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In the framework of sustainable development policies, it is essential that infrastructure owners can rely on effective repair or strengthening solutions, designed and tested in relevance to actual service conditions. In the case of steel structures, fatigue damage is a major concern that can significantly affect the lifespan of the structure, and so far, there are very few operational methods capable of preventing fatigue cracks in the field. Adhesively bonded carbon fiber reinforced polymer (CFRP) composites are being successfully applied to the rehabilitation of concrete structures for more than two decades, and they are currently receiving much interest for the strengthening of steel elements, but mainly for curative purpose after severe damage has occurred. In the present study, which is part of a European project called FASSTbridge, a specific CFRP system has been developed as a preventive method against fatigue damage of steel structures. The proposed system consists of a commercially available ultra-high modulus (UHM) CFRP composite plate compatible with the stiffness of the host steel structures, which is bonded to the steel support using a novel hybrid epoxy/polyurethane adhesive. A first part of the paper presents the main specifications that should be adopted in the design of CFRP strengthening systems applied to steel structures, and that were identified from an extensive literature survey. These specifications have guided the development of the polymer adhesive and the choice of a peculiar commercial CFRP plate in the preliminary phase of the project. Experimental characterizations were then conducted (i) on the formulated hybrid polymer adhesive to optimize its curing schedule and check the previous specifications are fulfilled, and (ii) on CFRP reinforced steel specimens in order to verify the effectiveness of the proposed strengthening system. This experimental program involved both short term and durability tests that were performed by different laboratories. Such an inter-laboratory study made it possible to verify the performances of the developed strengthening system and to assess the influence of installation parameters and environmental conditions. The authors wish to acknowledge Epsilon Composite Company for supporting the study. This work is part of the FASSTBRIDGE project. This project has received funding from the European Union’s Seventh Framework Programme for research, technological development and demonstration under grant agreement no 31109806.0008. FASSTbridge is co-funded by Funding Partners of The ERA-NET Plus Infravation and the European Commission. The Funding Partners of the Infravation 2014 Call are: MINISTERIE VAN INFRASTRUCTUUR EN MILIEU, RIJKSWATERSTAAT, BUNDESMINISTERIUM FÜR VERKEHR, BAU UND STADTENTWICKLUNG, DANISH ROAD DIRECTORATE, STATENS VEGVESEN VEGDIREKTORATET, TRAFIKVERKET – TRV, VEGAGERÐIN, MINISTERE DE L'ECOLOGIE, DU DEVELOPPEMENT DURABLE ET DE L'ENERGIE, CENTRO PARA EL DESARROLLO TECNOLOGICO INDUSTRIAL, ANAS S.p.A., NETIVEI, ISRAEL - NATIONAL TRANSPORT INFRASTRUCTURE COMPANY LTD, FEDERAL HIGHWAY ADMINISTRATION USDOT

One of the aims of applying sustainable development to bridge infrastructure was to provide bridge owners with strengthening solutions that could lead to increased service life for existing structures. In the case of steel bridges, the assessment of the remaining service life is most often linked to the determination of structural deterioration caused by corrosion and fatigue. Damage caused by fatigue is very difficult to assess before crack initiation and is more likely to occur in older structures, where the phenomenon was not taken into account in designs before 1970. In addition, old steel materials display more brittle behavior. To meet these challenges, a preventive methodology for fatigue strengthening of steel structures was developed. The method begins with scheduling a fatigue design analysis of the existing construction to determine the most fatigue damage exposed construction elements of the bridge. The remaining fatigue life of these elements can be increased with a strengthening solution based on the use of adhesively bonded ultra-high modulus (UHM) carbon fiber-reinforced polymer (CFRP) plates, which were applied to a steel surface before failure indicators such as cracks arise. This article presents the development process of this preventive method and a demonstrative application to an existing bridge (Jarama Bridge). Strain measurement was carried out to verify the theoretical expectations of the reinforcement. Different parameters were studied, including the influence of low traffic volumes during the reinforcement application. The results proved the efficiency of this system for the structure under study.

Nowadays, welding in steel structure design is the most widely used assembly technology. In the case of bridge structures, it has replaced riveting and bolting for the past thirty years. It is well known that this type of structure may deteriorate not just because of corrosion but also because of fatigue issues. In the case of corrosion, specific maintenance actions are currently being undertaken by bridge owners to increase the life span of their structures, such as painting operations. In the case of fatigue issues, it is well known that the high level of residual stresses due to the welding process may increase fatigue hazards. Several techniques may be used to reduce the high level of tensile stresses in the top layer of the weld near the welding toe. In this paper, the influence of welding and shot-peening parameters is investigated. A 3D finite element model is proposed and improved. The model results are compared to the residual stresses measured on several samples using X-ray diffraction method. Effects of the shot diameter, speed and angle impact are investigated. The transverse and longitudinal residual stresses near the welded joint, with a peak tensile stress value of 250 MPa and 280 MPa respectively, drop to a compressive stress value of more than 50 MPa and fit with the experimental results.

