The application of plastic flow theory to inelastic column buckling

• A theory is presented to describe inelastic buckling of a compressed strut.
• The model is consistent with the principles of (incremental) plastic flow theory.
• The theory accounts for flexural, torsional and flexural-torsional modes.
• The model shows excellent correlation with the experiment.

The paper presents a theory of inelastic column buckling which is consistent with the principles of plastic flow theory. The theory accounts for flexural, torsional and flexural-torsional modes. While the use of the tangent modulus to describe inelastic flexural buckling has been common place for a long time, efforts to comprehensively unite the torsional and flexural-torsional modes with the principles of plastic flow theory have so far been hampered by the ‘plastic buckling paradox’. New theoretical developments presented in this paper provide a way to achieve this goal. The solution hinges on the derivation of the inelastic shear stiffness while considering an infinitesimal solid element embedded within the column at a stage immediately past the point of buckling.The proposed inelastic column theory is verified against selected experimental data pertaining to aluminium and stainless steel columns of various cross-sections. Particular attention is paid to the torsional buckling problem of the inelastic cruciform section column.