Seismic Performance Analysis And Experimental Study Of Self-centering Variable Damping Energy Dissipation Brace

Structures have different demands of vibration mitigation and energy dissipation under different vibration levels.However,the sliding force of existing self-centering energy dissipation braces is usually large,and braces are unable to take both strong and weak vibration cases into account.Self-centering energy dissipation braces do not slide under weak vibration level or have no sufficient energy dissipation capability under strong vibration level,and as a result,cannot fully utilize their own seismic capacity under different vibration levels.Meanwhile,the stiffness change of self-centering energy dissipation braces before and after sliding has great influence on the total stiffness of the whole structure.The nonlinear degree of structural response increases with the increase of the stiffness change,so the difference of the stiffness of braces before and after sliding should not be too large.In this paper,a new type of self-centering variable damping energy dissipation brace is proposed to solve the high sliding force and stiffness mutation problem of existing self-centering energy dissipation braces.Combination disc springs are used to provide self-centering capability,and magnetorheological fluid variable damping energy dissipation is realized by configuration design.The main research contents are as follows:(1)A new type of self-centering variable damping energy dissipation brace is developed.Working mechanism of the variable damping force is explained.By arranging several grooves at the inner side of the outer tube,the gap of piston and cylinder of brace is changed at different working stages,and the damping force can be adjusted.The segmentation model of self-centering variable damping energy dissipation brace is developed.The whole process of brace in tension or compression is divided into 7 stages,rigid loading,variable damping force loading,ultimate damping force loading,rigid unloading,ultimate damping force unloading,variable damping force unloading and self-centering unloading.The brace has symmetry of tension and compression during the cyclic motion,and exhibits a full similar flag shaped hysteretic curve by superposing self-centering and energy dissipation capability.Six design boundary conditions based on performance requirements of brace are proposed to fully utilize the outstanding performance of brace,which are to meet requirements of ultimate bearing force,design stroke,and supporting force of the combination disc springs,to be in elastic stage,to consider different vibration levels and to have small variable damping force region.(2)The magnetic field of brace is simulated.Under the action of permanent magnet,the damping force decreases with the increase of the gap of piston and cylinder.The magnetorheological fluid can meet the application demands at different gaps,and the design principle of variable damping force is feasible.Self-centering variable damping energy dissipation brace is simulated.The brace exhibits a full similar flag shaped hysteretic curve with a low sliding force of 151kN,no residual deformation and symmetry of tension and compression.The energy dissipation capability increases with the increase of excitation amplitude.The brace has stable and reliable bearing force,and can meet the performance demands of different vibration levels.The effects of design parameters on hysteretic behaviors of self-centering variable damping energy dissipation brace are analyzed.To decrease the sliding force,increase sliding stiffness ratio and equivalent viscous-damping ratio,meet the demand of ultimate bearing force,reduce the residual deformation energy dissipation ratio to 0 and improve the self-centering and energy dissipation capability,the pre-pressed force of combination disc springs should be larger than the initial damping force,meanwhile,the stiffness of combination disc springs and the ultimate damping force should be increased,and the variable damping force region should be decreased.Compared with the existing self-centering energy dissipation braces,the sliding force of proposed brace is significantly reduced,the sliding stiffness ratio is increased,and the equivalent viscous-damping ratio and the ultimate bearing force under the same design of pre-pressed force and stiffness of combination disc springs are also increased,which is good for the response control of structure under different vibration levels.(3)A self-centering variable damping energy dissipation brace with the total length of 2.1m is designed and fabricated,and the dynamic performance tests are carried out under sinusoidal excitation with different frequencies and amplitudes.The hysteretic characteristics of damping energy dissipation device are studied,and under sinusoidal excitation with the same frequency and amplitude,the damping force increases with the increase of the relative displacement of inner and outer tube.The ultimate damping force reaches 178kN under sinusoidal excitation with frequency of 0.5Hz,and the damping energy dissipation device meets the design requirements,has symmetry of tension and compression and stabile damping force.The hysteretic characteristics of self-centering variable damping energy dissipation brace are studied,and the brace exhibits a full similar flag shaped hysteretic curve,and the sliding force is lower than 200kN,so the performance is better than the existing self-centering energy dissipation braces.The energy dissipation capability increases with the increase of the excitation frequency and amplitude,the ultimate bearing force of brace increases with the increase of the excitation amplitude,and the residual deformation energy dissipation ratio decreases with the increase of the excitation frequency and amplitude.The brace has symmetry of tension and compression.The dynamic performance test results of self-centering variable damping energy dissipation brace are in good agreement with that of finite element numerical simulation.The relative errors of ultimate bearing forces corresponding to the maximum displacements are not more than 6.0%,and the relative errors of energy dissipation in half cycle of tension or compression are not more than 9.0%,so the accuracy of finite element numerical simulation are verified.