Study On Performance Of Concrete Filled Steel Tube With Outer Steel Reinforced Concrete Stub Columns Under Pression

A new type of concrete-steel composite member is proposed in the paper, concretefilled steel tube with outer steel reinforced concrete column, based on reviewing plentifuldomestic and foreign researches on concrete-steel composite columns and analying theshortcomings of existing composite members. It is the evolution and development of thiscomposite column based on steel encased concrete column and core steel-tube reinforcedconcrete column developed in recent years. It has better properties than existing compositemembers. Especially, the locations of the tube and angle steel lead to effectively improvethe shearing, bending, torsion and bearing capacity of column components, improve theductility and tenacity and make it have good mechanical performance. Mechanicalperformances of the specimens proposed in present paper under axial load and eccentricload had systematically been studied by means of testing research, numerical caculationwith FEM and theoretical analysis.Firstly, 6 concrete filled steel tube with outer steel reinforced concrete stub columnshad been designed and tested, 3 under axial compressive loading and 3 under eccentriccompressive loading. Observation and research had been carried out for the specimens onvertical load-vertical strain relations, horizontal deformation, macroscopical deformationcharacteristics, failure mechanism and failure modes. Observation and research had beencarried out for the specimens on harmonization of steel tube, angle steel and concretetogether deforming during loading. Also, distribution of the longitudinal stain on thesection and ductility had been carried out for the specimens.Secondly, finite element analysis models were set up for concrete-filled steel tubularstub column subjected to axial load, steel encased concrete stub column subjected toeccentric load and the specimens tested in the paper. Nonlinear finite element method(FEM) was available by comparing testing results with numerical results. Diferentparameters influenting on the mechanical propertis of the columns were studiedsystermatically and primary parameters were draw out. Plane cross-section assumptionwas affirmed. Thirdly, the basic assumptions and calculation formula of load capacity andcomposite stiffness of the composite column in axial compression were presented, basedon testing research and numerical research and considerring the primary parametersinfluenting on the mechanical propertis of the column, which were expressed in formaccordant with reinforcement concrete structure code. The calculated results agree wellwith the experimental results.Finally, the basic assumptions and calculation formula of load capacity of thecomposite column in eccentric compression were presented, based on testing research andnumerical research and considerring the primary parameters influenting on the mechanicalpropertis of the column, which were expressed in form accordant with reinforcementconcrete structure code. The calculated results agree well with the experimental results.