Mechanical Behavior Of High Strength Concrete Filled High Strength Steel Tube Slender Column Under Axial Load

With the maturity of the theory research of concrete filled steel tube(CFST),it has been widely used in the civil engineering.Compared with the round concrete filled steel tube(RCFST),the square concrete filled steel tube(SCFST)doesn't have a good bearing capacity as well.But it has a lot of advantages such as large cross-section bending rigidity,easy to repair,and so on.In recent years,the SCFST has been studied in a lot of research work,and the application of it is increasing.High strength concrete has the advantages of high strength,high rigidity and good durability.High strength steel has the advantages of high strength,good welding performance and toughness.The combination of the two materials has the effect of amplifying the effect of the individual.Based on the experimental study of the High-strength Concrete Filled High-strength Steel Tube(HCFHST)columns under axial compression.The model of HCFHST is established by ABAQUS with reasonable material constitutive relation model.The finite element results are compared with the test results.Its failure mode,stress-strain curve,load deflection curve,the relationship between the load and the load bearing capacity and the ratio of the length are obtained.In this paper mainly research the stiffness,bearing capacity,ductility,failure mode through experimental study on.The optimal combination of two kinds of materials in HCFHST is studied.In the end,the application of the formula for the calculation of the bearing capacity of the HCFHST is compared and analyzed.The results show that the ultimate load carrying capacity of slender columns in HCFHST is linear with the increase of the slenderness ratio.And the limit slenderness ratio of HCFHST is85.45.The reason for causing changes of the stability factor lies in changing ultimate strain corresponding to ultimate bearing capacity of core concrete,instead of changing intensity of core concrete.For HCFHST under the axial compression members,the core concrete strength has little effect on the initial stiffness,but a greater impact on the ultimate bearing capacity.It is obvious to improve the ductility of the member.The yield strength of the steel tube has little effect on the initial stiffness and ductility of the members,but it has a great influence on the ultimate bearing capacity.The changing of steel ratio has obvious influence on the initial stiffness and ultimate bearing capacity.The ultimate bearing capacity of the member is increased with the increase of steel ratio in a certain range.And the optimal steel ratio is 0.1159 by finite element analysis.The calculation results of HCFHST are in good agreement with the measured values.For the middle columns,the calculation accuracy of the AISC is the highest.With the increase of the length,the calculated results of GB50936-2014 are the most accurate.The conditions for the optimal combination of the two materials is that the steel yield strain is lessthan the peak strain of the core concrete.