Research On Behaviour Of Concrete Filled Double-skin Steel Tubular Columns Subjected To Pure 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. The cross-section of the outer and innersteel tube are various, such as circle, square, rectangle and some others. One kind of CFDSTsection tubes was studied in this paper, that is, the outer steel tubes are circular hollowsections (CHS), while the inner steel tubes are CHS.The pure torsional behavior of concrete filled double-skin steel tubular columns is thebasis of the behaviour of CFDST subject to compression-torsion, bending-torsion,compression-bending-torsion and compression-bending-shearing. Behaviour and mechanismof concrete-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 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.(2) Six concrete filled double-skin steel tubular columns and one double hollow tubeswere tested under pure torsion. The primary parameters in the tests were nominal steel ratioand hollow section ratio, and the phenomena and data of the tests were analysed in detail.(3) Torque-angle relationship curves of concrete filled double-skin steel tubular columnssubjected to pure torsion were analyzed by finite element software ABAQUS. The numericalresults are compared with the experimental results. The calculated results were in goodagreement with experimental data, the reliability of finite element model was verified. Workmechanism on the composite columns was analyzed at three aspects: Failure modes of thecomposites, stress distributions of steel and concrete and interactions between steel andconcrete.(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, etc. Finally, practical calculation methods for pure torsionalcapacity were put forward, which can serve the engineering design.