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This article is aimed at proposing a new development of a layer-wise 2D finite-element method for multilayers considering the laminated plate as a superposition of Reissner plates coupled by interfacial stresses. Here, despite the 2D description of the laminates, the interfaces show a particular behavior, elastic or elastoplastic (Von-Mises criterion). The finite element formulation is derived and an eight-node multiparticle element is detailed. The application example of a double lap joint with an elastoplastic adhesive is then considered. The adhesive layer is modeled as an interface. The loading scheme is a load-unload-load one. Interface shear and normal stresses are compared to 3D finite element results. A good agreement between both techniques is observed, particularly for the prediction of the history of the slip between the two adherends and the plastic strains in the adhesive.

Externally bonded composite reinforcements are being used for several decades to repair and upgrade ageing infrastructures. However, the durability of such strengthening systems under service conditions still remains a crucial issue. In this study, an experimental approach based on accelerated ageing tests (at 40°C and 95% relative humidity) is proposed to investigate the durability of the adhesive bond between composite reinforcements and concrete. Two strengthening systems were considered, i.e, carbon fiber sheets and pultruded carbon plates, both associated to bicomponent epoxy adhesives. Property evolutions of both the individual materials (concrete, epoxy adhesives, composites) and the bonded interfaces were monitored over a period of 18 months by means of conventional mechanical tests. Additional DSC characterizations (differential scanning calorimetry) were also performed on the ambient temperature curing adhesives, in order to quantify microstructural changes induced by hydrothermal ageing. Typical ageing mechanisms of the epoxy materials were pointed out and their influence on the mechanical properties of the adhesive joint was discussed.

This article introduces an analytical procedure based on the well-known Shear Lag theory of Volkersen [Die nietkraftverteilung in zugbeanspruchten mit konstanten laschenquerschritten, Luftfahrtforschung 1938;15:41–7], but allowing to take into account a multilinear mechanical behaviour of the adhesive in order to determine an average shear stress profile along the bonded joint. The aim is to provide for a civil engineering application a simple design tool of bonded anchorages. Using this method, more consistent results are obtained concerning the anchorage length and a failure criteria can be expressed in terms of a maximum yielded length along the bonded joint. The validity of this criteria is assessed via an experimental investigation which includes material characterization as well as double lap joints quasi-static loading. The studied materials are a two-component commercial epoxy adhesive and glass fibre pultruded adherends. Different parameters of the joint are varied (surface preparation, adherend and bond thickness, lap length, geometrical configuration) so that it is possible to check qualitative expectations, and define a quantitative failure prediction parameter. In the last part, the shear stress profiles obtained using the described analytical procedure are compared to finite element results and good agreement is found between both approaches.

sous presse; International audience; Structural adhesive bonding is coming into increasing use in civil engineering either for strengthening operations involving the adhesive bonding of external reinforcements or to replace traditional assembly techniques in new structures. However adhesive bonding induces stress concentrations at the edges of the joint, which have been studied by a large number of researchers in order to reduce these phenomena and increase the capacity and service life of the assembly. These studies are all, therefore, concerned with optimizing shear stress transfer in adhesively bonded joints. This paper investigates the role of the hydrostatic pressure on the ultimate capacities of common civil engineering adhesives. This led us to investigate a new joint geometry, the ‘‘curved” bonded joint that naturally creates compressive stresses on the edge of the joint. Initially, classical modelling is conducted to determine how the geometry affects the stresses in the joint. Then, fracture mechanics is used to investigate crack propagation. After this theoretical modelling, several experimental investigations are presented. These are quasi-static tests which compare classical shear lap joints to curved joints. The experimental results are then exploited using the modelling described before. Additional testing is currently in progress, but the curved bonded joint seems to hold good prospects and a patent has been filed.

