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Textile reinforced concrete (TRC) is a high performance cementitious composite using straight and parallel aligned fibers of suitable materials, e.g. ARglass and carbon, as continuous reinforcement in form of textiles. Textile reinforced concrete is usually used for thin concrete elements or as strengthening layers for concrete structures. Textile reinforced concrete shows a multi linear stress-strain-behavior with three distinct stages (uncracked, multiple cracking, cracking completed). The crack formation in textile reinforced concrete is significantly finer than in customary reinforced concrete. Therefore, not only the tensile strength of the concrete but also the total tensile load bearing behavior of the composite material textile reinforced concrete is of importance. The uniaxial tensile test presented here is a test method to determine the load bearing behavior of tensile specimens made of TRC. Bond characteristics of textile reinforcement can not be derived from this tensile test since this information could only be derived indirectly from cracking patterns. However, in textile reinforced concrete cracking is mainly controlled by transverse fibers which are typically present in textile reinforcement. For bond properties reference is given to the RILEM recommendation TDT A.2 (pull-out).

One of the main interest which concerns substitution of FRP (Fiber Reinforced Polymer) such as carbon epoxy composite by TRC (Textile Reinforced Concrete) for rehabilitation of existing infrastructures is its thermal stability and fire behavior. The first part is devoted to the description of experimental methodology developed by Si Larbi et al. for tensile characterization of TRC and prediction of ultimate resistance for different levels of temperature (20–600 °C). In the second part, the structural behavior of short concrete columns loaded under axial compression and confined by TRC is considered. Taking into account the design method proposed by Hamelin et al., the strength increase is estimated for different conditions of fire stability. Finally, we conclude on the interest of TRC reinforcements for steel concrete structures particularly in the case of accidental loading conditions such as fire or blast considering thermo-mechanical stability, gas toxicity and smoke opaqueness.

This paper analyzes the failure behavior of E-glass reinforced inorganic phosphate cement composites in tension and compression. The first part of the study experimentally evaluates the behavior of different composite systems resulting from three different manufacturing processes (hand lay-up, pultrusion and pultrusion/compression). Tensile and compression tests are performed on fiber orientations ranging from 0° to 90°, and the mechanical tests are analyzed in terms of failure strength and failure modes. The prediction of failure strength is approached using mechanical models found in the literature. The comparison of experimental and modeling results is unsatisfactory, confirming the necessity of establishing adapted fracture criteria. The second part of this paper concerns the establishment of a failure envelope based on the Tsai–Wu and Mohr–Coulomb criteria. The anisotropic nature of the composite is accounted for by the Tsai–Wu criterion, while the Mohr–Coulomb criterion allows for the modeling of the mineral matrix’s brittle behavior. The maximum stress criterion is also compared to the obtained envelope curves.

This experimental and numerical study is related to the repair and strengthening of reinforced concrete beams with TRC (textile-reinforced concrete) and hybrid (TRC + carbon and glass rods) solutions that are positioned relative to the more traditional ones such as the CFRP (carbon fibre-reinforced polymer) solutions. Beyond the good performances highlighted experimentally, especially in terms of bearing capacity and different failure modes (e.g., possibility to avoid peeling off), it is clear from this work that the TRC, despite its nonlinear behaviour (multi-cracking), does not allow a significant gain in ductility. From a numerical perspective using numerical modelling (smeared crack approach), the overall behaviour of beams reinforced with TRC (or the hybrid solutions) based only on the textile “efficiency factor” (or the average contribution of the filaments) as a calibration coefficient was found to be significantly satisfactory. Numerical modelling performed on all the beams also highlighted the fact that the axial stiffness of reinforcements (even in the case of a cracking material) governing the overall behaviour of beams could, at least in part, explain the observed failure modes.

The aims of this work are to assess the mechanical performance of textile reinforced concrete (TRC) in the shear repair of reinforced concrete beams and then compare it to more traditional solutions, such as CFRP (Carbon Fibre Reinforced Polymer), and to identify the local mechanisms of damage and failure of the repaired beams. Two types of implementation are considered: the hand lay-up in situ and the bonding of prefabricated plates. The results show that TRC performs well compared with CFRP and has qualitatively similar effects on the overall behaviour of the repaired beams. However, the contribution of the TRC is clearly stabilised, as shown by an operating model based on the truss analogy, which permits the systematic yielding of the transverse steel rebar. This stabilisation can be attributed to a localised TRC behaviour that depends on the implementation chosen and most likely on the rigidity of the interface (TRC mortar/substrate of the beam) or the interphase.

Over the last twenty years, composite materials, especially carbon epoxy, have developed as part of the repair and strengthening of reinforced concrete structures. This is mainly due to their very good mechanical performance as well as their easy implementation, which is fast and unobtrusive. However, composites also have a number of limitations that make the alternatives advantageous, for example their very high price, their incompatibility with sustainable development, and their very low efficiency ratio.

