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Abstract: Inelastic design methods allow for larger application of loads on sections than elastic design methods, due to the redistribution of yield stress through the depth of the section. Sections that can reach the full plastic capacity and maintain it for sufficient rotation are considered applicable for plastic mechanism design, resulting in more economical structural solutions. Cold-formed steel channel sections are used extensively in portal frame structures in agricultural and light industrial/commercial applications, structures well suited to plastic design, however may currently only be designed elastically. To address this limitation in design standards, experimental and numerical analyses on the inelastic bending capacity of cold-formed channel sections are performed, and design rules to account for such behaviour are developed. Design rules are prepared using the hot-rolled steel specification methodology of classifying a section as compact, non-compact or slender (according to the Australian Standards) and Classes 1, 2, 3 and 4 (according to the European Standards). Proposals for the Australian standard are shown to provide accurate and reliable capacity predictions for cold-formed steel channel sections whose bending capacity exceeds the elastic limit. [Copyright &y& Elsevier]

Abstract: The behaviour of thin steel plates fall into three general classes, unstiffened (no edge-stiffener), stiffened (adequate sized edge-stiffener) and partially stiffened (inadequate sized edge-stiffener). When used in cold-formed steel sections they may elastically buckle when subjected to either uniform compression or stress gradient. There are thus six possible combinations of element class and loading condition. All except the class of partially stiffened elements under stress gradient has been investigated experimentally, and design equations developed. This paper presents experiments of edge-stiffened plates under stress gradient, where the edge-stiffener size was increased from zero to a size sufficient to create a stiffened element. Edge-stiffener types investigated are simple lips and complex lips. Design solutions for partially stiffened elements under stress gradient using the effective width concept are presented. A generalised effective width design model is developed to account for all classes of elements under any loading condition. [Copyright &y& Elsevier]

Abstract: The aim of this paper is to investigate the inelastic bending capacity of cold-formed channel sections, and provide design rules to account for such behaviour. An extensive experimental and analytical analysis of 42 cold-formed channel sections in three different geometric categories is conducted, including simple channel sections, channel sections with simple edge stiffeners and channel sections with complex edge stiffeners. The sections were cold-formed from G450 steel with nominal thickness of 1.6mm, and varying theoretical buckling stresses ranging between elastic to seven times the yield stress. The results of the pure bending experimental investigations show that current international cold-formed steel specifications are conservative, for channel sections with low slenderness values. The experimental results are used to propose revisions to current international cold-formed steel specifications. [Copyright &y& Elsevier]

Abstract: With the advent of flange edge stiffeners and higher-strength steels producing thinner structural sections, additional complexities in buckling modes and their interactions has arisen. A number of authors have demonstrated that the use of flange edge stiffeners may result in the interaction of buckling modes, which may be detrimental to the strength of the section. However, the exact behaviour of such interactions and how they may be accounted for in design is not yet fully understood. One reason for this has been the lack of sufficiently detailed data of the transverse buckling deformations, which may involve displacements in different buckling modes and with different relative magnitudes. This paper presents the results of channel sections with simple flange edge stiffeners tested under pure compression. A 3D photogrammetry system was used in order to accurately capture the full-surface transverse buckling deformations of the flanges and webs. The detailed buckling results are used to describe and explain the fundamental behaviour of flanges and webs, particularly with respect to interactions of buckling modes. Comparisons of the test results with the recently modified effective width method and the direct strength method are discussed. [Copyright &y& Elsevier]

Abstract: Recent developments in the section approach to the design of cold-formed steel structures have led to design rules that address sections with edge-stiffened flanges, where the edge stiffeners give rise to the distortional buckling mode. However, the element approach to design (effective width method) remains unable to deal with this mode of buckling, and has been shown to routinely provide unconservative design capacities for such sections. This paper provides design rules for edge-stiffened elements that may be used in conjunction with the existing element approach in specifications, in order to determine the capacity of sections with edge-stiffened flanges in compression. The design rules are developed from an extensive analysis of the fundamental behaviour of plates simply supported on three sides with the remaining (longitudinal) edge stiffened with an edge stiffener. When used in conjunction with the effective width method they are shown to provide excellent agreement with tests of sections that contain edge-stiffened flanges in compression, thus removing the unconservatism in current specifications. [Copyright &y& Elsevier]

Abstract: Carbon fibre reinforced polymer (CFRP) strengthening of structures has been gaining increasing interest, traditionally in application with concrete structures, and more recently in application with steel structures. This paper presents experiments and plastic mechanism analysis of steel square hollow section (SHS) tubes strengthened using externally bonded CFRP, deforming in an axi-symmetric collapse mode under quasi-static large deformation axial compression. The fold formation process of the stub column was such that the flat sides formed the well-known roof mechanism. The collapse proceeded progressively by folding about concentrated hinge lines and yielding of the four corners. An expression for the plastic collapse axial load was obtained by equating the total energy absorbed in bending and yielding to the external work carried out during deformation of the composite tube. The predicted instantaneous post-buckling and mean collapse loads are shown to compare well with the experimental results. [Copyright &y& Elsevier]

Abstract: Cold-formed open steel sections are comprised of component plates termed stiffened elements (webs) and unstiffened elements (flanges). The local buckling and post-local buckling behaviour of sections may be determined from the behaviour of the component plates. Much research effort has documented the theoretical elastic local buckling of plates and sections, however until recently few experimental studies have been reported on the local buckling and post-local buckling behaviour of unstiffened plates. This paper presents experimental and numerical studies of unstiffened plates and sections that contain them in both compression and bending, and in particular analyses the mechanism that provides post-buckling strength. It is shown that, as with stiffened elements, the mechanism is the post-local buckling redistribution of stress, however unlike stiffened elements this redistribution can occur to such an extent that tensile stresses commonly form in axially compressed slender elements. The stress distributions at ultimate are compared with current international cold-formed steel specifications. [Copyright &y& Elsevier]

Thin-walled compression members are commonly designed on the assumption that the loaded edges remain straight. Under this assumption, tensile stresses develop in the most flexible parts of the component plates at advanced local buckling deformation, and thus are assumed to be ‘anchored’ at the ends. However, current design rules for plate elements, such as the Winter formulae, are partly based on tests in which the load was applied by use of rigid platens that did not permit tensile stresses to develop. There exists an apparent inconsistency between the assumption of straight loaded edges and the use of a design curve calibrated from tests in which the loaded edges of component plates may not have remained straight.This paper addresses this apparent inconsistency by comparing finite element solutions for the conditions of straight loaded edges and loading by use of a contact surface between the plate edge and a non-deformable rigid body end platen, where there is no constraint for the plate edge to remain in contact with the rigid body. Solutions are provided for a single half-wavelength of unstiffened and stiffened plate elements simply supported along three and four edges, respectively. The effect of multiple half-wavelengths is also investigated, as is the effect of interaction between elements in practical sections comprising stiffened and unstiffened elements. [Copyright &y& Elsevier]