In the case of exceptional accidents, nuclear containment structures may be submitted to an internal temperature increase. This may have an influence on the prestressed concrete structures behavior regarding both its mechanical performance and its porosity. The presented study got interested on the impact that a temperature increase may have on the mechanical behavior of the steel reinforcement for both prestressing strands and rebars. In order to remain in realistic situations, it was chosen to study temperatures between 20°C and 140°C. Some experimental investigations regarding the tensile behaviour of steel rebars and their adherence within concrete will first be presented. Then, some investigations on steel strands will be described: some tensile tests at different temperatures, and some relaxation tests to check how the level of prestress loss may be affected by the temperature. This experimental study is part of a national French project (MACENA) aiming at assessing the impact of an accident on the behavior of nuclear containment structures. The gathered experimental data will be used for their damage assessment.

This study focuses on the modeling of the local bond behavior of Fiber Reinforced Polymer (FRP) reinforcing bars and the surrounding concrete. An analytical bond-slip model is first proposed to describe the interface behavior of the bars embedded in concrete. Then, the parameters of the bond-slip law are identified from experimental data of pull-out tests performed on specimens instrumented with optical fiber sensors. A specific procedure was developed to identify the model parameters. In a second step, the identified analytical law is introduced in a finite element model (cohesive zone damage model) to simulate the pull-out tests, and a complementary model calibration is proposed to account for the non-uniform stress distribution along the interface. Finally, calculated strain profiles at the bar/concrete interface are compared with the experimental profiles measured by optical fiber sensors. The proposed model is found suitable to simulate the bond mechanisms at high load levels, when there is significant interface damage. However, further development of the model is needed to accurately describe the bond stress and slip response at lower load levels and low/moderate interface damage.

International audience; Fastening or reinforcement onto an existing steel structure may create constraints such as the use of hot works (i.e. welding) or loss of weathertightness (i.e. drilling holes and bolting). In order to limit these constraints, there may be a strong interest in using adhesively bonded fasteners. Such a solution requires however strong justification especially regarding long-term properties. This paper presents the results of experimental and numerical investigations realized on the creep behaviour of such bonded fasteners developed for offshore steel structures. Experimental investigations were conducted at room temperature following a precise and repeatable implementation protocol. The results of the various investigations revealed a non-linear evolution of creep displacements according to a Burger law. Numerical modelling has therefore been developed on the basis of Burger's law. A preliminary static study aimed at validating the geometric model and analyzing the initial stress state in the adhesive. The creep study was then carried out to compare numerical results to experimental ones. Although additional investigations are needed, numerically determined creep displacements demonstrated a good consistency with the experimental investigations.

One of the goals of sustainable development applied to bridge infrastructure is to provide bridge owners with strengthening solutions that may lead to an increase of existing structures service life. In the case of steel bridges, the assessment of the remaining service life is most often linked to the determination of the structural deterioration caused by corrosion and fatigue. Damage caused by fatigue is very difficult to assess before crack initiation, and is more bound to occur in old structures, for which the phenomenon was not taken into account in design before 1970. In addition, old steel materials present a more brittle behavior. In answer to these challenges, the FASSTbridge project, financed through European Infravation call, aimed at developing a pre- cracking fatigue assessment and strengthening methodology for steel bridges based on the technology of adhesively bonded composite. The proposed article presents some of the results of this project.

International audience; This paper presents a model of prestressing steel relaxation under various levels of loading and temperature. This incremental model enables the delayed strain of prestressing steel wires to be calculated and takes the non-linear coupling of temperature and loading effects into account. It considers different experimental results that could occur in nuclear containment structures, for which a temperature up to 140 °C could be reached for prestressing wires should a loss-of-coolant accident occur. The constitutive law for prestressing steel relaxation is presented, followed by an illustration of the numerical implementation of the proposed model. Finally, the model responses are confronted with experimental results available in the literature supplied by Toumi Ajimi et al. (2017) for the thermo-mechanical conditions between 20 and 140 °C in terms of temperature and 70%–80% of loading ratio.