The objective of this paper is to analyse the feasibility of using composite beams made of high performance fibre reinforced mineral matrix as structural elements. The mineral matrix is an inorganic phosphate cement (IPC), in which E-glass fibres and fabrics are used as reinforcement. Post-tensioning was studied as a way to improve the bending and shear behaviour of beams. Longitudinal compression and 4-point bending tests were carried out on three types of beams: centrally, internally and externally post-tensioned. The validity of fundamental principles of post-tensioning technology was investigated by performing global and local analysis of the behaviour of these beams. The strain levels, corresponding to different thresholds of post-tensioning loads, were assessed by analysing strain superposition principles. The experimental results showed a reduction of the risk of cracking and limitations of the deflection and of the acting shear force. The post-tensioning generates a translation of the initial strain to the compression field and produces a linear strain distribution, as opposed to that of flexural strain. Moreover, in the case of external post-tensioning, it was possible to choose an adapted eccentricity of the tendon profile to optimise the effect of the post-tensioning on the deflection and on the acting shear force.

This paper presents an experimental approach to study the durability of FRP composites used in the civil/structural engineering. Carbon epoxy (carbon/EP) and carbon vinylester (carbon/VE) composites were considered for accelerated ageing (thermal, hygrometric, chemical, thermochemical, hydrothermal, freezing–thawing cycles, etc.) over 18 months. The accelerated ageing tests were selected to reflect the real operating conditions on natural civil engineering environment. The same composites were also subjected to environmental ageing to assess the effectiveness and the relevance of the accelerated exposure. Changes in tensile strength and viscoelastic response were evaluated through mechanical testing and Kinemat analysis. The design factors prescribed by the existing principle guidelines were applied to experimental measurements. The results revealed the presence of drawbacks inherent in these regulations based on a determinist approach.

Various aspects related to the durability of Fibre Reinforced Polymer (FRP) composites used in the rehabilitation, repair and strengthening of existing concrete structures were studied as a function of cure behaviour. The performance of these FRP-composites containing thermoset matrix and implemented under civil engineering conditions, is unstable and their properties will change over time due to their partial cure. The present work attempts to raise awareness about the characteristic changes of FRP-composites materials immediately after their ambient cure, while emphasizing the implication of such phenomena on the durability. Both glass transition temperature Tg and mechanical characterization tests were performed to identify the effects of curing on thermorheological and mechanical stability of the composites immediately after the implementation. The experimental results indicate that overall composite performance was sensitive to the cure conditions. The implication of this sensitivity on the durability of FRP-composites was addressed and clearly identified through accelerated and natural exposure tests which reflected the civil engineering environment.

While the development of TRC (Textile Reinforced Concrete) in recent years is undeniable, validated experimental protocols and standards are slow to take hold. By drawing judiciously from previous studies, this work aims to identify and propose contribution to direct tensile test for design purpose which is reliable, efficient and relatively easy to implement. The results obtained on the basis of a large series of experiments involving the laminating technique and the use of field measurements (photogrammetry measurement) have permitted the validation, based on five criteria (considered to be the most relevant), of the test protocol in a design context. The limitations of the protocol were identified, including the poorly reproducible nature of the initial zone and the impact of implementation defects (e.g. dissymmetry of reinforcement in the thickness of the TRC composite and the warping of specimens).

It is technologically possible to strengthen steel-reinforced concrete structures with externally bonded carbon–epoxy composites. The durability and performance of those reinforcements directly depend on the rheological behavior of the concrete–composite interface. We propose a methodology to evaluate the permissible shear stress of the interface, based on thermo-stimulated tensile shear tests performed on the interface, and taking into account the effects of time and temperature. Four polymers used for bonding were tested and a value for the permissible shear stress is proposed for each strengthening system.

The object of this paper is to propose an analytical model for the interpretation of the overall bending behavior of textile reinforced mineral matrix composite beams. The composite material is made from inorganic phosphate cement (IPC) and E-glass fiber reinforcements (unidirectional rovings and chopped strand mat). Experimental results related to the mechanical characterization of the composite material in tension and shear, as well as the analysis in four-point bending tests of different beams, were presented in a previous paper where it was noted that the shear characteristics of the composite material define the load-bearing capacity of the beams. In order to use the full potential of the composite material, it was necessary to strengthen the beams with braiding and wrapping. The analytical modeling approach, based on composite and classical beam theories, is used to reconstruct the overall behavior of beams, taking into account the mechanical characteristics of the different materials constituting the beams. The assessment of shear load-bearing capacity is therefore based on the contribution of each component of the beam: the composite material itself and the applied strengthening. The comparison of experimental results and analytical results shows that the proposed models fit well with the actual behavior.