International audience; Adhesively bonded composite reinforcements are increasingly being used for civil engineering structures. For an adequate use of such a technique, a better knowledge is needed regarding the stress transfer mechanisms involved in polymer joints. This article introduces a single lap shear test for the characterization of the composite-to-concrete or composite-to-steel bonded assemblies. In the first part, an extensive description of the test set-up is given and various methods are proposed to analyse the experimental results. According to Chen's classification (2005) [1], the test under consideration is a near-end supported single-shear test. A first series of tests is reported, that investigates the differences between reinforcement processes based on either pultruded laminates or impregnated carbon fabrics (wet lay-up method), both used for the strengthening of civil infrastructures. The following part discusses the influence of the distance between the extremity of the concrete specimen and the free edge of the adhesive layer. Finally, differences between bonding on concrete and bonding on steel substrates are investigated in a last part. These experimental investigations have allowed us to build-up a considerable body of experience on such usual composite reinforcements, and a large database on this experimental setup and its interpretation

Maintenance sur ouvrages d'art, méthodes d'essais sur structures composites.

L'essai de cisaillement sur joint collé à simple recouvrement est l'un des essais utilisés pour la caractérisation des interfaces collées entre matériaux composites et béton. Cette caractérisation permet de déterminer des paramètres utiles pour le dimensionnement lors d'opérations de réparation ou de renforcement de structures en béton par matériaux composites collés. Cet article décrit dans un premier temps la procédure d'essai associée et s'intéresse de près aux incertitudes de l'essai. Une étude expérimentale est ensuite présentée pour illustrer la méthode d'essai. Cette étude porte sur la réduction de la taille des échantillons utilisés. On remarquera que les dispersions obtenues sont faibles. L'essai présenté a depuis été utilisé pour de nombreux autres types de procédés et les résultats obtenus ont permis de démontrer l'adéquation et la robustesse décrite en terme de dispersion.

International audience; In this paper, a model of laminated plates called M4-5N and validated in a previous paper is modified in order to take into account interlaminar plasticity by means of displacement discontinuities at the interfaces. These discontinuities are calculated by adapting a 3D plasticity model. In order to compute the model, a Newton–Raphson-like method is employed. In this method, two sub-problems are considered: one is linear and the other is non-linear. In the linear problem the non-linear equations of the model are linearized and the calculations are performed by making use of a finite element software. By iterating the resolution of each sub-problem, one obtains after convergence the solution of the global problem. The model is then applied to the problem of a double lap, adhesively bonded joint subjected to a tensile load. The adhesive layer is modeled by an elastic–plastic interface. The results of the M4-5N model are compared with those of a commercial finite element software. A good agreement between the two computation techniques is obtained and validates the non-linear calculations proposed in this paper. Finally, the numerical tool and a delamination criterion are applied to predict delamination onset in composite laminates.

Building and bridge columns are particularly vulnerable when earthquakes occur. Retrofit of deficient reinforced concrete columns with CFRP jackets and bonded CFRP plates is an efficient method to increase their strength and ductility and then to enhance their seismic resistance. However, issues related to anchorage of the plates can be a concern when strengthening flexural concrete members. This study presents specific end-anchors reinforcement systems which were designed and tested under monotonic and low cycle fatigue loading and compared with a reference system commercially available. A total of 16 specimens were tested up to failure, to check the performances of these anchors. It appears that anchors increase the ultimate capacity and ductility of bonded plates.

Nowadays, externally bonded composites are currently used for reinforced concrete structures repair or reinforcement. Such a technique allows increasing the service life of concrete bridges. In the case of steel bridges, applications of this technique are not significant. This may be due to the similarity of both materials rigidity, but also to the lack of confidence of structure owners in using structural adhesive bonding as assembly technique. In the scope of a research work led by the IFSTTAR (Institut Français des Sciences et Technologies des Transports, de l’Aménagement et des Réseaux) interested in the repair of steel structures, we have investigated composite to steel bonded assemblies. This article presents some of the realized investigations. It first introduces the field of use of the technique and its advantages. Then, characterization of stress transfer through adhesive bonding is presented, and some accelerated ageing and pseudo-fatigue tests are described. Though more work is needed on the topic, obtained results allows considering the technique as suitable for steel structures.

