Study On Static Behaviour And Analytical Theory Of Tapered Concrete-Filled Double-Skin Steel Tubular Members With Large Hollow Ratio

Recent development in structural engineering has heightened the need for tapered Concrete-Filled Double-skin Steel Tubular members with Large Hollow Ratio(LHRCFDSTs).To date,limited research has been reported on the structural behaviour of this kind of members.In this paper,the static performance and the ultimate capacity prediction method of tapered LHR-CFDST members under different loading conditions were systematically studied by means of experimental investigations,Finite Element(FE)simulations and theoretical analyses.The main work and the achieved outcomes include:(1)A series of static tests on the twenty-six tapered LHR-CFDST members subjected to different loading conditions including axial compressive load,torsional load,compression-torsion load,bending-torsion load and compression-bending-torsion load were conducted.The failure mode,the load-deformation relation and the strain distribution were investigated.The performance of members under different loading states and the influence of key parameters were preliminarily revealed.The applicability of current ultimate capacity prediction methods for tapered LHR-CFDST members was examined.(2)The FE models of tapered LHR-CFDST members were established and verified by test data.Then the behaviour of LHR-CFDST stub columns under axial compression was analyzed in terms of the axial force-axial displacement relation,the stress/strain distribution,the axial compressive force distribution and the steel-concrete interaction.The effects of parameters including tapered angle,hollow ratio and steel tubes’ diameter thickness ratio on the performance of columns were also investigated.(3)The mechanisms of tapered LHR-CFDST members subjected to the pure torsion load and the compression-torsion load were studied.The effects of tapered angle,hollow ratio,steel tubes’ thickness,strength of material and axial compressive ratio on the torquetorsional angle relations were analyzed through the validated FE model and the full-range behaviour of the members were summarized.Additionally,the stress-strain state,the internal force distribution and the steel-concrete interaction of tapered LHR-CFDST members under pure torsion and compression-torsion were investigated.Based on the analysis results,the torsional mechanism of the tapered LHR-CFDST member was revealed.(4)The mechanical properties of tapered LHR-CFDST columns under the bendingtorsion load and the compression-bending-torsion load were analytically studied by investigating the failure patterns,the load-deformation relations,the development of stress/strain and the interaction between the steel tubes and the sandwiched concrete.The influence of key parameters,such as tapered angle,hollow ratio,steel tubes’ diameter thickness ratio,axial compressive ratio and bending to torsion ratio,on the behaviour of columns was examined.The results showed that the columns have good ultimate capacity and ductility within the common range of parameters.(5)The theoretical models at the ultimate state of the tapered LHR-CFDST member under axial compression and pure torsion were established,respectively.Combined with numerical calculation and parameter analysis,the simplified methods for predicting the compressive capacity and the torsional capacity of the tapered LHR-CFDST member were proposed,respectively.Furthermore,the ultimate capacity correlative relations of tapered LHR-CFDST members under compression-torsion,bending-torsion and compression-bending-torsion load were parametrically studied and deeply analyzed.According to the results,the practical ultimate capacity prediction methods of tapered LHR-CFDST members under compression-torsion,bending-torsion and compressionbending-torsion load were proposed,respectively.The reliability of the proposed methods was verified by the experimental data and the numerical results.