Carbon–epoxy composite materials are of considerable interest for reinforcement, but they need to be improved and have constraints, particularly in terms of cost and criteria of sustainable development. Alternative materials like textile reinforced concrete (TRC) should be seriously considered as substitutes for traditional composite materials. This experimental study focuses on the mechanical feasibility of this type of solutions by comparing them with traditional solutions such as CFRP. The first comparative results are promising in terms of strength and stiffness. It can be established that, quantitatively, the materials have very similar behaviours, especially in the final stage. Finally, the Ritter–Morsch truss model can be used with sufficient accuracy for the evaluation of the tensile strength, by considering a non-uniform stress distribution along the shear cracks that leads to failure.

In this paper the mechanical behaviour in bending of textile reinforced mineral matrix composite beams is analyzed. Two types of textile reinforcement made in E-glass fibers are considered: unidirectional rovings and chopped strand mat (CSM). The mineral matrix is an inorganic phosphate cement (IPC) and presents the advantage to be non-alkaline. The beams are hollow with square cross section, they are realized by bonding together composite plates having the dimensions 200 × 10 × 1 cm . The plates are manufactured by pultrusion process, using the roving and the mineral matrix. In the first part of the paper we present the manufacturing process, and in the successive sections the mechanical characteristics of the composite itself in tension and shear are assessed. During the characterization tests, it has been emphasized that the shear behaviour is the weak point of the composite. Therefore, in order to enhance the mechanical behaviour of the beams, specimens have been strengthened using three types of reinforcement: internal reinforcement with struts, 3D external braiding and continuous wrapping by CSM reinforced mineral matrix. In the second part of the paper, the test in four point bending of four beams is presented. The analysis of the experimental results is governed by the search for a correlation between the phenomena observed at material level and those occurred during the tests of the structural elements.

This paper describes the behaviour of strengthened and unstrengthened reinforced concrete slabs, subjected to a single, specific, local, load at their centres. In the experimental stage, the influence of the reinforcement on the various slabs tested was analysed by studying their behaviour at failure and by making a bending stiffness analysis. In order to predict the mechanical behaviour of the slab, a model was developed to predict the value of the bending stiffness, the mid-span displacements and the strain on each material making up the slabs. The experimental results were compared to those of the model and there was good agreement.

Bonded composite steel–concrete bridges are an interesting alternative to traditional composite bridges with metallic connections. However, one cannot limit the bonding joint design to longitudinal shearing, although that remains important. It is important to consider the out-of-plane tensile stress which develops along the bonded joint and is caused by the transversal bending of the beam, especially in the case of twin-beam structures, and also the differential bending between the metallic profile and the concrete slab under concentrated load, which can cause brittle failures. This article aims, firstly, to model the behaviour of the adhesive lap joint of concrete/steel composite beams connected by bonding. De-bonding is caused by shear and peeling stress, which is calculated under local loading. Secondly a bi-axial failure criterion (shearing–out-of-plane tensile stress) in the bonded joint is established through the use of an original experimental procedure. Finally, it seeks to validate this criterion on a simply supported bonded composite beam of 3.3 m, which is subjected to a static load until failure, using a theoretical-experimental approach. The first results obtained are very encouraging and show that the established quadratic interaction criterion is well-adapted.

This study pertains to the experimental and theoretical behaviour of slabs strengthened by fibre reinforced polymer (FRP). The experimental results show that FRP significantly increases punching failure stress, resulting in a reduction of slab rotation around the loading column. The theoretical investigation presents a finite element model for the bending of strengthened slabs. The developed model considers the concrete as a 3D multi-layered non-linear material and explicitly takes into account the steel reinforcement and the FRP strips. The proposed model is then used to analyse the effects of a concrete cover on the reinforcement and repairs. In the analysed cases, the results show that an average reduction in the concrete shear modulus, between steel rod and FRP, of more than 30% leads to significant reductions of stress and slab stiffness.

Nowadays, reinforcing buildings or bridges against earthquake damage is a real technico-economic challenge. Composite materials applied by the wet lay-up method have been the main reinforcement technology for civil engineering structures since the 1990s. The research developed in this paper concerns seismic reinforcement. The main objectives are to evaluate CFRP’s contribution to mechanical and energetic performance and to the modification of the cracking pattern on short columns. During earthquakes, short columns undergo shear stress due to their low resistance to high imposed horizontal displacements. Eight short columns were tested; their longitudinal reinforcement was higher than the Eurocode 8 upper limit whereas transverse reinforcement was insufficient, in order to ensure shear failure. Seven were continuously or discontinuously reinforced by CFRP or GFRP. They were tested under a constant compression load combined with a horizontal quasi-static cyclic load. It was therefore possible to evaluate the efficiency of such reinforcement by measuring the gain in terms of load and ductility.

