Study On Axial Compressive Behavior Of Concrete Filled Q690 Steel Tube Short Column

As the industry progresses and develops,the force forms of building structures are becoming more and more complex,and high-strength concrete filled steel tubes gradually emerge to meet higher-strength force requirements.High-strength concretefilled steel tube is a composite structure formed by using high-strength steel instead of ordinary steel to strengthen the lateral restraint of the concrete,thereby enhancing the strength of the core concrete and improving its brittleness;at the same time,the concrete also provides an internal support for the steel tube.It delays the local buckling of the steel pipe due to instability in the compression process,or causes the local buckling of the steel pipe to occur after the peak load.However,compared with ordinary steel,high-strength steel brings higher strength and at the same time reduces the overall ductility of the component.In order to explore the restraint effect of the core concrete or the restraint mechanism of the steel pipe and the influence on the bearing capacity of the Q690 steel when the square steel tube is used as the square steel tube under the state of the axial load of the square concrete-filled steel tube short column,this paper conducts experimental research and data analysis.,Finite element simulation verification and theoretical analysis.The following specific researches have been carried out on the mechanical properties of Q690 square concrete-filled steel tube short columns under axial compression:（1）22 short columns of Q690 high strength square steel tube concrete filled steel tube were designed and manufactured,and the static load axial pressure test was carried out.In the test,the failure form,bearing capacity,ductility and hoop action of steel tube on core concrete are analyzed and compared with the two parameters,namely,the ratio of width to thickness and the strength of core concrete.The results show that the ratio of width to thickness is the main factor affecting the ultimate failure of Q690 short column under axial pressure.The ultimate failure form of specimens with width thickness ratio less than 40 is ring drum failure,and the specimens with width thickness ratio greater than or equal to 40 are local external drum failure.The bearing capacity of the test piece is mainly determined by the nominal load,which is the sum of the steel tube section bearing capacity and the core concrete bearing capacity.Therefore,the bearing capacity is mainly affected by the material strength and the section area of the test piece.Under a certain width thickness ratio,the bearing capacity will be larger with the increase of the strength of the core concrete;the ratio of width to thickness or the ratio of steel or the coefficient of hoop only determines the bearing capacity The size of force increase is the size of the constraint action,and the ratio of width to thickness determines the ductility to a certain extent.With the decrease of the width thickness ratio,the ductility of the specimen is better.（2）The model of short column of square steel tube concrete filled steel tube is established by using ABAQUS.Firstly,the material properties and the corresponding relationship between stress and strain are determined according to the material performance test data of steel.The material properties of concrete are also obtained by material performance test.The stress-strain relationship is based on the constitutive relation proposed by Professor Ding faxing.For the selection of steel pipe element types,the shell element and solid element are compared,and there is no obvious difference;for the division of the mesh,after many attempts,the corner refinement method is used to divide the mesh and the size of the grid is determined.The results of the test are compared with the simulated results,including the peak load and the peak strain.Finally,the influence of the width thickness ratio on the failure of the short column of Q690 square steel tubular short column is verified by the stress cloud diagram simulated by the software.The finite element simulation is in agreement with the experimental results.（3）The ultimate bearing capacity of Q690 high strength square steel tubular short column under axial compression is calculated by the specification and regulations.It is proved that the steel tube has the restraint effect on the core concrete under axial compression.The traditional constraint mechanism is compared with that of Zhou.The difference between them is the proportion of effective constraint area to the total crosssectional area.Finally,based on the existing research results,the formula of bearing capacity of high-strength square concrete-filled steel tubular short column is given.The formula is based on the actual strain and is suitable for the case of local bucklin g or the steel pipe is not fully yield in the limit state,so as to provide reference for the engineering application of the composite structure.