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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: Recent investigations of square hollow section (SHS) metal tubes with externally bonded carbon fibres have shown significant increases in the axial capacity and mean crushing load, compared with the metal SHS. The composite metal–fibre tubes employed carbon fibre reinforced polymer (CFRP) matrix layouts of two and four layers of carbon fibres. In this paper the same sized two and four layer CFRP SHS were manufactured independent of the metal SHS, and the axial capacity and crushing behaviour were determined experimentally. Four different tube sizes were tested, resulting in tube width to thickness ratios between 32 and 144. A photogrammetry system was employed to accurately determine the buckling and post-buckling behaviour. It is shown that the capacity and mean crush load of the composite metal–CFRP SHS exceed the sum of those for the individual metal SHS and CFRP SHS, by up to 1.8 times. This composite action results from the bond between the metal and the carbon fibres, and the mechanics with respect to buckling, capacity and crushing is discussed. The strength of metal, composite metal–CFRP and CFRP tube walls are determined using the effective width approach, and are shown to compare well with the experimental results. [Copyright &y& Elsevier]

Abstract: Carbon fibre-reinforced polymer (CFRP) strengthening of structures has been gaining increasing interest, traditionally applied to concrete structures, and more recently applied to metal structures. Epoxy bonding of carbon fibre to metal has been successfully employed for strengthening structures loaded under static and impact loads. In this paper the metal–fibre bond is investigated under impulsive loads by the application of explosives to fully clamped solid aluminium beams. It is shown that the use of bonded CFRP to metal structures that undergo large plastic deformations is advantageous, since the full strength of the carbon fibres is utilised as a result of the large strain field produced by the plastic deformation in the metal. The experimental results show that a significant amount of energy may be absorbed by the layer of carbon fibres bonded directly to the metal, however subsequent carbon fibre layers suffer from interlaminar debonding mechanisms as a result of shock spalling that reduce their efficiency. A theoretical method is developed whereby the energy absorbed by the carbon fibres may be determined, and the remaining explosive energy is absorbed by the plastic deformation of the metal. Fibre efficiency factors for multiple fibre layers and dynamic effects are introduced and are shown to produce reasonable agreement with the test results. [Copyright &y& Elsevier]

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: Composite steel–carbon fibre reinforced polymer (CFRP) tubes combine the benefits of the stable, ductile plastic collapse mechanism of the steel and the high strength to weight ratio of the fibre/resin composite, to form a composite tube with high energy absorption capability. This paper presents experimental results of square hollow section (SHS) composite steel–CFRP tubes subjected to axial impact. A number of different steel SHS geometries and two different matrix layouts of the CFRP are investigated. The dynamic results are compared with quasi-static results of composite steel–CFRP SHS and dynamic results of steel SHS and CFRP SHS. It is shown that the crashworthiness properties of load uniformity and specific energy absorption of the composite steel–CFRP tubes exceed those of the steel-only and CFRP-only tubes. An additional advantage of the CFRP application technique is that the CFRP may be retro-fitted to existing steel tubes, and the energy absorption capacity is shown to be markedly improved by such application. A theoretical method to calculate the dynamic mean crushing load which includes the effects of strain-rate is shown to compare well with the experimental results. [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: The reinforcing effect of externally bonded composite materials in the ultimate response of steel structures is introduced and the principal variables discussed. Composite beams of carbon fibre reinforced polymer (CFRP) sheets and steel circular hollow steel sections (CHS) are considered in this study. The investigation aims to quantify the contribution of the external reinforcing system to enhancing the strength characteristics of the thin walled steel section. An analysis of the ultimate bending strength of composite steel-CFRP CHS tubular beams which accounts for material properties and fibre orientation is outlined. The variations in the elastic and yielded regions around the section are examined. The provided results demonstrate that the ultimate load can be increased satisfactorily by adding high-strength fibre sheets to the steel sections and externally reinforcing them. [Copyright &y& Elsevier]