Strength, interactive failure and design of web-stiffened lipped channel columns exhibiting distortional buckling

• Web-stiffened lipped channel columns failing in distortional modes: interactive behaviour and failure.
• Experimental investigation, numerical simulations and the Direct Strength Method (DSM) design.
• Experimental and numerical evidence of local–distortional (L–D) interaction and failure load erosion.
• Numerical imperfection-sensitivity study: relevance of the initial imperfection local component.
• Performance assessment of existing/novel DSM design approaches against L–D interactive failures.

The paper reports experimental and numerical results concerning the post-buckling behaviour, strength and failure of fixed-ended cold-formed steel web-stiffened lipped channel columns that buckle in distortional modes. The experimental results, obtained from the tests carried out at The University of Hong Kong, (i) include initial imperfection measurements, equilibrium paths and failure loads and modes, and (ii) provide evidence of the occurrence of flange-triggered local-distortional interaction. After presenting and discussing a comparison between some test results and the values yielded by the corresponding Abaqus shell finite element numerical simulations, the experimental failure loads obtained in this work, together with additional data reported in the literature, are used to assess whether the available Direct Strength Method (DSM) design approaches are capable of predicting them efficiently (safely and accurately). It is found that this is not the case, mainly because of the fact that the mechanics of the flange-triggered and web-triggered local-distortional interactions are quite different. Although fairly good failure load predictions are provided by a new DSM design approach proposed in this work, further research is required on the mechanics of local–distortional interaction in web-stiffened lipped channel columns.