Inelastic local and lateral buckling in design codes

The flexural requirements for plastic design of I-shaped steel sections in international codes of practice are inconsistent and provide misleading emphasis on local buckling as the primary strain-weakening effect. The loss of ductility due to simulated axial force occurring simultaneously with inelastic bending is also underestimated in these codes. A model is described to assess the maximum moment and available inelastic rotation prior to strain weakening due to the interactive local flange and web buckling and lateral-torsional buckling. The results of 44 tests on I-shaped steel beams under pure flexure and 14 tests on similar specimens under combined bending and simulated axial force are also described. The rotation capacities measured in these tests are examined in terms of standard local and lateral buckling parameters as well as the proposed model. The relative importance of the different parameters is assessed and the effectiveness of the theoretical model is demonstrated in the analysis of these experimental results.