Research On Hysteretic Performance Of Overlapped K-joints Of Steel Tubular Structure Stiffened With Concrete Filled In Chord

Steel structure materials which have characteristics including light weight,high strength,good ductility and hysteretic behavior showed remarkable advantages in aspect of earthquake-resistance of engineering structures,and also become one of the most important forms of building structure.As an important part of steel tubular structure,joint is also a key part for structural energy consumption,The research on joint performance is the foundation for research and development of steel tubular structure.Compared with the static performance of steel tubular joints,the research on hysteretic behavior of steel tubualr joints is few,especially the research on the hysteretic behavior of reinforced steel tubular joints with concrete filled in chord is still in the initial stage.Based on this,this paper carry out a research on the seismic performance and failure mechanism of the reinforced steel tubular K-joints with concrete filled in chord though experiment.A total of 6 overlapped K-joints of steel tubular structure are tested though quasi-static experiment,moreover,make a comparison and analysis between quasi-static test data and results from finite element analysis.The main research work is as follows:(1)stiffened overlapped K-joints model is established by ANSYS in this paper.Weld simulation is introduced into the K-joints model though pre-analysis before test,then,To Prepare for the loaded test of specimen,the key parameters are determined,the static performance of joints is analyzed,and the geometry parameters of K-joints specimens are determined.(2)Quasi-static test research of reinforced K-joints.6 reinforced overlapped K-joints of steel tubular structure have been designed.Dynamic low-cyclic axial load is applied on two brace ends though servo actuator,and the failure mode of the node is investigated.The experimental results show that the main failure mode of the unreinforced joints is the buckling of the chord wall,and the reinforced joints with concrete filled in chord shows tensile rupture on chord wall and accompanied with slight buckling of the compression tube.By comparing the two types of failure modes,it can be concluded that the failure mode of the joints can be changed by the reinforcement of concrete filled in chord,though which the local buckling of chord is controlled and the ultimate capacity of the joints can be improved effectively.(3)Quantitative evaluation of hysteretic behavior of overlapped K-joints with concrete filled in chord.Based on the test results,the hysteresis analysis of the reinforced overlapped K-joints shows that the unreinforced overlapped K-joints and the reinforced overlapped K-joints perform good hysteresis behavior,which can meet the seismic requirements of the structure.The reinforcement of joints with concrete filled in chord can limit to the plastic development of the joints to a certain extent,which reduces the ductility and hysteresis performance,but increases the stiffness of the joints,which can effectively increase the ultimate capacity of the specimen.In addition,by comparing the two different reinforcement methods,it shows little different in hysteretic performance,which indicating that fly ash concrete can be a good alternative to traditional concrete used for local reinforcement of steel tubular structure.(4)Finite element analysis of hysteresis of Reinforced overlapped K-Joints.The finite element analysis software ANSYS is used to analyze the hysteresis performance of the joints.Compared with the quasi-static test,the joints failure mode is consistent with the experimental results.The hysteresis curve agrees well with the experimental results,but the ultimate capacity is little higher than experimental value.The finite element software can be used to make parameter analysis of the joints specimen.