This paper deals with the analytical modelling of elastic stress state inside RTM-moulded braided composite cylinders under lateral compression. Taking into account the radial stresses, our modelling is based on the Fourier series development of the π-periodic symmetric loading, deriving from the Hertzian contact law. The experimental part describes the quasi-static delamination under lateral compression of RTM-moulded carbon–epoxy rings, made from braided two-dimensional (2D) tubular preforms and DGEBA-IPD resin. The theoretical part shows a mesoscopic computation of transverse shear stresses is needed in order to explain the locations of the brittle failures. We eventually introduce the notion of an equivalent virtual major crack occurring at a critical value of displacement in order to provide a simplified representation of crack onset and energy release.

High performance concrete reinforced by short metallic fibers has been recently developed. These materials are of particular interest for civil engineering thanks to their high compression performance and to their enhanced durability. The addition of short metallic fibers provides the opportunity to obtain a more ductile material with more resistance to tension. Nevertheless, the use of reinforcement is still necessary for structural applications [1] . This paper presents results obtained on SFRHP concrete beams using mixed steel–CFRP rebar. Five beams with steel rebar or mixed CFRP–steel reinforcement were designed according to Eurocode 2. The goal is to optimize the reinforced concrete (RC) beam design by combining different reinforcement types in order to use the fiber reinforced HPC most efficiently. The first beam specimen uses a non-fibrous HPC and constitutes a reference for comparison. The tests carried out upon an FRHPC beam and reinforced by steel reinforcing bars allow the assessment of the short fiber’s effect against the bending and the shearing stresses. It is shown that the presence of short metallic fibers in the concrete does in fact contribute to the equilibrium of the beam. The sum of the internal moments in the tensile zone is increased by 10%. For the last three beams, the effect of incorporating carbon fiber reinforced polymer rebar mixed with usual steel reinforcement is studied. It is shown that beams using mixed CFRP–steel rebar are able to achieve a bending stiffness comparable to the beams reinforced by traditional steel reinforcement (in the elastic stage). A 50% increase in the failure load is observed.

This paper presents an analytical model adapted to all FRP-confined concretes, including confined HPC. The development of this model is based on an experimental compressive behavior study using various concrete cylinders externally confined by carbon and glass FRP jackets described in part A of this paper. Different parameters such as the confinement level and the jackets mechanical properties are taken in to account. Proposed relationships allow to assess the ultimate capacity and the stress–strain mechanical relation of the confined concrete as a function of each materials parameters. Experimental results presented in the part A of this paper and those obtained by other authors are compared with the analytical results predicted with the described model. The stress–strain responses of all FRP-confined concrete obtained by the proposed model are in accordance with experimental data. The ultimate behavior is well predicted, for all confinement levels and all concrete types.

This paper presents an analytical and experimental investigation for evaluating the punching shear strength of two-way concrete slabs externally bonded by CFRP composite sheets. First, the punching failure mechanism and the parameters governing this failure mode are discussed and an analytical model for punching failure of reinforced concrete slabs developed by Menetrey [Synthesis of punching failure in reinforced concrete. Cement Concrete Compos 2002;24:497–507] is presented. Based on numerical simulation, this model allows the treatment of slabs considering the dowel effect contribution of steel reinforcement. The generalization of this model to the case of slabs externally bonded by CFRP laminates requires the consideration of biaxial behavior of composite sheets resulting from two-way slab boundary conditions. Finally, the theoretical extension is applied to predict the ultimate punching shear strength of eight slabs with several levels of CFRP reinforcement and designed to fail in shear. The results show good agreement between the predicted and experimental values.

This paper presents the results of an experimental investigation concerning the compressive behavior of concrete short columns externally confined by carbon and E-glass FRP jackets. The influences of different parameters such as the confinement level, the mechanical properties of the jackets and the compressive strength of the concrete core were studied. The results show that external confinement can significantly improve the ultimate strength and ductility of the specimens. The stress–strain response of confined concrete is bilinear: in the first linear zone, the behaviors of plain and confined concrete specimens are similar, whereas in the second pseudo-plastic branch, the behavior of confined concrete depends mainly on the jacket mechanicals properties. Test results demonstrate that the second part of (plastic) the stress–strain response depends on the jacket stiffness and that the ultimate strength of the jacket and the concrete strength are the most influential factors affecting the ultimate strength and strain of the confined concrete. Also, the study indicates that the confinement efficiency falls when the compressive strength of the concrete core increases.

