L. Hollaway

An experimental study of the influence of plate end anchorage of carbon fibre composite plates used to strengthen reinforced concrete beams

Abstract Carbon fibre reinforced polymer (CFRP) materials are well suited to the rehabilitation of civil engineering structures due to their corrosion resistance, high strength-to-weight ratio and high stiffness-to-weight ratio. Their application in the field of strengthening is envisaged to expand due to the vast number of bridges and buildings in need of strengthening. In order to apply these materials effectively, it is necessary to understand the behaviour of members strengthened with externally bonded composite plates, one aspect of which is the response to the installation of anchorage at the ends of the plates to resist plate separation from the beam. A number of 1.0 m long plated beams were tested in four point bending and as cantilevers to demonstrate that the structural benefit of plate end anchorage diminishes as the shear span/depth ratio of the beam increases. Under a low shear span/depth ratio (3.00 in the present work), the anchorage improves the composite action between the plate and the beam, giving rise to greater structural stiffness after yield of the internal rebars. This beneficial influence can be achieved using a bolted anchorage system which provides the same improvement in composite action as a large plate end clamping force generated by trapping the plate under the beam supports. Although the plate end anchorage has most structural benefit under a low shear span/depth ratio, it is recommended that anchorage be applied in every case until long term practical experience suggests otherwise.

The analysis of elastic-plastic adhesive stress in bonded lap joints in FRP structures

Abstract The majority of researchers who investigate the theoretical distribution of adhesive stresses in bonded lap joints assume that the adhesive behaves as a linear elastic material. While this assumption does provide useful information, for example, the intensities of stress concentrations and their locations, the results do not reflect the true stress distribution or behaviour at appreciable levels of loading. Practical joints using typical structural adhesives will incur considerable adhesive yielding as loading is increased to failure. The analysis must, therefore, include plastic yielding of the adhesive. This paper presents two analytical techniques, namely, the classical and finite element theories, which will be used to determine elastic-plastic adhesive stress distribution in bonded lap joints. The theoretical work will consider the single, double and tubular lap configurations having both similar and dissimilar adherends. Case studies will be presented to illustrate the development of adhesive yielding and to compare the different analytical techniques. The classical approach was found to be intractable to a closed form solution and consequently a numerical method was employed.

The analysis of elastic adhesive stresses in bonded lap joints in FRP structures

Abstract Numerous publications provide the closed form solution for adhesive stress distribution in bonded lap joints. However, in order to render these solutions tractable the authors invariably impose simplifications, one of the most restrictive being that the adherends are identical. This is unrealistic for bonded joints in most practical structures where a variety of dissimilar components may be assembled. This paper presents two analytical techniques, namely the classical and the finite element theories, which are used to determine the elastic adhesive stress distribution for the single, double and tubular lap configurations. The generality for dissimilar adherends is included. The governing differential equations obtained when using the classical approach necessitate a numerical solution and in this paper a procedure is described which uses the finite difference method. Example solutions are presented as case studies.

Optimisation of adhesive bonded composite tubular sections

Abstract The paper discusses a bonding technique for the joining together of tubular sections which are under axial loading. In particular the yielding of polymers was studied and the criterion which was eventually used in the analyses was a modification of the Von Mises one. The Paraboloidal criterion accommodates differences in tensile and compressive yield strengths and accounts for any dependence of yielding on the hydrostatic component of the applied state. The yielding behaviour of the thin layer of the adhesive epoxy resin was analysed and it has been shown that the prediction of the adhesive strength is affected by the progress of the yield. Comparisons between the Paraboloidal and the Von Mises yield criteria have also been applied to a modified tubular joint involving threads within the bonded region. It is suggested that the prediction of the stresses at yield, using the modified criterion have a greater credibility compared with those of the Von Mises.

Long-term static testing of an FRP prototype highway structure

Abstract In recent years it has become apparent that the labour and maintenance costs of highway structures fabricated from conventional constructional materials (i.e. steel and concrete) are rising, and therefore the whole life cost of these structures is being significantly affected. Highway structures manufactured from advanced composite materials provide a viable solution to reduce substantially both the labour and the maintenance costs, whilst providing structures that behave in accordance with the present British code of practice for highway structures. The principle objectives of the investigations were to undertake experimentally and to verify, where applicable, numerically the suitability of advanced fibre-reinforced polymer (FRP) composite materials manufactured in the form of box beams for use as highway structures. It was also important to research into any unique behaviour exhibited by the FRP structures while under test and to develop relevant theoretical models and formulae to characterize completely this behaviour. The composite box beam showed no signs of global deterioration and generally behaved as predicted; the short term stiffness of the beam measured at specific times during the test did not decrease to any extent. There was some local flexural cracking in the connectors at the position of the applied loads, but this can be eliminated by design. The creep and deflections of the beam at the end of the test were well within acceptable limits.

Vibrational analysis of a double-layer composite material structure

Abstract As new manufacturing techniques for glass reinforced polymers are developed and existing ones improved, new structural engineering design methods will become available for the construction industry to exploit. The most promising area currently is the pultruded double-layer skeletal fibre/matrix structural system. Considerable research effort has been directed towards design techniques and structural imperfections associated with those systems under static loading. This paper discusses the analysis of a particular type of double-layer skeletal structure, under dynamic loading and manufactured by the pultrusion method. Analytical and experimental techniques have been used in the analysis, and a discussion of these techniques is presented. It is concluded that, provided great care is taken in modelling the analytical system, good agreement between the two methods of analysis is obtained; it is necessary that mechanical properties of the material of the prototype are accurately determined.

Fabrication and analysis of fibre/matrix space structures

Abstract As new manufacturing techniques for glass reinforced polymers are developed and existing ones improve, new structural engineering methods will become available for the construction industry to exploit. The two most promising areas are those of the folded continuum and the double layer skeletal fibre/matrix structural systems. This paper describes the manufacturing procedures that are available for both these systems and discusses the design techniques and structural imperfections associated with the latter one. It is shown that although the skeletal systems are lightweight and the material has a low modulus of elasticity, the configuration is such that the overall deformations are well within the acceptable limits with the result that these systems will be serious competitors to the conventional skeletal ones.

About the modelling of laminated composites

Abstract Plane loaded laminated composites are modelled as a membrane, using the laminated plate theory, or as a layered three-dimensional body. This paper tries to find the assumption of the laminated plate theory which is responsible for most of the free edge errors. This is achieved by imposing each of the assumptions of the laminated plate theory separately on a three-dimensional model of a simple problem. To analyse that model, a two-dimensional method, which is suitable for this class of problem, is presented. Based on the findings, a new modelling technique for symmetrical laminated membranes is suggested.

Load Distribution in Two-Pinned Polymer Composite Joints

This paper describes some analytical investigations undertaken on a bolted joint for pultruded members which is under an axial load. The study involves an investigation of the load distribution in a joint employing only two pins. The problem is approached by determining the deformational behaviour of a composite plate subjected to loads applied through two pins using two-dimensional finite elements. Laminated plate theory and the rigid frictionless pin assumption are used.

A simple material model for unidirectionally aligned fibre reinforced composites

Abstract A material model for the nonlinear behaviour of composite materials is proposed. The model combines the linear elastic fibre properties with the nonlinear behaviour of the matrix in order to obtain the average properties of the composite. The interaction between the fibre and the matrix is considered using stress partitioning factors, which are based on the experimental behaviour of the material.