Study On Seismic Performance Of Dampers With Replaceable U-shaped Steel Plates

A steel seismic damper with replaceable U-shaped steel plates is proposed in this paper,which is composed of three parts:energy dissipating element,force transfer element and constraint element.This damper makes full use of excellent and stable energy dissipating property of U-shaped damper and the construction of this damper absorbs and draws lessons from the bucking-restrained brace.Compared with the existing damper,this damper makes it a reality that can be detected,repaired and replaced rapidly after the severe earthquake on the premise of the low cost.To study the seismic performance of the damper,this paper has carried out pseudo static low-cycle loading test,theoretical analysis and finite element simulation which was carried out by using finite element analysis software of OpenSees.According to the low-cycle loading tests of seven full-scale damper with single-layer replaceable U-shaped steel plates specimens,hysteresis performance,energy dissipation performance and failure modes were studied.Besides,parameters such as the thickness of U-shaped steel plates,the length of plateform,the loading scheme and so on were adopted as test parameters to explore their influences on the seismic performance of this damper.Test results show that:(1)All damper specimens can obtain full hysteresis curves and display stable and excellent energy dissipation performance.The energy dissipation coefficient come up to 3.0;(2)The steel damper show that significant cyclic hardening may occur during low-cycle loading;(3)The plastic damage of the damper concentrates on U-shaped steel plate,which means that rapid restoration and replacement of the damper after a major earthquake can be achieved;(4)With the increase of the thickness of U-shaped steel plates,the strength of this damper increases prominently;(5)The yield region on the U-shaped ateel plates will concentrated when the length of plateform is too short.The strength calculation formulas of the damper with single-layer replaceable U-shaped steel plates are put forward through theoretical analysis,which mainly include yield strength and ultimate strength calculation formulas.Comparisons between the results of the calculation formulas and the experimental results show that they are in good agreement which verify the applicability of the formulas.Based on the residual plastic strain of U-shaped steel plate after cold bending,it is found that the initial residual strain caused by the processing of U-shaped steel plate can be effectively reduced if the U-shaped steel plate can be divided into some layers,and the ductility of the damper can be improved.So the damper with replaceable multi-layer U-shaped plates was put forward,and the low-cycle loading test was carried out on three full scale specimens,and the influence of the multi-layer U-shaped steel plate on the seismic performance of the steel damper was discussed.The test results show that;(1)All specimens can get full hysteretic curve and energy dissipation coefficient can reach about 3.0,which shows that the number of layer of U-shaped steel plates and the edge of U shaped plate of inner layer will not affect the hysteretic energy dissipation performance of the damper;(2)Under the low-cycle loading test,the internal U-shaped steel plate is the most prone to crack.(3)On the premise of the same thickness of U-shaped steel plate,the number of layers of U-shaped steel plates has great influence on the strength and stiffness of the damper,the more layers the U shaped steel plate is divided,the smaller strength and stiffness of the damper are achieved.(4)the theoretical formula of the yield strength and ultimate strength of the damper with single-layer U-shaped steel plates is still suitable for the dampers with multi-layer U-shaped steel plates.The numerical simulation on the performance of the steel seismic damper with replaceable U-shaped steel plates is carried out by using finite element analysis software of OpenSees.The comparisons of the simulation results with the experimental data shows that the model can fit the hysteretic behavior of the damper very well,which verify the correctness of train of thoughts that the damper is equivalent to a rod and the parameters in the constitutive model are all equivalent parameters and this model can be adopted to further research and development.