A novel 3D braiding machine has been designed in order to produce high performance composites. Our objective is to establish the link between some of the main parameters governing the braiding process and the mechanical properties of layer-to-layer interlock 3D braided composites. We first deal with the microstructure of the composite. We distinguish an initial virtual state of the microstructure assuming that the reinforcing yarns show a non-deformed cross-section and that their path depends only on the motion of the bobbins carriers on the braiding plate. A final “realistic” state of the microstructure is determined by taking into account the yarns interactions and the consolidation process assuming a known thickness of the composite. Based on the microstructure geometry, mosaic-type models are developed assuming that the textile microstructure can be mapped into a 3D grid of homogenized elements models. Reuss, Voigt bounds and a last model based on Aboudi’s method of cells are used in order to evaluate the effect of the process parameters on stiffness and strength terms.

The external bonding of fibre reinforced polymers (FRPs) to concrete beams is a particularly attractive rehabilitation technique for increasing or restoring the strength of existing reinforced concrete flexural members. The durability and the performance of FRP-strengthened structures subjected to cyclic loading depend directly on the fatigue behaviour of the FRP itself, as well as on that of the FRP-to-concrete interface. This paper aims at increasing the database on the fatigue behaviour of these types of reinforcement using two test set-ups developed in two distinct research laboratories. The primary purpose of this paper is to propose a methodology for the determination of the value of the allowable shear bond strength (fadh,v,u) and the tensile FRP strength (ff,u) as a function of the numbers of cycles of loading. Results from an experimental investigation on the cyclic behaviour of single-lap and double-lap CFRP-concrete joints are reported. For both types of test set-up, the cyclic bond stress-slip relations are presented and discussed. Analytical S-N relations (cyclic stress range vs. the number of cycles to failure) are proposed.

We aim at studying carbon-epoxy cylinders made by resin transfer moulding by association of braided three-dimensional (3D) tubular preforms with DGEBA-IPD resin. Our study focuses on evaluating energy absorption and mechanical behaviour of 3D braided composite rings laterally crushed between flat platens. Firstly, in an experimental part, we observe their static behaviour. Then, regarding the theoretical part, we obtain absorbed energy in the linear elastic state from analytical stress–strain relations. Energy absorption during non-linear response is approached thanks to an integration of a modelled phenomenological load–displacement relation.

In this paper, four-point bending tests are conducted on Reinforced Concrete (RC) beams with flexural and shear deficiencies. Beams are repaired with externally bonded composite sheets. A full-field optical method, called the grid method, is utilized for measuring displacement fields over predefined areas of interest. The paper firstly describes the basic principle of the grid method. An effort is done for defining accurately the measurement resolution and the spatial resolution. Then, the grid method is applied onto RC beams repaired with Carbon-Fibre-Reinforced-Plastic (CFRP) sheets in flexure. A measurement of crack widths all along the crack length is achieved. Subsequently, crack bridging by the bonded CFRP sheet is characterized. Another example is given for a repair in shear. The grid method is utilized for measuring strain fields over a Glass-Fibre-Reinforced-Plastic sheet which is bonded onto cracked concrete. Strain concentrations are detected at the location of cracks. Moreover, the evolution of strain fields with increasing loads leads to an interpretation of failure mechanism. Finally, both examples prove the great potentiality of the grid method for a sharp characterization of structures containing cracks. The results obtained for shear and flexural strengthening with composites, are original.

This paper deals with the mechanical behaviour analysis for textile reinforced soft composites used for tensile structures. It concerns more particularly the crack propagation strength of polyester fabrics coated with PVC. First of all, we observed and analysed failure mechanisms of a ripped sample, in particular by the evaluation of the influence of the crack length and direction on its propagation under mono-axial tests. Then, as a complement to this first approach, we conducted bi-axial tensile tests on previously notched samples, varying the initial crack orientation and the loading ratios. At last, the application of extensions to the linear elastic fracture mechanics allowed the experimental determination of a parameter specific to crack propagation: the toughness in mode I, KIc.

It is technologically possible to strengthen steel reinforced concrete structures by bonding externally carbon epoxy sheets. Few results exist on the mechanical behavior of strengthened structures subjected to service loads. Consequently, large safety factors are taken into account, most of all concerning the limitation of steel stresses. In order to provide a more accurate characterization of their serviceability, beams are investigated by utilizing a full-field optical measurement technique. The results lead to an original analysis of cracks growth and opening in unstrengthened and strengthened beams.

It is technologically possible to strengthen steel reinforced structures by applying external bonded carbon epoxy composite. The durability and the performance of those reinforcements directly depend on the rheological behavior of concrete-composite interface. From tensile shear thermostimulated tests performed on the interface, we propose a methodology to evaluate the allowable shear stress of the interface by taking into account the effects of time and temperature.

