Mode interaction in thin-walled equal-leg angle columns

• Mode interaction effects in thin-walled equal-leg angle columns with intermediate lengths.
• Interaction between major-axis flexural-torsional and minor-axis flexural buckling modes.
• Determination of the less and most detrimental critical-mode initial imperfection shapes.
• Imperfection-sensitivity analyses of the column post-buckling behaviour and ultimate strength.
• Maximum elastic and elastic–plastic column failure load erosion due to interaction effects.

This paper presents and discusses numerical results, obtained through Ansys shell finite element analyses, dealing with the post-buckling behaviour (mostly elastic, but also elastic–plastic), ultimate strength and failure mode nature of fixed-ended and pin-ended thin-walled equal-leg angle steel columns with coincident critical flexural-torsional and minor-axis flexural buckling loads (i.e., experiencing very strong coupling effects between these two global instability phenomena) – for comparative purposes, columns that are buckling in pure flexural-torsional and flexural modes are also analysed. Since the main aim of the work is to investigate the column imperfection-sensitivity, the analyses concern otherwise identical columns containing initial geometrical imperfections with different shapes and amplitudes, combining the competing critical buckling modes – particular attention is paid to the sign of the minor-axis flexural component. The results reported consist of column (i) elastic equilibrium paths and the corresponding peak loads and deformed configurations and (ii) elastic–plastic collapse loads and mechanisms, making it possible to assess how they are influenced by the initial geometrical imperfections.