Ultimate strength of horizontally curved I-girders with round concrete-filled tubular flange

Concrete-filled tubular flange girders (CFTFGs) are a composite member which replaces the flat-plate flange of the conventional I-girder with a concrete-filled tubular one. As a single axisymmetric girder, the bending, torsion, and warping geometric equations of curved CFTFGs, as well as the balance equations in and out of the plane, are coupled. These problems make it sophisticated to settle the ultimate strength of curved CFTFGs. Besides, the existing current design specifications do not involve a calculation method of the ultimate strength of individual curved CFTFGs. Therefore, the present study focuses on the ultimate strength and behaviour of curved round concrete-filled tubular flange girders (CRCFTFGs) under concentrated load at mid-span. Based on the verified finite element (FE) model, the elastoplastic behaviour of CRCFTFGs is analysed. Subsequently, the theoretical analysis model of CRCFTFGs is established, and the calculation methods of the elastic lateral-torsional buckling (LTB) moment and the full plastic bending moment on the cross-section of CRCFTFGs are proposed. The comparison between the theoretical and FE results indicated that they are in good agreement. Lastly, based on the ECCS formula and the theoretical analysis model of CRCFTFGs, the calculation formula of the ultimate strength of CRCFTFGs considering the effect of curvature is suggested. The accuracy of the presented formula is verified through comparisons with the FE and existing experimental results. The suggested formula for calculating the ultimate strength of CRCFTFGs can provide theoretical guidance for the code formulation.