Search

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]

Abstract: There is a large body of literature on the experimental behaviour of steel plates under a variety of loading and edge support conditions. Typically the longitudinal plates edges were either laterally restrained (stiffened) or laterally unrestrained (unstiffened). There are no such plate experiments reported in the literature of plates with a longitudinal edge stiffened with an edge-stiffener (partially stiffened). This paper presents 30 plate tests of plates simply supported on three sides, with the remaining (longitudinal) edge stiffened with an edge-stiffener. The edge-stiffener was increased in size from zero (unstiffened plate) to a size sufficient to create a stiffened edge (stiffened plate). Edge-stiffeners of an intermediate size resulted in partially stiffened plates. The behaviour of partially stiffened plates is fully documented with the aid of a 3D photogrammetry system, and the adequate size of edge-stiffeners required in order to create a stiffened plate edge are discussed. Edge-stiffener types investigated are simple lips, simple inclined lips and complex lips. Design procedures for partially stiffened elements previously inferred from numerical studies are shown to accurately and reliably determine the plate strengths, and further validate the procedure for use as a general strength approach in current international cold-formed steel specifications. [Copyright &y& Elsevier]

Abstract: Composite metal-carbon fiber reinforced polymer (CFRP) tubes combine the benefits of the high strength to weight ratio of the fiber/resin composite and the stable, ductile plastic collapse mechanism of the metal, to form a composite tube with high strength and energy absorption capability. This paper investigates the axial capacity and crushing behavior of square hollow section (SHS) tubes composed of composite steel-CFRP, stainless steel-CFRP and aluminum-CFRP. Experiments of tubes with different metal SHS geometries and two different matrix layouts of carbon fibers are described, and a general theory to predict the compression buckling, axial capacity, axial collapse and mean crush load of metal–fiber square tubes is developed and validated against the experimental results. It is shown that carbon fiber may be successfully externally bonded to metal SHS, and such application may be provided to improve the performance of existing structures, or to design new structures with enhanced strength-weight and energy absorption-weight ratios. Comparisons are made between the performance of the different types of metals, SHS geometries and carbon fiber matrix layouts. [ABSTRACT FROM AUTHOR]

Abstract: Carbon fibre reinforced polymer (CFRP) strengthening of structures has been gaining increasing interest, traditionally applied to concrete structures, and more recently applied to steel structures. This paper describes 20 experiments on short, axially compressed square hollow sections (SHS) cold-formed from G450 steel and strengthened with externally bonded CFRP. The SHS were fabricated by spot-welding and had plate width-to-thickness ratios between 42 and 120, resulting in plate slenderness ratios between 1.1 and 3.2. Two different matrix layouts of the CFRP were investigated. It is shown that the application of CFRP to slender sections delays local buckling and subsequently results in significant increases in elastic buckling stress, axial capacity and strength-to-weight ratio of the compression members. The experiments are an extension of a previous study [Bambach MR, Elchalakani M. Plastic mechanism analysis of steel SHS strengthened with CFRP under large axial deformation. Thin-Walled Structures 2007;45(2):159–70] in which 25 commercially produced SHS with plate slenderness values between 0.3 and 1.6 were strengthened with CFRP in the same manner. A design method is developed whereby the theoretical elastic buckling stress of the composite steel–CFRP sections is used to determine the axial capacity, and is shown to compare well with the 45 test results. A reliability analysis shows the method to be suitable for design. [Copyright &y& Elsevier]

Abstract: Particular structural forms such as circular tubular sections when under load may experience premature local buckling of the steel component, attributable to the thin-walled nature of the section. The use of high-strength advanced composite materials tends to accompany the minimum of structural weight, and is hence presently being assessed for effectiveness as supplementary external reinforcing materials. Composite beams of fibre-reinforced polymers (FRP) and steel, formed as tubular steel sections externally reinforced by thin-bonded carbon FRP (CFRP) sheets, exhibit many phenomena not found in conventional structural steel components, and these can have a marked bearing both on the behaviour of members composed of these materials and, by connotation, on the way in which such members are designed. The potential identification of CFRP reinforcement incorporated onto steel circular hollow section (CHS) beams has not been adequately explored, particularly in pure moment regions. This paper provides an experimental study consisting of CHS beams reinforced by CFRP sheets under pure bending. The role of the composite reinforcement is to interact with the enveloped steel component and to restrain the section to deform in a favourable fashion for strength enhancement. It is shown how these sections exploit the best attributes of both reinforcing fibres and steel, conferring greater strength to CHS beams made with thin-walled steel sections. The tests reveal that the strength of composite beams is influenced mainly by the amount of fibre reinforcement and the orientation of fibre skin. Also presented in this paper is an analytical method employing the modular ratio concept and considering the sectional slenderness limits of AS 4100 for evaluation of the strength of CFRP-reinforced CHS beams. [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: 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]

The current slenderness limits are significantly different in international design codes for cold-formed Circular Hollow Sections (CHS) under pure bending. This paper aims to use the Finite Element (FE) method to understand the behaviour of cold-formed CHS under pure bending and to propose new design rules. The model is calibrated by comparing its predicted load-deflection curves with previously published experimental data. In total, 21 specimens were modelled with diameter-to-thickness ratios ranging from 13 to 122. The current slenderness limits in the present international steel specifications were examined using the FE model and their suitability for cold-formed CHS is discussed. The effect of section slenderness on rotation capacity has been examined where the predicted variation of rotation capacity against section slenderness has been compared to the experimental results. A new equation for the amount of initial geometrical imperfection as a function of section slenderness has been developed and proposed for design purposes. The ovalisation deformation ratio and the critical strain at local buckling were determined and compared for compact, non-compact and slender sections. The progressive bending deformations of CHS at 10 critical steps have been presented and compared for the three cross sectional types, in particular at the maximum moment and bending rotation. In general, a good agreement has been obtained between the predicted strengths and ductilities using the current FE models and those of the experimental data of cold-formed CHS. • Using finite element method to determine the slenderness limit of cold-formed steel tubes and compared to the previous experimental results. • The effect of geometrical imperfections on the deformation cold-formed CHS has been examined. • The rotation capacity has been presented for CHS. • The ovalisation of compact, non-compact and slender section has been analysed. • The buckling mechanism has been analysed by using strain analysis, the critical strain at maximum moment has been determined and compared to the theoretical results. [ABSTRACT FROM AUTHOR]