Research On Mechanical Behavior Of High Strength Concrete Filled High Strength Square Steel Tube Based On Q550 Under Pure Bending

There are many advantages on concrete-filled steel tube(CFST),such as high bearing capacity,good plasticity and toughness,excellent fire-resistant performance,good economic benefits and easy construction,etc.It has been applied in many practical projects.Nowadays,many scholars at home and abroad have done a lot of in-depth and detailed theoretical and experimental research on the working performance and stress mechanism of CFST,and the research results have been quite mature.However,there are few reports about the mechanical properties of concrete filled steel tubular structures with double high strength materials,so it is necessary to carry out a series of experiments.In this paper,the mechanical properties of four high-strength concrete filled high-strength square steel tube under pure bending members made of steel above Q550 are studied by using the parallel research method of experiment and finite element analysis.The failure mode of the members and core concrete,load-deflection curve,load-strain curve,sine half-wave curve and plane section assumption verification curve are obtained.By choosing appropriate constitutive relation between steel and concrete,establishing element type and boundary conditions,and using simulation software ABAQUS to establish finite element model equivalent to test members,numerical simulation is carried out,and the obtained finite element simulation results and test results are compared to check the applicability and correctness of the finite element analysis model.According to the results of finite element simulation,the stress distribution law of steel tube and concrete and the change law of contact stress in the whole process of stress are analyzed theoretically.The flexural rigidity of test and simulation members is compared with the code calculated values of GB50936(2014),AISC-LRFD(2010),EC4(2004)and AIJ(2008),and reasonable suggestions are given.The influence of different parameters on the bearing capacity and flexural rigidity of members is studied.Finally,based on the existing formula,the bearing capacity calculation formula of high-strength concrete filled high-strength square steel tube under pure bending members for steel above Q550 is obtained through data fitting.The results show that the whole specimen is damaged by bending and shows good ductility in the whole experiment process.The cracks of the core concrete are evenly distributed in the pure bending section and the concrete is crushed at the local buckling of the steel tube.The maximum cracks have penetrated into the compression area,and the core concrete breaks along the through cracks.The bending moment-curvature curve can be divided into three stages: elastic stage,elastic-plastic stage and strengthening stage.When the bending moment reaches 0.7-0.8 times of Mue,the steel tube in the tension zone will yield,and when it reaches 0.8-0.9 times of Mue,the steel tube in the compression zone will yield.The increase of steel yield strength,steel content and concrete strength can improve the bearing capacity of the component,but the change of concrete strength has little effect on the improvement of the bearing capacity of the component;the flexural rigidity of high-strength concrete filled high-strength square steel tube under pure bending increases with the increase of steel content,while the change of concrete strength and steel yield strength has little effect on it.The calculation method of flexural rigidity in Japan AIJ(2008)can be used to the high-strength concrete filled high-strength square steel tube under pure bending.The calculated results of bearing capacity of high-strength concrete filled high-strength square steel tube under pure bending are close to the test results and the dispersion is small.Therefore,the formula is recommended to calculate the bearing capacity of high-strength concrete filled high-strength steel tube under pure bending.