Research On Mechanical Behavior Of High-Strength Concrete Filled High-Strength Square Steel Tube Subjected To Pure Bending

Concrete filled steel tube(CFST)has the characteristic of high bearing capacity,good plasticity,good toughness,good economic performance,fire resistant and convenient construction.The CFST is one of the steel-concrete composite structure which has been widely used in practical engineering.The scholars all over the world have carried out a comprehensive study on the CFST,however,the report of the research about high-strength concrete filled high-strength square steel tube(HCFHST)which used high-strength materials instead the ordinary steel and concrete are still less.In this paper,a comprehensive analysis was presented on the mechanical behavior of HCFHST subjected to pure bending by the test and finite element analysis methods.The test prepared a total of 6 specimens which divided into two groups that each one of them were the steel tube wall thickness of 4mm,5mm and 6mm.The test used third point loading method,then observed the failure mode and study the mechanism of the bending members.The ABAQUS was used to do the finite element analysis,than adjusted the constitutive modes,boundary conditions and meshes to make the simulation results fit well with the test results on failure mode and load-displacement curves.Based on the deep research of the test and simulation,the moment-curvature relationship,the distribution of steel stress and strain,the distribution of concrete stress and strain,bearing capacity of each component and the changing rule of the neutral axis were studied.Moreover,analyzed the influence of the bearing capacity,stiffness and ductility index by different steel ratio,yield strength of steel tube and compressive strength of concrete.Examined the calculation formula of flexural bearing capacity by different codes which included GB50936(2014),EC4(1994),AIJ(1997)and AISC-LRFD(1999).Then derived a formula to calculate the bearing capacity for the HCFHST.The study showed that the high-strength concrete worked well with the high-strength steel under bending moment.The bending moment-curvature relationship can be divided into elastic stage,elastic-plastic stage and strengthening stage.The bearing capacity of the HCFHST increased with the increase of steel ratio,steel yield stress and concrete compressive stress.The flexural stiffness and ductility also increased with the increase of steel ratio.The EC4(1994)code offered a suitable formulation for calculating the bearing capacity of the HC.FHST by a comprehensive analysis.The test data of' flexural bearing capacity verify the validity of the derived formula.