Study On Behaviour Of Concrete Filled Double-skin Steel Tubular Square Columns Subjected To Compression-torsion

Concrete filled double-skin steel tubular (CFDST) is a new type of composite structurefilled with concrete between two concentric steel tubes. It can offer many advantages, such ashigh bearing capacity, good plasticity and malleability, convenient construction, high fireresistance, high bending rigidity, light deadweight and so on. It can be used for The structureof the higher requirements for seismic performance and flexural stiffness, for instance,high-rise buildings,viaduct piers, Power transmission tower,wind power generation stent. Thecross-section of the outer and inner steel tube are various, such as circle, square, rectangle andsome others. One kind of CFDST section tubes was studied in this paper, that is, the outersteel tubes are square hollow sections (SHS), while the inner steel tubes are CHS. This kind ofCFDST section tubes can not only conducive to the connection of the beam-column joints,and it helps to prevent the inner tube partial flexion. This article studied the mechanicalproperties of its pure torsion and compression-torsion.The pure torsional and compression torsional behaviors of concrete filled double-skinsteel tubular columns are the basis of the behaviours of CFDST subject tocompression-torsion, bending-torsion, compression-bending-torsion andcompression-bending-shearing. The pure torsional and compression torsional behaviors ofconcrete-filled double-skin steel tubular columns were investigated in this paper includingexperimental and theoretical studies. Through the parametric analysis, the practicalcalculation methods for pure torsional and compression torsional capacity were developed.The main achievements were summarized in detail as follows:(1) The relevant researches were reviewed firstly. The finite element method and testprogram were selected for the behaviour analysis of concrete filled double-skin steel tubularcolumns subjected to pure torsion and compression-torsion.(2) A total of4concrete filled double skin steel tubes which were fabricated with circularhollow section (CHS) as inner and square hollow section (SHS) as outer skin and1concretefilled steel tube were designed and tested in order to study the mechanical properties underpure torsion. The parameter varied in the tests were nominal steel ratio and hollow sectionratio. A total of6concrete filled double skin steel tubes(SHS outer and CHS inner) and1concrete filled steel tube were designed and tested in order to study the mechanical propertiesunder compression-torsion. The parameter varied in the tests were slenderness ratio,axialcompression ratio and hollow section ratio. All the phenomena and datas of the tests wereanalysed in detail. (3) Torque-angle relationship curves of concrete filled double-skin steel tubular columnssubjected to pure torsion and compression-torsion were analyzed by finite element softwareABAQUS. The calculated results were compared with the experimental results. Thecalculated results were in good agreement with experimental data, the reliability of finiteelement model was verified. Work mechanism on the composite columns was analyzed fromthe following aspects: failure modes of the composites, stress distributions of steel andconcrete and the interactions between steels and concrete and so on.(4) Based on the finite element method, parametric analysis was performed on thebehaviors of Torque-angle relationships for the composite columns. The selected parameterswere the nominal steel ratio, the inner and outer tubes yield strength, hollow section ratio,concret compression strength, the ratio of the diameter and the thickness of the steeltubes,slenderness ratio and axial compression ratio. Finally, practical calculation methods forpure torsional capacity and compression torsional capacity were put forward, which can servethe engineering design.