Slenderness-based design criteria to allow for the plastic analysis of tubular beams

Abstract

The present paper focuses on the rotational capacity of H.S.S. steel sections; in particular, the influence of local buckling is accounted for by means of a new generalized cross-sectional slenderness parameter, which is used to characterize the cross-sectional rotational capacity, and, by extension, the available deformation capacity.Careful shell modelling of hollow section beams in bending was used, the numerical models being previously carefully validated against more than 50 bending tests. Extensive F.E. studies were consecutively performed, including many parameters such as various material grades, load and support arrangements, length-to-height ratios, etc. Specific attention was paid to the introduction of initial geometrical (local) imperfections, as they were shown quite influential on the rotation capacity.The paper then analyses the numerical results and points out the various influences of height-to-width ratio, shear, moment gradient, yield stress and length-to-height ratio on the available rotational capacity. In a second step, the rotational capacity demand vs. stability criterion is detailed, and related to the proposed generalized cross-sectional slenderness, which is shown to be more appropriate than the b/t ratios usually proposed in design codes. Finally, code-ready recommendations for new ways of allowing for plastic analysis in practical design following the proposed approach are given.