Research On Mechanical Behavior Of High Strength Concrete-filled High Strength Square Steel Tube Slender Columns Under Axial Compression Based On Steel Above Q550

In recent years,concrete-filled steel tube has been widely used in various building structures due to its high bearing capacity,high stiffness and good anti-fire and anti-earthquake performance.Concrete filled steel tube with square section is gradually popularized and applied in practical engineering because of its convenient connection and flexible design of joint structure.With the increasing demand of high-rise,super high-rise and long-span structures for material strength,high-strength materials are widely used in the field of civil engineering.Based on the above requirements,this paper puts forward the composite structure of high strength concrete-filled high strength square steel tube slender columns,and analyzes its mechanical properties under axial compressionIn this paper,high strength concrete-filled high strength square steel tube slender columns under axial compression were tested and studied.Taking steel yield strength and slenderness ratio of members as variable parameters,the failure mode,load-deflection curve,lateral deflection curve,load-strain curve and poisson ratio curve of the specimens were sorted out and studied.Based on the experimental data of the mechanical properties of the specimens,the finite element analysis of the specimens is carried out to prove the correctness of the finite element modeling method proposed in this paper.The stress analysis of the steel and concrete in each stage and the change of the interaction between them in the process of failure are carried out by means of the verified model building method.The influences of concrete strength,steel yield strength,steel ratio and slenderness ratio on the bearing capacity,ductility and concrete contribution rate of composite members are explored.The results show that the mechanical process of the composite members can be divided into four stages: elastic stage,elastic-plastic stage,plastic strengthening stage and descending stage.Except for the specimens with small slenderness ratio which have the same strength failure as the short column,the other specimens all quit the work because of buckling failure.The corner area of the members is the strongest area of interaction between steel tube and concrete during the failure process.And the contact stress between them decreases with the increase of slenderness ratio.When the slenderness ratio of the specimen exceeds the limit slenderness ratio,elastic instability failure of the component occurs because the material can not fully play its properties.With the increase of steel yield strength and steel content,both the bearing capacity and ductility coefficient of components increase,while the contribution rate of concrete decreases.The initial stiffness of members is not affected by steel strength,but the increase of steel content will increase the initial stiffness.With the improvement of concrete strength grade of components,the initial stiffness,bearing capacity and contribution rate of concrete increase,but the ductility coefficient of components begins to decrease.The slenderness ratio of components is negatively correlated with the initial stiffness,bearing capacity and concrete contribution rate,while The influence of slenderness ratio on ductility coefficient is different.Finally,after fitting the experimental data with a large number of finite element simulation data,the method of calculating the stability bearing capacity is deduced by combining the unified theory of concrete-filled steel tube,and it is in good agreement with the test value and the finite element simulation value.In this paper,in order to explore the limit slenderness ratio of instability failure,the change range of slenderness ratio of high-strength square steel tube high-strength concrete middle long column specimens with high-strength materials is reduced.And the interaction between the two materials in the failure process is studied,which provides the basis for the limit of slenderness ratio of compression members in practical engineering design.Based on the above research results,a formula for calculating the stability bearing capacity of the composite member is proposed.