The axial capacity of thin-walled cold-formed open sections prone to distortional buckling

Abstract

Unlike columns, which bow out and collapse soon after a critical buckling load is reached, thin plates have a stable post-buckling behaviour, and so their failure load is materially higher than their buckling load. This characteristic makes members composed of thin plates very suitable for use in lightweight structures. When a thin-walled member which consists of a system of connected thin plates is subject to an axial load, the member may develop local, torsional, flexural buckling modes acting independently or in a variety of combinations. Whether buckling occurs in individual plate components, or as a system of connected plates, it will cause a reduction in the stiffness of the member, and hence a lower load carrying capacity is expected. Cold -formed, singly-symmetric, lipped channels, which are typical of members composed of thin plates, are prone to such behaviour. But owing to the introduction of edge stiffeners in the webs of the channel, another buckling mode is likely to come into play. This is known as distortional buckling, and its effect on the axial capacity of the channel forms the basis of this investigation. Although distortional buckling, like local buckling may cause premature overall buckling, it does not necessarily exhaust the load carrying capacity of the structural component.