Research On Mechanical Behavior Of High Strength Concrete Filled High Strength Square Steel Tube Columns Based On Strength Q550 Subjected To Bi-axial Eccentric Loading

Concrete-filled steel tube structure(CFST)has been widely used in practical projects because of its many advantages,such as high strength,large section modulus,good plasticity and toughness,good durability,convenient construction and good seismic performance.Many scholars have carried out a detailed study on its mechanical properties.High strength concrete has the advantages of high compressive strength,good corrosion resistance,good impermeability and frost resistance,and small creep.Compared with the ordinary strength steel,the application of high strength steel can reduce the cross-section size and the total weight of the structure,correspondingly reduce the welding workload,so as to improve the fatigue life of the structure,reduce the amount of antirust,fireproof and other coatings,and improve the economic effect of the building.High-strength concrete became more obvious due to its continuous brittle failure.Therefore,it can give full play to the advantages of high compressive strength and avoid the disadvantages of brittle failure by placing it under the constraint of highstrength square steel tube.In this paper,the mechanical properties of high strength concrete filled high strength square steel tube(HCHSST)stub columns subjected to bi-axial eccentric loading were studied by the method of experiment and FEA.17 CFST columns with different steel yield strength,load eccentricity and slenderness ratio were tested under biaxial compression,including 6 short column test members and 11 middle long column test members.The failure mode,ultimate bearing capacity,load-mid section deflection curve,load-other section deflection curve,and load-strain curve of the outer surface of the steel tube were obtained.On the basis of experimental study,ABAQUS finite element analysis software was used to simulate the biaxial eccentric compression column of HCHSST.The correctness of the finite element model was verified by comparing the finite element simulation with the test results.Combined with the test and finite element simulation results,the stress distribution of square steel tube and core concrete,the load-bearing situation of each component,the change rule of contact stress between steel tube and concrete were further analyzed.On the basis of this analysis,the mechanical mechanism of the component and the influence of changing different parameters on the mechanical properties of the specimen were further analyzed.Finally,based on the experimental and finite element analysis results and the existing theoretical research,the bearing capacity calculation formula for the HCHSST two-way eccentric columns was obtained by data fitting.The results show that the whole process of biaxial eccentrically loaded short columns can be divided into the following five stages: elastic stage,elastic-plastic stage,plastic strengthening stage,descending stage and gentle stage.The whole process of biaxial eccentrically loaded long columns can be divided into four stages: elastic stage,elastic-plastic stage,plastic strengthening stage and descending stage.With the increase of the compressive strength of concrete cube,the initial stiffness of the member was increased by a small margin,and the ultimate bearing capacity basically increased linearly.With the increase of steel yield strength,there was no effect on the initial stiffness of the component,and the ultimate bearing capacity of the component was basically linearly increased.With the increase of eccentricity,the initial stiffness of members decreased in turn,and the ultimate bearing capacity decreased gradually.With the increase of steel ratio,the initial stiffness and ultimate bearing capacity of the members increased linearly.With the increase of slenderness ratio,the initial stiffness and ultimate bearing capacity of members decreased in turn.Through the analysis of a large number of finite element simulation results and experimental results,combined with the calculation model of the unified theory of concrete filled steel tube,the calculation formula of bearing capacity was derived and compared with the test value,which was less discrete,so it was recommended to adopt.