Stub column response in light of local vs distortional buckling

The objective of this paper is to study the effect of distortional buckling on typical stub column testing used by industry to determine the effective area of cold-formed steel members under compression. Testing standards such as AISI S902 are intended to determine the effective area of stub columns experimentally; however, other failure modes such as distortional buckling or premature failure at the ends of the specimens can potentially occur prior to cross-section local buckling, and therefore the effective area could be underestimated. This can result in underestimating the capacity of longer compressive members in the design of real structures, where the overall capacity of the cross-section could be knocked down due to local-global buckling interaction. An experimental study on lipped channels and rack sections with relatively low distortional buckling capacity, compared to local buckling capacity, has been conducted at the Thin-Walled Structures Laboratory in Johns Hopkins University to shed light on the effect of other failure modes on the calculation of the effective area. Different end conditions including bare, intrack, welded, clamped, and also different means of artificially postponing the distortional buckling are examined experimentally, and practical recommendations have been provided on how to conduct experiments to get a more realistic effective area in stub column testing.

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