Basic Mechanical Behavior Of Circular Steel-tube-confined Concrete-filled Steel Tube Short Columns

This thesis carried out a systematic experiment and finite element study on the basic mechanical properties of steel-tube-confined concrete-filled steel tubes(TCFST).At home and abroad,concrete-filled-steel-tube(CFST)and tubed concrete(T-C)had been studied systematically,and many improvements had been put forward in view of their shortcomings.While retaining the advantages of CFST and T-C,TCFST also makes up for the disadvantages which are composed of concrete-filledsteel-tube,outer steel tube and intermediate sandwich material.In this thesis,the mechanical properties of T-CFST were studied by experimental research and finite element method,which provided a theoretical basis for further researches.In this paper,17 groups of 34 short columns were designed to test the mechanical properties under axial compressive loading.Axial bearing capacity,the failure modes and axial load-vertical deformation relations were obtained.The specimens were compared and analyzed in the same steel ratio,which contains T-CFST,CFST,T-C,concrete-filled steel tubes-Bar(CFST-B),concrete-filled steel tubes-Steel(CFST-S),tubed reinforced concrete(T-RC)and tubed steel reinforced concrete(T-SRC).Different steel ratio of inner and outer tubes about T-CFST in the same steel ratio has been also compared and analyzed.Finite element analysis of ABAQUS was employed to develop the model to simulate the behavior of T-CFST columns under axial compression.The correctness of model and the reliability of finite element analysis had been verified.This thesis analyzed the behavior of T-CFST in different end stiffening forms and the rule of stress variation along vertical axis.Based on the finite element analysis mode,parametric studies were then carried out to explore the factors that influence the basic mechanical properties,and then get the formula.Section strength mode was developed to obtain the axial load-vertical deformation relations and stress-strain relations.Based on the load-vertical deformation relations,the typical phase had been divided.And then it analyzed the influence on the behavior of CFST from the outer steel tube.Extensive parametric studies were carried out to numerically investigate the behavior of section strength mode under axial compression.And then it analyzed the influence on stress of different parts.