This paper discusses the stiffness and failure behaviour modelling of textile-reinforced composites (TRCs). Different numerical and semianalytical approaches, based on a multilevel geometrical meshing which allows considering mechanical phenomena encountered at the filament, the yarn and the unit cell levels, are developed. The cases of a 2D woven and a 3D braided composites are studied and their homogenised stiffness properties are compared to solutions provided by finite element methods and the fabric geometry model. The modelled failure of both the 2D and 3D TRC are compared to experimental data.

An experimental investigation was conducted to study both the crushing behavior and the practical adhesion of multi-material structures under dynamic compression conditions. Multi-material structures were made by wrapping a carbon/epoxy composite around the outside of an aluminium alloy circular tube. Prior to bonding, different surface treatments (i.e. chemicals etching, anodizing and degreasing) were used in order to improve the practical adhesion between the composite and the aluminium tube. Two geometries of aluminium alloy tubes, allowing a stable crushing mode, were tested. The specific energy absorption values obtained suggest that the influence of surface treatments of multi-material structures was not a significant contribution. For the thinner aluminium alloy tube, with or without the fiber reinforced plastic composites, a diamond mode is observed irrespective of the surface treatments. On the contrary, from a concertina mode obtained with the thicker aluminium tube without reinforcement, a diamond mode is observed with the reinforced one irrespective of the surface treatments. As the crushing mode has changed, the reinforcement applied onto the aluminium tube has decreased the capacities of the structures tested to absorb the energy. On the other hand, the reinforcement applied onto the thinner aluminium tube increased the specific energy absorption of a tube. To get a better understanding of the shock, a high-speed camera was used. It permits to differentiate the ability of a tube to dissipate the energy (i.e. characterized by the specific energy) and the ability of a tube to deform itself (i.e. characterized by the crush distance).

This paper deals with the effective conductivity tensor modelling of textile-reinforced composites (TRC). These TRC are treated as anisotropic heterogeneous media made of regular elements on which we apply a multilevel analysis that allows considering the filament-matrix mixture, the yarn and finally the unit cell scales. Moreover, the determination of the unit-cell effective thermal properties (global properties) takes into account the non-linear thermal behaviour of the constituents (local properties). In a last part, the modellings of unidirectional, 2D and 3D composites are compared to FEM solutions and experimental results in order to validate our approach.

Composite materials find applications in civil engineering for concrete and prestressed concrete structures. The bending design of these structures can be done with a non-linear calculation method. The research presented aims at determining the long-term behavior of a composite repair. The creep of a composite reinforcement/adhesive-layer interface is evaluated by a tensile/shear thermal/stimulation test and a long-term test. Analysis of the results prove that is possible to study, in a comparative way, changes in adhesive mechanical characteristic loss and the viscoelasticity response of different polymer systems. Long-term mechanical characteristics are evaluated and safety coefficients for design are there by deduced.

In the first part of this paper, we have developed a mixed numerical and experimental method for the evaluation of the in-plane stiffness matrix of coated fabrics used in tensile architecture and submitted to biaxial loading. The evaluation of the stress distribution on cross-shaped samples is conducted with a finite element analysis soft ware. In the second part, we have observed and analysed failure mechanisms of previously ripped samples, particularly by the evaluation of the influence of the crack length and direction on its propagation with uniaxial and biaxial tests.

The objective of this work is to study the crushing behavior and the influence of surface treatments on an aluminium alloy before bonding with a carbon/epoxy composite. Two geometries of aluminium circular tubes are used, allowing a stable crushing mode. Chemical etching and degreasing were applied to the aluminium tube to improve adhesion between composite and aluminium. To compare the effects of these surface treatments, the as-received aluminium alloy is used. Under dynamic compression conditions, results have shown that the influence of surface treatments of multi-material structures was not significant in terms of specific energy absorption. Under quasi-static compression conditions, results have shown a 30% increase in specific energy absorption, if we compare the chemically etched tube with the as-received one. For the thinner aluminium tube, if we compare the aluminium tube without reinforcement and the aluminium tube with reinforcement, the same crushing mode has been observed whatever the surface treatment. By contrast, for the thicker aluminium, a crushing mode change was observed. Since the crushing mode changed, the reinforcement applied to the aluminium tube has decreased the capacities of structures tested to absorb energy. On the other hand, reinforcement applied to the thinner aluminium tube increased the specific energy absorption of the tube. To differentiate the ability of a tube to dissipate energy (i.e. characterized by the specific energy) and the ability of a tube to deform itself (i.e. characterized by the crush distance), a new coefficient, termed Abb, was defined to qualify an energy absorber as the ratio of the kinetic energy of the measuring bar after the crushing to the initial kinetic energy.

