Dynamic Response Analysis Of Isolation Structure With Limit Device Under Bidirectional Ground Motion

Under the action of near-fault ground motion,the deformation of the isolation layer of the isolation structure may exceed the design value.The deformation can be effectively reduced by adding a limiting device to protect the isolation facilities.However,the limiting effect and adverse influence of the limiting device under the action of bidirectional ground motion are still unclear.In this paper,unidirectional eccentric and bidirectional eccentric foundation isolation structural steel frame models were established by OpenSees software,and bidirectional ground motion was input to study the dynamic response of the structure,analyze the limit effect of the limit device,and the influence of the limit on the dynamic response of the isolation structure.The main research contents and conclusions are as follows:(1)OpenSees software was used to establish the isolation structure with limit devices,and Zero Length Impact3 D element was used to simulate the collision between isolation layer and limit device.A shaking table test model was made,three kinds of springs with different stiffness were selected as the limit device of the isolation layer,and three near-fault ground motions were selected to input the structure.The results show that the numerical simulation results are in good agreement with the experimental results,which indicates that the isolation structure with the limit device established by OpenSees software can simulate the dynamic response of the structure and the limit device collision.(2)Based on OpenSees software,non-eccentric isolation structures,three unidirectional eccentric isolation structures and three bidirectional eccentric isolation structures were established respectively.Ten groups of near-fault seismic waves were selected to study the effect of eccentricity on dynamic response of isolated structures under bidirectional ground motion.The results show that with the increase of eccentricity,the interlayer displacement angle of all isolated structures increases in one direction and decreases in the other.Floor acceleration,displacement of isolation layer,torsional displacement ratio,torsional angle and torsional acceleration increase with the increase of eccentricity.Displacement of isolation layer exceeds the standard value when eccentricity is large,and corresponding limiting measures should be taken for isolation layer.(3)Elastic limiting devices were set around the isolation layer,three kinds of limiting stiffness and three kinds of reserved gap were designed,a total of nine limiting conditions,ten groups of bidirectional ground motion near the fault are input,and the dynamic response of the non-eccentric,unidirectional and bidirectional eccentric isolation structures with limiting devices was studied.The results show that the interstory displacement angle,floor acceleration,torsional displacement ratio,interstory torsion angle and torsional acceleration increase under the limit condition,which is proportional to the stiffness of the limit and inversely proportional to the reserved clearance.The displacement of the isolation layer decreases more with the increase of the limiter stiffness and less with the increase of the reserved clearance.The reduction is the least at 1 time stiffness.However,the displacement of the isolation layer can still be limited within the standard value.Under the same limiting conditions,the growth rates of the interstory displacement angle,floor acceleration,interstory torsion angle and torsional acceleration of the isolation structure with different eccentricities are close,and the displacement reduction ratio of the isolation layer is close.