Theoretical And Experimental Study On Dynamic Response For Curved Surface Isolated Strucrture

The development of economic and urbanization have created great wealth,however,the tremendous casualties and societal devastation induced by earthquake disasters becoming more and more seriously.As an effective method to reduce the seismic response,base isolation technology has been studied deeply and used in the practical engineering widely.Base isolation technology,by placing a flexible isolation layer between the bottom of the structure and the foundation,can effectively reduce the seismic response by reducing the energy input to the upper structure.The isolation layer of conventional isolation system may produce excessive displacement under super-design earthquake,which could result in bearing damage and collision of isolated structure and retaining walls.Structural collisions can not only caused damage to the structure,but also induced an overturning moment to the structure.For this reason,the curved surface isolated structure system,which can reduce the displacement of the isolation layer using the characteristics of curved surface movement and the gravitational effect of superstructure,was proposed in this paper.The theoretical and experimental research has been carried out for this innovational isolation system.The main contents and achievements are as follows:(1)The simplified single-particle model of curved surface isolated structure,using the method of stiffness decomposition,was established and analyzed theoretically.Firstly,the relationship between isolation period and ratio of radius to heights was analyzed theoretically.Subsequently,the acceleration and displacement transfer coefficient for the curved surface isolation structure were derived by using the dynamic equations.The relationship between transfer coefficient and ratio of radius to heights for curved surface isolated structure was studied and compared with that of conventional isolated structure.Finally,the overturning resistant ratio for curved surface isolated structure and conventional isolated structure were studied comparatively.(2)A two-degree-of-freedom model was established considering the rotational movement around the curvature center of the curved surface isolated structure and the rocking movement of the upper structure around the center point of the curved isolation layer.The two DOF model also considered the influence to the horizontal stiffness of the bearing caused by torsional motion.The change rules of acceleration response of the structure,displacement response of isolation layer and hysteretic characteristics of bearing with the ratio of dimeter to heights are studied by using MATLAB theoretically.(3)A curved surface isolated structure model using friction sliding bearings was designed and fabricated,and a shaking table test was carried out to study its dynamic response characteristics.The curved surface isolated structure models were adopted friction sliding bearings with different curvature radii of 2.5m,4m and 7m.The uni-directional loading shaking table tests for the curved surface isolated structure models were carried out to study the effects of the radii of curved surface isolation layer on the structural acceleration response and displacement response.For comparison purpose,a conventional isolated structure model with plane friction sliding bearings was also tested.The displacement of isolation layer for the conventional isolated structure model was increased fast.The residual deformation of isolation layer was large and the model had no self-resetting ability.With the increase of peak loading acceleration,the structural overturning effect is more and more obviously.The rate of increase of displacement and residual deformation of isolation layer for the curved surface friction sliding isolated structure model were significantly reduced relative to that of conventional isolated structure model during the shaking table test.The curved surface isolated structure model showed the self-resetting ability and it had a significant influence on the structural acceleration response.(4)In order to study the dynamic response characteristics of the curved surface isolated structure with laminated rubber bearings,two models with inclined isolation bearings,inclination angles were 4 degrees and 8 degrees,were established and tested via shaking table.For the purpose of studying the effects of loading systems and ratio of radius to heights on the acceleration response,displacement response,hysteretic characteristics of bearing and displacement of isolation layer,the test models were subjected to horizontal uni-directional loading,horizontal + vertical bi-directional loading,horizontal bi-directional loading and horizontal + vertical three-directional loading shaking table test.A similar conventional isolated structure model and a non-isolated structure model were also tested for comparison purpose via shaking table.The experimental results show that the acceleration response of the curved surface isolated structure is larger than that of the conventional isolated structure model and it is increased with the inclination angle of the bearings.However,the acceleration response of curved surface isolated structure model is significantly reduced relative to that of non-isolated structure model.The displacement of isolation layer for the curved surface isolated structure is reduced relative to that of conventional isolated structure model,and the decay rate of the isolation layer is higher than that of the conventional isolated structure model.The curved surface isolated structure can recover to a stable state more quickly under earthquake.(5)In order to verify the test results,the finite element model of conventional isolated structure model and curved surface isolated structure models with 4 degrees and 8 degrees inclined isolators were established by ABAQUS respectively.The shaking table test conditions were simulated and compare the numerical simulation results with the results of the shaking table test.The analysis results show that the phase characteristics of structural acceleration response and displacement response time history curves obtained by numerical analysis are consistent with that of shaking table test results.The hysteretic curves of isolator obtained from numerical simulation shows that the equivalent stiffness is consistent with the experimental results.The damping effect of the curved surface isolated structure was confirmed.