Residual stress, Young's modulus and practical adhesion of different thickness organic layers made of DGEBA epoxy resin and IPD hardener were determined. Coatings were deposited on aluminum alloy (5754) after degreasing and chemical etching. Both bi-layer (having a perfect interface with a null thickness) and three-layer models (having a real interphase between the organic coating and the substrate) were considered to evaluate residual stress and Young's modulus of the entire coating, the polymer/metal interphase and the remaining part of the coating which have the bulk properties. Coatings, interphase and bulk properties (Tg, reaction extent and interphase thickness) were determined by using differential thermal analysis (DSC) and FTNIR spectroscopy. Young's modulus, curvature radii of coated samples and practical adhesion were determined by three point flexure test. Results show the bi-layer model limitation when a coating/substrate interphase is formed. Interphase thicknesses of 200 and 250 μm were obtained for respectively degreasing and chemical etching. For the same coating formulation and the same curing conditions, amine conversion, Tg of the entire coatings, residual stresses at interfaces interphase/metal and bulk coating/interphase, Young's modulus and practical adhesion depend on the nature of the substrate treatment and on the coating thickness. For thick coatings mechanical, physical and chemical properties are equal to the bulk one. For thin coatings significant differences compared to the bulk properties were observed. Variations of both residual stress and Young's modulus were observed according to different surface treatments. Residual stress intensities at the interphase/substrate interface are higher than the ones at the coating/substrate interface. For thin coatings on chemically etched substrate, Young's modulus is more important than degreased substrate one. On the contrary, residual stress intensities are lower for chemical etching than the degreasing ones. When adhesional failure was observed, the adherence increases when internal stresses at the interface between the metal and the formed interphase decrease.

A computer-aided design tool and a numerical procedure allowing prediction of the behavior of textile-reinforced composites are presented in this paper. Specifying a geometrical description, the software can be used for both simple and complex textile structures. It also aims to provide a basis for subsequent mechanical analysis. Fabric unit cells are regarded as three-dimensional aggregates of subcells to which we apply a multi-scale energetical approach. First, elements to validate the elastic prediction are provided by results obtained on a woven fabric material. The progressive failure procedure is validated by comparisons between simulation and experiments on 3D braided composites.

This paper presents numerical and experimental stiffness characterisation methods for soft composite textile membranes used in fabric roof structures.

In this article, we present a study of the parameters which affect energy absorption in composite structures under dynamic loading conditions and a description of an experimental direct-impact device for the study of such structures. To reduce the field of our investigations, we have limited ourselves to the study of cylindrical tubular structures. The different results show a variation of the specific energy of the composite tubes according to the nature of the fibres, the matrix, the stacking sequence and the loading speed. The strain rate, ge, is a parameter on which various studies have been published and for which conclusions are sometimes still opposed. To satisfy mechanical strengthening and weight problems, multimaterial metal-composite structures have been developed. The results obtained show that, during dynamic tests, some structures exhibit crushing processes leading to significant increases in the specific energies.

Amongst numerous families of composite materials, soft composites associating thermo-plastic matrix with textile reinforcement are used particularly in civil engineering and building construction in the shape of tensile membranes. To give an answer to the permanent use of these structures, it is necessary to know stiffness and failure behavior of those materials, and also to apprehend their long term behavior under combined prompting. So we must develop experimental char acterization technics and rheological models taking into account the specificities of these materials and their long term behaviors.

International audience; Interfacial debonding in multilayered engineering structures can jeopardize the structural integrity without timely awareness. By reconstructing the distribution of interfacial forces and canvassing local perturbance to the structural dynamic equilibrium, an identification approach for interfacial debonding between different structural components was developed. A "debonding index," governed by the derivatives of reconstructed interfacial forces, was established, able to predict debonding in a quantitative manner including the coexistence of multi-debonding and their individual locations and sizes. The index offers the flexibility of detecting debonding between a beam-like component and its neighboring constituents of any type (beam, plate, shell, or even more complex components) with distinct material properties. To enhance the robustness of the approach under noisy measurement conditions, two denoising techniques (low-pass wavenumber filtering and adjustment of measurement density), together with a data fusion algorithm, were proposed. Using a noncontact laser vibrometry, the approach was validated experimentally by identifying multiple debonding zones in a steel-reinforced concrete slab dismantled from a bridge model. The approach has been demonstrated sensitive to debonding of small dimension owing to the use of high-order differential equation of motion. In addition, it does not require a global model of the entire system, prior information on structural boundaries, benchmark, baseline signals, and additional excitation sources as long as the structure undergoes steady vibration.

The objective of the present paper is the optimization of the behavior of structural elements for civil engineering applications. A specific manufacturing process has been developed (Lamtextress patent) allowing to produce hollow beams made of mineral based pultruded composite plates. The beams are hollow with square cross section; they are realized by bonding together composite plates having the dimensions 200 × 10 × 1 cm3. In order to improve the overall performances of the beams, they are reinforced by braiding technology and hand lay-up wrapping. The shear and flexural performance of the final composite beams can be calculated taking into account different process parameters (e.g. nature of fibers, number of filaments, braiding angle).

