased by adding viscous dampers in different floors.In order to achieve a balanced control of the seismic response of all floors and better improvement of the seismic performance of the base-frame isolated structures it is suggested that viscous dampers should be added in the weak areas to improve the seismic performance of the structures.