Research On Mechanical Behavior Of High-strength Concrete-filled High-strength Square Steel Tubular Stub Columns Under Axial Load

Concrete-filled steel tube columns(CFST)have better bearing capacity,ductility,economy and construction of fast speed over conventional reinforced concrete columns,and have been applied in many high-rise buildings,Bridges and factories.High-strength concrete has poor ductility.The core high-strength concrete filled in the high-strength tube can improve the compression strength and compression deformability.The in-filled high-strength concrete can also prevent the high-strength steel tubular from local buckling.The research of high-strength materials has decades of history.However,there is little report on the research of high-strength concrete filled high strength steel tubular column.These all need further developing and perfecting.The constitutive relations of composite structure materials were analysis by comparing the analysis results.Finite element analysis software ABAQUS is used to create CFST models with proper materials constitutive model,element type,suitable contact model,boundary conditions and loading mode.Three groups of axial compression short column were researched by experiment.Test results fit well with the finite element analysis results.Then the fail models,bearing capacity,deformation,confined effect between concrete and steel tube,load ratio,concrete stress field and stress field of steel tubular was analysis based on the finite element and experiment results.Bearing capacity design indicators during the various stages of the force is deduced.Finally,the finite analysis and experiments results are compared with design codes.The test results show that:five phases include elastic phase,elastic-plastic phase,hardening stage,decline stage and stable stage for the whole axial load process are proposed.The ductility of the components is increased with the increase of confined effect.The confined effect began at the elastic stage and changed with the changing of steel tube and concrete stiffness,and mainly concentrated at the corner of concrete core.The capacity of the components is increased with the increase of steel radio,concrete strength and steel strength.The stiffness is increased with the increase of steel radio.The ductility is increased with the increase of confined effect.Component failure modes tend to shear failure with the increase of steel strength and decrease of steel radio.The derived load bearing strength design formula can well calculate elastic modulus,elastic strength,yield strength,tangent modulus and ultimate bearing capacity of axial compression column.The bearing capacity formula of the EC4 can better agreement with experiment results.