7th International Conference on FRP Composites in Civil Engineering (CICE), VANCOUVER, CANADA, 20-/08/2014 - 22/08/2014; In order to join a plane composite cable to the main structure of a composite footbridge designed within (Caron, 2009), it was decided to investigate structural adhesive bonding. This technique is indeed particularly adapted to composite materials. However structural adhesive bonding induces stress concentrations at the edges of the adhesive joint, which have been studied by a large number of researchers in order to reduce these phenomena and increase the capacity and service life of the bonded joint (Kinloch, 1987). These studies are all concerned with optimizing shear stress transfer in adhesively bonded joints. This paper investigates the role of hydrostatic pressure on the ultimate capacities of common civil engineering adhesives. The conclusions led us to study a new joint geometry, the 'curved' bonded joint that naturally creates compressive stresses on the edge of the bonded joint. Several experimental investigations are presented within this paper to illustrate the optimization. These are quasi-static tests that compare classical shear lap joints to curved joints. Additional testing is currently in progress, but the curved bonded joint seems to hold good prospects and a patent has been filed.

40th IABSE Symposium Tomorrow's Megastructures, NANTES, FRANCE, 19-/09/2018 - 21/09/2018; This paper presents some results obtained in the Infravation research project called 'Fast and effective solution for steel bridges life-time extension' (FASSTbridge). The aim of this project is to develop and demonstrate a reliable, preventive, cost-effective and sustainable solution for steel bridges fatigue life-time extension. As a demonstration example, the Jarama Bridge was selected in this project. The Jarama bridge is located in the outskirts of the city of Madrid, over the river Jarama on road M-111, and has a total length of 115,5m and 5 spans (max span length 33,5m).Erected in the 1960s, it has suffered since then a considerable increase of traffic flow which was not considered at its design stage. This paper leads a cost-benefit analysis and a life cycle analysis of the CFRP solution compared with traditional techniques (use of steel plates) and considering the economic and environmental profit of the preventing policy. The aim is to adopt a preventive strategy to allow road administrations enlarging the service life of steel and composite steel bridges in a cost-effective and sustainable manner.

During its life-time, a bonded assembly is subjected to various ageing mechanisms which may induce synergistic effects. In the case of civil structures strengthened by bonded fiber reinforced polymer (FRP), the influence of coupled mechanical/environmental factors is still a matter of investigation. In this context, an innovative experimental device has been designed to study the durability of concrete/FRP interfaces subjected to both sustained load and hydrothermal ageing. This test setup is able to load simultaneously several double shear specimens and can then be installed in a climatic chamber in order to superimpose accelerated ageing conditions to the creep load. Besides, the design of the test-bodies is compatible with an existing single shear method that allows to determine the residual capacity of aged specimens. This paper aims at describing the proposed creep test setup and its instrumentation, as well as the validation stages, including a comparison of preliminary experimental data with simple analytical and finite element modeling approaches.

After corrosion, fatigue phenomenon is the main cause of damage in old metallic structures. Fatigue cracks appear in stress concentration area subject to high stresses, and can lead to the ruin of the bridge. In old metallic structures, fatigue cracks mainly occur at the edge of the rivet hole and are thus difficult to detect with the common non-destructive inspection technique (NDI). Moreover, due to the poor quality of the old metallic materials, particularly puddled iron, some of the NDI techniques cannot be used. The main objective of the present work is to study the effectiveness of carbon fibre reinforced polymer (CFRP) laminates in reinforcing fatigue crack emanating from the rivet hole. Thus, investigations on small-scale specimens were done. These specimens consist of metallic plates with center hole from which one single crack emanates. Two metallic materials, puddled iron and mild steel, and two reinforcement processes were used. These reinforcement processes consist of Normal Modulus (NM) and Ultra High Modulus (HHM) CFRP laminates. Furthermore, symmetrical and un- symmetrical reinforcement configurations are considered as well as pre-stressing NM laminates before application. The experimental results showed firstly the efficiency of the different studied reinforcement configurations in slowing down crack propagation. In conclusion of this work, the achieved results, particularly those in terms of Stress Intensity Factor, could be used for reinforcement of riveted structures by CFRP bonding, taking into account the presence of rivets as well as the presence of the others elements of the assembly.; La fatigue représente la deuxième cause d'endommagement des structures métalliques anciennes après la corrosion. Celle-ci se manifeste par l'apparition de fissures, dans les zones fortement sollicitées présentant des concentrations de contraintes importantes, et peut mener à terme à la ruine de l'ouvrage. Dans le cas des structures métalliques anciennes, les fissures de fatigue s'amorcent généralement au droit des trous de rivets rendant difficile leur détection par les techniques de contrôle non destructif conventionnelles. De même, les matériaux métalliques anciens de la construction, et notamment le fer puddlé, limitent l'utilisation de certaines techniques. Dans le cadre de ce travail de thèse, l'objectif principal est d'étudier l'efficacité d'un renforcement par composites collés dans le cas de fissures de fatigue émanant de trous de rivets. Pour cela, des éprouvettes de petites dimensions, présentant un perçage central et une unique fissure de fatigue en bord de perçage, ont été considérées. De même, deux matériaux métalliques, acier doux et fer puddlé, ainsi que deux procédés de renforcement PRFC (polymères renforcés de fibres de carbone), à Module Normal et à Ultra Haut Module, sont étudiés. Pour chaque procédé de renforcement, différentes configurations de renforcement ont été testées et notamment la mise en précontrainte du plat composite MN avant collage. Cela a permis de mettre en évidence l'efficacité de la technique de collage de plats PRFC pour un renforcement à la fatigue de matériaux métalliques anciens. Par ailleurs, les expressions analytiques simples proposées pour le facteur d'intensité de contraintes pourront par la suite être utilisés pour une application aux structures rivetées en tenant compte de la présence du rivet ainsi que celle des plaques assemblées.