The development of Textile Reinforced Concrete (TRC) requires the development of design methods. As cement based composites present anisotropic behavior at different levels, we suggest to consider the initial elastic stage of the elementary layer behavior law in tension, compression and shear, limited by a crack opening threshold. Then, we apply the polar method, allowing to optimize a multilayer stacking sequence in order to obtain an overall quasi-isotropic behavior of a composite plate.

This study aims to analyze the textile reinforced concrete tensile (TRC) behaviour. Firstly A tensile test suitable for this type of cracking material is designed and validated. The second phase aims to highlights the influence of several parameters considered as critical (the material, the thickness of the composite, the impregnation of the fibres, the fibre volume ratio) in the textile reinforced concrete (TRC) behaviour in terms of mechanical performance (strength and stiffness) or the amount of damage correlated with the crack opening measured using image correlation analysis.

External bonding of fiber reinforced polymers (FRP) on concrete beams is particularly attractive for the strengthening of civil engineering structures in order to increase their mechanical resistance. The composite material is generally bonded on the tensile part of the beam. In order to design these bonded reinforcements, an iterative computational method based on section equilibrium and material properties (concrete, steel, adhesive and composite) has been developed: this method can be extended to describe the fatigue behavior of RC beams. This paper focuses on the damage behavior of concrete structures subjected to fatigue loading. A specific modeling coupled with an experimental investigation on large-scale beams made it possible to compare the theoretical and experimental fatigue behaviors of RC beams with and without composite reinforcements Results showed that the beam deflection and the strain in each material could be calculated with a sufficient accuracy, so that the fatigue behavior of the FRP strengthened beams was correctly estimated by the model.

This paper concerns the strengthening of concrete structures with externally bonded composite reinforcement, and focuses mainly on the influence of the FRP characteristics on the mechanical behavior of the composite to concrete interface. An experimental investigation was conducted, based on the characterization of such bonded assemblies and using a double lap joint shear test. Twelve different series of specimens were studied in order to evaluate the influence of various parameters related to the FRP material (i.e. the use of carbon or aramid and of fiber reinforced systems, the type of manufacturing process, the values of the Young modulus, the thickness of the FRP and the bonded length) as well as several parameters related to the adhesive joint (i.e. the lap joint thickness, the curing conditions and the elastic modulus of the epoxy adhesive). Analyses of the strain and shear stress distributions along the lap joints emphasized significant effects of the FRP properties and epoxy curing conditions on the interfacial strength. In addition, a bond strength model is proposed in the last part of the study.

Publié suite au congrès : Journées nationales des composites JNC13 AMAC, Strasbourg, 12-14 mars 2003; International audience; The effects of externally bonded composite plates on the mechanical behaviour of a cracked RC beam loaded in flexure are modelled by a multi-scale approach. The problem of crack width prediction is addressed. Firstly, the state-of-the-art methods for crack width prediction in concrete beams are recalled. Then, they are confronted to experimental data obtained with a full-field optical method. It is shown that classical models are not suited for the prediction of crack widths in repaired beams. In order to improve the modelling, a new approach is considered: the structural behaviour of the beam is assessed from numerical computations conducted over a relevant representative volume element. The contribution of this multi-scale approach is that input parameters have a physical meaning and that the results are consistent with full-field measurements conducted on repaired beams. Finally, the paper focuses mainly on the validation of the model for computing displacement fields, crack widths and curvatures in repaired beams. The benefit for the identification of bonding properties between the composite sheet and concrete is also pointed out.

This paper deals with rehabilitation of Reinforced-Concrete infrastructures with externally bonded carbon-epoxy sheets. The flexural behaviour of repaired structures under service loads is addressed, focussing mainly on the problem of crack width prediction. Firstly, the state-of-the-art methods for crack width prediction in concrete beams are recalled. Then, they are confronted to experimental data obtained with a full-field optical method onto small scale beams. Those experiments conducted on physical models show that classical formulae are not suited for the prediction of crack widths in the repaired beams, because they do not take into account the crack bridging effect due to bonding between the composite sheet and concrete. In order to elaborate a numerical modelling, a multi-scale approach is suggested. It is based upon the definition of a relevant Representative Volume Element of beam. The assets are that input parameters have a physical meaning and that the simulated mechanical behaviour is consistent with the one characterized experimentally. Finally, the main results obtained in this study are verified in beams whose scale is representative of real infrastructures. The paper focuses mainly on the validation of the numerical model for computing crack widths in the repaired beams. The interest for the identification of bonding properties between the composite sheet and concrete is also pointed out.