Buckling of Inelastic I-Beams under Uniform Moment

Many different theoretical models have been proposed for the flexural-torsional buckling of inelastic steel beams under uniform moment. These models are considered and what is argued to be a more accurate model is proposed, which is based on the tangent modulus theory of buckling, which uses the strain-hardening moduli for the inelastic material, and which accounts for residual stresses. The predictions for this model for a W 8 x 31 beam are compared with those for the previous models and the relative significance of the assumptions are determined. It is found that the critical moment of the beam is not very sensitive to the assumptions concerning the moduli of the inelastic material, but that the effects of monosymmetry induced by the residual stresses should be accounted for. The most important assumptions are found to be those of the magnitude and distribution of the residual stresses, which cause significant variations in the strength of the beam.