After corrosion, fatigue phenomenon is the main cause of damage in old metallic structures. Fatigue cracks appear in stress concentration area subject to high stresses, and can lead to the ruin of the bridge. In old metallic structures, fatigue cracks mainly occur at the edge of the rivet hole and are thus difficult to detect with the common non-destructive inspection technique (NDI). Moreover, due to the poor quality of the old metallic materials, particularly puddled iron, some of the NDI techniques cannot be used. The main objective of the present work is to study the effectiveness of carbon fibre reinforced polymer (CFRP) laminates in reinforcing fatigue crack emanating from the rivet hole. Thus, investigations on small-scale specimens were done. These specimens consist of metallic plates with center hole from which one single crack emanates. Two metallic materials, puddled iron and mild steel, and two reinforcement processes were used. These reinforcement processes consist of Normal Modulus (NM) and Ultra High Modulus (HHM) CFRP laminates. Furthermore, symmetrical and un- symmetrical reinforcement configurations are considered as well as pre-stressing NM laminates before application. The experimental results showed firstly the efficiency of the different studied reinforcement configurations in slowing down crack propagation. In conclusion of this work, the achieved results, particularly those in terms of Stress Intensity Factor, could be used for reinforcement of riveted structures by CFRP bonding, taking into account the presence of rivets as well as the presence of the others elements of the assembly., La fatigue représente la deuxième cause d'endommagement des structures métalliques anciennes après la corrosion. Celle-ci se manifeste par l'apparition de fissures, dans les zones fortement sollicitées présentant des concentrations de contraintes importantes, et peut mener à terme à la ruine de l'ouvrage. Dans le cas des structures métalliques anciennes, les fissures de fatigue s'amorcent généralement au droit des trous de rivets rendant difficile leur détection par les techniques de contrôle non destructif conventionnelles. De même, les matériaux métalliques anciens de la construction, et notamment le fer puddlé, limitent l'utilisation de certaines techniques. Dans le cadre de ce travail de thèse, l'objectif principal est d'étudier l'efficacité d'un renforcement par composites collés dans le cas de fissures de fatigue émanant de trous de rivets. Pour cela, des éprouvettes de petites dimensions, présentant un perçage central et une unique fissure de fatigue en bord de perçage, ont été considérées. De même, deux matériaux métalliques, acier doux et fer puddlé, ainsi que deux procédés de renforcement PRFC (polymères renforcés de fibres de carbone), à Module Normal et à Ultra Haut Module, sont étudiés. Pour chaque procédé de renforcement, différentes configurations de renforcement ont été testées et notamment la mise en précontrainte du plat composite MN avant collage. Cela a permis de mettre en évidence l'efficacité de la technique de collage de plats PRFC pour un renforcement à la fatigue de matériaux métalliques anciens. Par ailleurs, les expressions analytiques simples proposées pour le facteur d'intensité de contraintes pourront par la suite être utilisés pour une application aux structures rivetées en tenant compte de la présence du rivet ainsi que celle des plaques assemblées.