Major axis in-plane buckling resistance of I-section beam-columns under moment gradient

The inelastic second-order resistance of I-section beam-columns under arbitrary loading cases of one-directional bending is mainly dependent upon two factors, namely the direction of bending and the contribution of the web and flanges to the section moment of inertia in the plane of bending. Based on the concept of an approximate method of the evaluation of inelastic second-order resistance of beam-columns presented by the authors elsewhere, the objective of the present study is to develop the model parameters representing functions for accounting an approximate inclusion of distributed plasticity effects of plastic zones (stress redistribution along the member length) and within the member most stressed section (stress redistribution across the most stressed section depth). The model parameters for major axis bending are assessed for narrow flange I-section beam-columns (symbol I is used for the narrow flange section identification) on the basis of results obtained from a number of FEM simulations based on an accurate shell modelling technique and using Abaqus software. The concept of equivalent geometric imperfections is applied in compliance with the so-called Eurocode's general method in order to include globally the effect of geometric and material imperfections. The resulting model parameters evaluated for I-section steelwork elements being laterally and torsionally restrained are compared with those developed elsewhere for hot-rolled wide flange HEB section members subjected to both compression and bending about the major principal axis. Additionally, results are compared with those obtained in previous studies and those of Eurocodes interaction criteria based on Methods 1 and 2. Concluding remarks with regard to the in-plane buckling resistance of double-tee section beam-columns are presented.