Keywords: cold-formed sections, portal frames, built-up sections, local plate buckling, distortional buckling, overall buckling, finite element analysis, codes.

Cold-formed sections buckle locally and distortionally in combination with the overall buckling of the member. When these sections are incorporated into a portal frame structure, this combination of buckling modes affects the overall buckling behaviour of the portal frame. The objective of this paper is to study the effect of local and distortional buckling on the overall behaviour of portal frames. The portal frames studied have a span of 10 m and an eave height of 3 m with a roof pitch of 1:10. Two frames are studied the first with one intermediate interconnector at the midpoints of the column and rafter members and the second with two intermediate interconnectors at the third points of the column and rafter members. Three section thicknesses are studied for each frame. A nonlinear finite element analysis is performed for each frame. The critical frame section is designed according to the Egyptian Code of Practice (ECP) allowable stress design (ASD) and load and resistance factor design (LRFD), as well as, the American Iron and Steel Institute's North American Specification for the Design of Cold Formed Structural Members (AISI S100). Unity factors are calculated and the factor of safety or reduction capacity factor as obtained using the finite element analysis is determined.

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