Research On Nonlinear Seismic Response Of Structures Considering The Effect Of Foundation Uplift

Under the action of actual strong earthquakes,some separation of the foundation and foundation soil and structural rocking often occur.Soil and foundations inevitably undergo plastic and nonlinear behavior during strong earthquakes.Since it is unavoidable,can it be used? Out of consideration this problem,allowing the structural foundation to be separated from the foundation soil,the so-called structural rocking analysis has gradually attracted people’s attention.With the deepening of the research,the soil-structure interaction effect has been widely recognized,but the acceptance of the concept of allowing the separation of the structural foundation from the foundation soil is far from enough.In order to further determine the influence of the foundation uplift effect on the seismic response of the structure,this paper uses a combination of theoretical analysis,numerical calculation and model tests to study the influence of the foundation uplift on the seismic response of rigid rocking bodies and flexible rocking structures,respectively.This article first takes rigid blocks on a rigid foundation as the research object,and uses the classic rocking theory analysis model to discuss the rocking seismic response of non-anchored equipment on rigid floor.Then,it proposes a rocking model for flexible structure closer to the actual engineering structure.The multi-layer frame structure shaking table test was conducted to explore the effects of foundation uplift,foundation size and seismic wave type on the dynamic response of the structure.Finally,based on the experimental research,a calculation model considering the foundation uplift effect was established to simulate the test.Compare the results of experiments and numerical simulations to verify the feasibility of the calculation method.Based on this,a large number of parameter analyses are performed to explore the law of seismic response of rocking structures.Based on the research in this article,the following main conclusions can be drawn:(1)The radius of rotation and the critical rotation angle determine the shape,size and rocking characteristics of the rigid block.The rocking response of the rigid block decreases with the increase of the critical rotation angle and the rotation radius;when the excitation frequency is less than 1 Hz,the rigid block is prone to overturn;the rocking response of the rigid block is significantly affected by the type of seismic wave.The rocking spectrum of the rigid block under different inputs is quite different.The rotation response spectrum is very sensitive to the aspect ratio of the rigid block.(2)Shaking table model test results show that the structure will uplift and rocking under the action of a large earthquake;the uplift and rocking of the foundation will cause the horizontal acceleration and vertical acceleration of the structure to increase significantly,while generating more high-frequency components,and the vertical acceleration at the top is reduced;the rocking structure can reduce the seismic effect on the structure to a certain extent.(3)The results of experimental simulations show that the established numerical model can reflect the rocking response of the structure.The parameter analysis based on the model shows that the shear force and bending moment of the bottom of the upliftable model are significantly reduced compared to the fixed case.It can be seen that the internal force distribution of the structure is changed when the structure is uplift and rocking,and its own bending deformation is reduced.The foundation uplift will significantly increase the horizontal acceleration and horizontal displacement response of the structure,and the interlayer displacement of the bottom layer of the structure is often large,which is a weak part of earthquake resistance;the uplift degree of the frame foundation is significantly affected by the size of the foundation,and the interlayer displacement of the structure decreases with the increase of the foundation size.