SMAR 2017, the fourth International Conference on Smart Monitoring, Assessment and Rehabilitation of Civil Structures, ZURICH, SUISSE, 13-/09/2017 - 15/09/2017; The use of adhesively bonded composite reinforcement is relatively widely used for concrete structures. Yet, some questions remain regarding its use in the case of prestressed concrete structures especially in relation with the influence of existing cracking and the verification of the encountered damage phenomena at real scale. French National Organism Cerema with the help of French motorway bridge owners association ASFA and French National Research Organism IFSTTAR realized several real size experimental investigations of an old prestressed concrete beam coming from a deconstructed bridge to answer these questions (Project CLERVAL). Both flexure and shear tests up to failure were carried out and several measurement methods were used to understand the role of the composite reinforcement on the behavior of the structure and the damage scenario. Acoustic emission was one of these methods and two different systems were investigated. The proposed communication will first describe the two used acoustic systems and their dedication. A specific development will then be presented aiming at optimizing the obtained acoustic phenomena localization. Finally, main results will then be presented for both flexure and shear tests. The obtained results are currently compiled with the results from the other measurement methods. This should allow to better understand the damage process of reinforced prestressed concrete beams and to assess the precision of existing reinforcement design methods.

International audience; Bonded composite constructions using timber and ultra-high performance fibre reinforced concrete (UHPFRC) are investigated as highly innovative structural elements technically and economically efficient, and having better environmental performances. Such technique could indeed offer new structures typologies for bridges for instance associating timber for main beams with UHPFRC slabs. In timber-concrete- composite structures, connection is traditionally achieved with mechanical means. The research presented herein describes the timber-concrete assembly by adhesive bonding and specially the behaviour of bonded joint between Laminated Wood (LW) and UHPFRC. This type of assembly has to be investigated concerning mainly the durability of the bonded assembly and its ability to transmit the forces concentrated on edges. The present study describes the development of a test called ''Push-Out'' used to characterize the behaviour of the timber-concrete bonded after or prior to environmental ageing. Following the development of the used test protocol, investigations are realized on four different commercial resins to study the influence of the adhesive stiffness on the force transfer focusing in particular on the failure mode, on the ultimate capacities and some local deformations. The mechanical behaviour of the bonded joint is investigated in particular from a theoretical point of view and from the determination of deformation field obtained by Digital Image Correlation (DIC).

The assessment of the structural resistance of historical metal structures involves a depth understanding of many factors, such as the properties of the constructions materials and the structural behaviour of the connection mode. Available information regarding the behaviour of historical riveted connections is quite limited and more information about the residual strain and stress state is still needed in order to allow the preservation of these existing structures. This paper deals with the assessment of stress and strain field which exist around the rivet hole due to the hot riveting process. Experimental specimens were manufactured with riveting technique used in aged metal bridges and different metallic materials for the joined plates were considered. Strain and thermal measurements were done during and after the overall riveting process. The results of the experimental investigation allowed the assessment of the residual strain state and the thermal response of the riveted joint. The experimental results were then used for validation of a 2D axisymmetric model. On the basis of the results obtained, the pre-stress state can be evaluated as well as the stress concentration areas where fatigue cracks may initiate. Thus, the provide findings constitute a supportive tool for further studies regarding the assessment and rehabilitation of historical riveted structures.

MCD2016, 8th Rilem International Conference on Mechanisms of Cracking and Debonding in Pavements, Nantes, FRANCE, 07-/06/2016 - 09/06/2016; Old steel bridges made in mild steel or wrought iron were assembled by riveting, an assembly technique which is no longer used today. This one induces stress concentration, residual stresses creation and leads to fatigue prone details in such bridges. Cracking that propagates from a rivet hole, hidden by rivet head, is the typical phenomenon of fatigue damage of riveted members. Thus, especially because of increase traffic, fatigue is among the major issues for old steel highway and railway bridges (over 100 years old). Moreover, these structures are often considered as historical ones and modifications of the original element must be limited. For all these reasons, CFRP composites seem to be a good solution that could lead to fatigue life increase. Fibre-reinforced polymer (FRP) has been widely used to strengthen concrete structures and has a great potential to strengthen steel structures. However, limited amount of research has been done on the application of these materials to old steel materials. This paper deals with the study of cracked steel elements and their reinforcement by adhesively bonded carbon fiber-reinforced polymer (CFRP) under fatigue loading. Studied specimens have typical dimensions encountered in old steelriveted joints. A real crack is propagated at the edge of the hole under fatigue loading and composites materials are then bonded taking into consideration the size of the rivet head. Several different CFRP systems were tested and their efficiency compared. Test results, theoretical and modeling considerations of the different studied configurations are presented in this paper

