The Behavior Of Concrete-filled Narrow Rectangular Steel Tubular Columns Subjected To Eccentric Compression

The compressive strength of the core concrete can be significantly improved because of the restraining effect of external steel tubes in CFST members.At the same time,the internal concrete can prevent the concave deformation of the outer steel tube and improve its local bearing capacity.Compared with ordinary reinforced concrete structures,CFST have the advantages of high bearing capacity and good ductility,and CFST has gradually been widely used in super high-rise buildings and large-span buildings.Rectangular concrete-filled steel tube members not only have the characteristics of high plastic deformation capacity,good ductility,excellent seismic performance and large bending stiffnessaround strong axis,but also overcomes the inconvenience of design and construction which often appears in circular CFST members.In the existing studies,the aspect ratio of rectangular concrete filled steel tube is limited to 2 or less.However,at present,with the rise of fabricated civil buildings,CFST with large aspect ratio(CFNRST)has begun to be used for special-shaped columns or shear wall structures.CFNRST columns were fabricated and tested to failure under combined compression and bending.The test parameters included aspect ratios,slenderness ratios and eccentricity ratios.The ultimate failure mode of the CFNRST columns is overall buckling and local buckling of steel tubes were observed in this experiment.The ultimate loads of CFNRST columns decresse with increase of slenderness ratios and increase with decrease of eccentricity ratios.Its ductility increases with increase of slenderness ratios and decrease of eccentricity raios.It is worth noting that the restraining effects of steel tubes diminish with increase of aspect ratios and the effect is rather weak when aspect ratios are greater than 2.5.The restraining effects also decrease with increase of eccentricity ratios,which is the main reason of the decrease of ultimate loads.In this paper,abaqus is used for finite element analysis of eleven CFNRST columns in the experiment.The analysis results are compared with the test results to verify the validity of the finite element model.Then the displacement load curves of each specimen,the stress cloud diagrams,the strain cloud diagrams that are difficult to measure were obtained by establishing a large number of finite element models,and the main reaserch parameters included aspect ratios,slenderness ratios,eccentricity ratios,the yield strength of steel,and thichness of steel.Finally,this article introduced the detailed calculation methods of the ultimate load of CFST under combined compression and bending proposed by Eurocode-4,AISC360,GB50936,CECS159 and Han Lin-Hai.The ultimate bearing capacity obtained by the above specifications and design methods are compared with experimental values and FE values.Based on the methods of AISC360 and Han Lin-Hai,the refined calculation formula was proposed,and the modified calculated values were in good agreement with experiment values.