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Abstract Increasing awareness of environmental concerns is leading a drive towards more sustainable structural materials for the built environment. Natural fibres such as flax and jute have increasingly been considered for fibre-resin composites, with a major motivation for their implementation being their notable sustainability attributes. This paper is part of an ongoing effort by the author to demonstrate the structural properties of primary structural elements and members fabricated from natural fibre composites of flax and jute. Previously the structural properties of flat plates, plain channel sections and channel sections with complex stiffeners were investigated under pure compression. This paper presents investigations of channel sections with complex stiffeners under pure bending. A series of sixteen channels with varying geometries, complex stiffener arrangements and composite thicknesses were tested in pure flexure. Material tests indicated that the mean tensile elastic stiffness and strength values were 6386 MPa and 55.1 MPa for flax, and 6941 MPa and 62.1 MPa for jute. The experimental results indicated that flexural failure of the channel sections was governed by tensile fracturing. The ultimate moment capacities varied from 1.043 to 1.501 kNm for four-layered composites, and 2.184 to 2.511 kNm for six-layered composites. The analytical models predicted the experimental ultimate moment capacities well, with a mean and coefficient of variation of the test to predicted ratio of 0.97 and 0.06, respectively. Finite element models used progressive damage analysis via stress-based damage initiation models and damage evolution laws, to replicate the tension fracture failure mode of the channels. The numerical models predicted the experimental ultimate moment capacities well, with a mean and coefficient of variation of the test to predicted ratio of 0.99 and 0.06, respectively. [ABSTRACT FROM AUTHOR]

Public concerns about the environment, climate change, energy consumption and greenhouse gas emissions have placed increasing demands for the use of sustainable materials in the built environment. Natural fibres such as flax, jute and hemp have recently been considered for fibre-resin composites, with a major motivation for their implementation being their notable sustainability attributes. However, many studies have noted the relatively modest mechanical properties of natural fibre composites. Despite this, a recent paper by the author demonstrated that the compression strength of flat plates and plain channel sections may be suitable for light structural applications. This paper presents the geometric optimisation of channel sections via the inclusion of complex web, flange-edge and flange-interior stiffeners. It is demonstrated that the inclusion of geometric stiffeners restricts the development of local buckling, creating less slender channel sections with greater compression strength. Compression strengths are compared with steel and timber wall stud strengths and shown to be suitable for residential building applications. The combined plain channel and stiffened channel experimental data covers a broad range of section slenderness values, and design models are developed to predict their compression strength. [ABSTRACT FROM AUTHOR]

Natural fibres such as flax, jute and hemp have been utilised for thousands of years, however have only recently been considered for fibre-resin composites. A major motivation for such an application is their superior sustainability attributes compared with traditional building materials. Population rise continues to place increasing demands for new infrastructure. Meanwhile, public concerns about the environment, climate change, energy consumption and greenhouse gas emissions, place increasing demands for the use of sustainable materials in infrastructure. While there is a wealth of knowledge in the materials aspects of natural fibre composites, relatively few studies have investigated their potential for structural applications. This paper presents an experimental and analytical study of natural fibre composite plates and channel sections consisting of flax, jute and hemp fibres and subjected to pure compression. The intrinsic mechanical properties are shown to be relatively modest. However, the buckling and post-buckling responses are shown to be stable, the ultimate condition is reached in a stable and predictable manner, and failure ensues in a gradual and ductile process. These characteristics show promise for the use of natural fibre composite sections in light structural applications such as in the residential and light commercial markets. Additionally, the analytical effective width mechanics model shows promise for use as a design technique for estimating their compression strength. [ABSTRACT FROM AUTHOR]

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 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]