L’essai de cisaillement sur joint collé est l’un des tests mécaniques utilisés pour la caractérisation des interfaces collées entre matériaux composites et supports en béton. Ce type d’essai permet de déterminer des paramètres utiles au dimensionnement des systèmes composites collés utilisés pour le renforcement et la réparation des ouvrages d’art. Cet article décrit dans un premier temps la procédure d’essai associée et s’intéresse à la dispersion des résultats. Une étude expérimentale traite ensuite de l’influence de la nature du support sur le transfert des efforts par cisaillement, puis de l’optimisation de la taille des échantillons utilisés. Depuis sa mise en service, le dispositif présenté a permis de caractériser de nombreux systèmes de renforcement composites et a démontré sa robustesse et sa fiabilité en termes de dispersion des résultats. Il a en outre fait l’objet d’une méthode d’essai des Laboratoires des Ponts et Chaussées.

This paper investigates the creep behavior of adhesively bonded concrete/fiber-reinforced polymer (FRP) joints, through experimental and modeling approaches. The first part proposes a methodology for predicting the long-term creep response of the bulk epoxy adhesive; such a procedure consists of (1) performing short-term tensile creep experiments at various temperatures and stress levels, (2) building the creep compliance master curves according to the time–temperature superposition principle in order to assess the long-term evolution for each stress level, and (3) developing a rheological model whose parameters are identified by fitting the previous master curves. In our case, it was found that master curves (and, consequently, parameters of the rheological model) are dependent on the applied stress level, highlighting the nonlinear creep behavior of the bulk epoxy adhesive. Therefore, evolution laws of the model parameters were established to account for this stress dependence. The second part focuses o...

fig., bibliogr.; International audience; The aim of this paper is the enhancement and validation of a layerwise model applied to the analysis of laminates with thin layers of an elastic-plastic adhesive. The thin adhesive layers are modeled as imperfect interfaces across which displacement discontinuities exist. In a previous paper, the constitutive equations of the imperfect interfaces were empirically established without following the layerwise logic. The model equations are revisited and a solid theoretical justification of the new enhanced equations is obtained by making use of the Hellinger-Reissner functional. A theoretical validation of the model is performed by comparing its predictions to those of a solid finite element resolution in the case of a T-peel joint. The results of the enhanced version of the model are very accurate whereas those of the previous version are erratic for the considered joint. As compared to the solid finite element method, an important saving in computational cost is achieved.

This study investigates the use of an elasto-plastic adhesive in a bonded double lap joint to increase its ultimate capacity. The first section describes the experimental work we performed to characterize the materials and measure the shear strain along the joint. A comparison between an elastic adhesive and a highly plastic adhesive is made and the effect of the type of behaviour on both the capacity and the characteristic anchorage length is studied. The second section then compares the experimental results with a classical 3D finite element model. Good correlation was found between numerical expectations and experimental measurements, and the modelling allowed us to highlight typical phenomena linked to the use of an elasto-plastic adhesive. In addition, a parameter based on a microscopic measurement has been defined which allows us to describe the onset of plasticity and predict maximum capacity.

International audience; The Navier laboratory has worked from many years on the development of composite timberconcrete structures to obtain new typologies of structures, technically and economically efficient, and having better environmental performance using structural adhesive bonding to ensure a almost-perfect connection between the two materials However, many doubts still exist concerning its possible use for this type of application concerning mainly the durability of the bonded assembly and its ability to transmit the forces concentrated on edges. The present study describes the development of a test called "Push-Out" used to characterize the behaviour of the timber-concrete bonded assembly. Following the development of used test protocol, investigations are realized on three different commercial resins to study the influence of the adhesive stiffness on the force transfer focusing in particular on the failure mode, on the ultimate capacities and some local deformations. These various investigations conducted in parallel should finally allow choosing the most suitable adhesive for the intended use.

fig., bibliogr.; International audience; In this paper, the layerwise model for laminates with imperfect interfaces and enhanced in Part 1 of this work is confronted with experimental results. The model calculations are validated by comparing its sliding predictions in double lap adhesive joints to the sliding measurements performed in a previous paper. The model predictions agree with the experimental results. Finally, the model is applied to the failure analysis in double lap joints and T-peel joints exhibiting adherend, adhesive and cohesive failures. The model calculations and pertinent failure criteria provide accurate predictions and may become a helpful tool suitable to the design of adhesive joints.

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

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.

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.