On the mechanics of local-distortional interaction in thin-walled lipped channel columns

The objective of this paper is to present and discuss numerical results concerning the geometrically non-linear behaviour of thin-walled lipped channel columns experiencing local-distortional (L-D) interaction that will shed fresh light on the mechanics underlying this coupling phenomenon. These results, obtained through Generalised Beam Theory (GBT) elastic post-buckling analyses, provide the evolution, along given equilibrium paths, of the column (i) deformed configuration, expressed in modal form, (ii) relevant displacement profiles, and (iii) modal participation diagrams. Taking full advantage of the GBT modal features, it becomes possible to unveil the most relevant behavioural/mechanical aspects associated with the occurrence of L-D interaction. Particular attention is devoted to the structural interpretation and explanation of the quantitative and qualitative differences exhibited by the column post-buckling behaviours associated with (i) “pure”/individual local and distortional behaviours and (ii) the occurrence of L-D interaction stemming from either the closeness between the local and distortional critical buckling loads (“true L-D interaction”) or from a secondary bifurcation phenomenon (“secondary distortional or local bifurcation L-D interaction”). The columns analysed exhibit (i) the aforementioned different types of L-D interaction, (ii) two support conditions, namely fixed (mostly) or pinned end cross-sections, and (iii) several critical-mode initial geometrical imperfection shapes.