Analysis On Base Isolation Mechanism Of High-rise Shear Wall Structure With Large Height-width Ratio And Shake Table Investigation

Concrete pure shear-wall structure is widely used in high-rise residential buildings in China,which has advantages of strong integrity and great lateral stiffness.At the same time,under the action of strong earthquake,the shear-wall structure may suffer from severe shear failure of connecting beams,wall collapse and damage,etc.,which are difficult and costly to repair.Being supported by the national science and technology support program“Key Seismic Technical Research and Demonstration on Housing Reconstruction”,analysis and experimental study on overturning resistant mechanism,effective and simple isolation analyzing method,damping effect evaluation index analysis and control have been conducted.Firstly,the peak response of the translational and overturning angular displacements of the isolated layer of high-rise shear wall structure,under the earthquake excitation,are analyzed,based on the complex modal frequency response analysis method.The influence of the height-width ratio,the equivalent damping ratio of horizontal and overturning direction,and the overturning kinetic energy of the superstructure are discussed.The dynamic overturning analysis method,considering the overturning kinetic energy of the superstructure,is established,and the calculation formula of the limit ratio of height-width,based on the given condition that the isolation bearing is not extended,and the influence law of the overturning kinetic energy is revealed.Secondly,the simplified analysis method of isolation layer parameters is proposed based on the expected seismic reduction targets,considering the elastic deformation and overturning kinetic energy.The validity and accuracy of the method are verified by comparing the results of finite element time history analysis and simplified calculation.Furthermore,the equivalent beam continuity model of high-rise shear wall structure is established,and the relationship between the equivalent stiffness ratio and the structural period ratio,the effective vibration mode participating mass and the damping ratio of vibration mode is analyzed.The control rules of critical stiffness ratio and cri tical period ratio to base shear force ratio and moment ratio?horizontal seismic reduction coefficient?are revealed.Finally,a1:12.5 scaled model was designed and made for a high-rise shear wall base isolated structure with a height-width ratio of 3.96 in a high seismic intensity area,and shaking table tests were carried out.The results show that:1.The maximum overturning angle of the isolation layer will synchronously occur with the maximum horizontal displacement.Increasing the horizontal equivalent damping ratio of the isolation layer has a significant effect on reducing the peak horizontal displacement and peak turning Angle of the isolation layer,but changing the vertical damping ratio of the support,namely the flip damping ratio,has little influence on the translational and overturning angular displacement of the isolation layer.2.Ignoring the overturning kinetic energy of the superstructure will overestimate the height-width ratio limit.The deviation of the results from dynamic and static method decreases with the increase of seismic intensity,seismic isolation structure period and site dominant period,and increases with the increase of the horizontal equivalent damping ratio of the isolation layer.With other design conditions unchanged,reducing the mass of the superstructure and increasing the total vertical stiffness of the isolation bearing are beneficial to improve the height-width ratio limit of the shear wall structure.3.The simplified analysis method of control parameters base d on the expected seismic reduction targets can be used to conveniently and accurately calculate the isolation layer parameters that meet the requirements of the damping target,and provide guidance for the adjustment of the overall equivalent stiffness of the superstructure.The seismic response analysis method of equivalent beam model considering the boundary of isolation layer has good calculation accuracy.This method can be used for the qualitative research and optimization analysis of the macro-index related to structure.4.When the basic period ratio r_{T 1}>1.3 or equivalent stiffness ratio r_kh>0.8,the high-order vibration mode response of the isolation structure can be effectively suppressed,and the influence of the basic mode on the seismic response of the structure can only be considered.When r_kh>1(r_T1>1.43),the damping ratio of isolation layer can be approximately taken as the damping ratio of the fi rst vibration mode of isolation structure.5.When the basic period of base isolated structure T_{I 1}<5_gT,the evaluation index of the seismic reduction effect should be the base shear force ratio of the isolated to base fixed structure.WhenT_{I 1}>5_gT,there will be critical stiffness ratio r_khB and critical period ratio r_T1B.And the two critical ratios are independent from the damping ratio and mass of the structure.When r_kh<r_{kh B}or r_T1<r_T1B,the base moment reduction effect is worse than the shear force,so the bottom moment ratio should be the control index;otherwise,the base shear force ratio should be the control index.6.The results of the shaking table test show that the base isolated shear wall structure with large high-width ratio is also of good seismic performance.The acceleration attenuation of the superstructure is significant,and the superstructure can remain basically elastic under the fortification intensity earthquake,and there is no overturning or serious damage under very rare earthquake.It is effective and feasible to apply the basic seismic isolation technology to the high-rise and super-high-rise shear wall structures with large height-width ratio in the high-intensity area.The above analysis method and the conclusion of the research can provide valuabl e reference and basis for the research and practical engineering application of base isolated high-rise shear wall structure with large height-width ratio.