Cold-formed steel lipped and plain angle columns with fixed ends

• Significant global post-buckling on fixed lipped and plain angle columns examined.
• Warping fixity impact highlighted through eigen and finite element analyses.
• For lipped angles a new global column curve including post-buckling developed.
• For plain angles post-buckling accounted for by a reduced global-flexural curve.

The objective of this study is to explore the significant post-buckling reserve in global buckling that has been observed in tests on cold-formed steel angle columns, and to provide design guidance for locally slender cold-formed steel lipped and plain angle columns with fixed end boundary conditions. Global buckling modes are generally regarded to have no post-buckling reserve, and indeed all column design curves, including those used in North America for cold-formed steel columns limit the strength to 0.877Pcre (where Pcre is the global buckling load) or lower. However, tests conducted on cold-formed steel angles by Young (2004,2005) [1] and [2] demonstrate capacities significantly in excess of Pcre – an observation usually reserved for local-plate buckling modes, which due to transverse membrane resistance are known to have significant post-buckling reserve. In this work, specific attention is paid to the impact of end boundary conditions, with emphasis on warping (longitudinal) deformations. Utilizing nonlinear collapse analysis with shell finite element models, and existing testing, alternatives to current design methods are explored. New design procedures are recommended for strength prediction of cold-formed steel angle columns with fixed end boundary conditions.