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International audience; The use of structural adhesive bonding is under development for offshore applications and more specifically for fastener connection to existing steel structures. For this application, creep appears to be one of the main long-term phenomena that needs to be considered during the design approach. To investigate this issue, experimental creep investigations were realised at real scale for two bonded fastener geometries at different stress levels and under different load situations (tension and shear). Local measurements were carried out during these investigations to better describe the long-term behaviour of the bonded fasteners. Despite the non-uniform adhesive thickness in the assembly, numerical investigations have highlighted that the stress field mainly depends on the fastener geometry and the applied load level. This article is dedicated to the description of a methodology that relies on a precise inverse identification of creep parameters and on simplifying hypotheses on the stress field to be able to use simple analytical tools. The methodology enables to identify creep parameters much quicker than a method coupling an optimisation algorithm and a finite element analysis and could easily be used for more complex and precise models.

International audience; Similarly to other industrial areas, there is a strong interest for the use of bonded FRP (Fiber Reinforced Polymers) repair or reinforcement for steel structures in the case of offshore applications. However, the reliability of the adhesively bonded (FRP) shall stand as high as steel renewal, this requires additional developments, in particular, a complete understanding of the repair mechanical strength which depends on material and interfacial properties. Fracture mechanics is an interesting approach to assess the risk to undergo interlaminar fracture or steel to adhesive interfacial disbonding failure. The experimental determination of the required design values for this an approach (critical toughness) are generally obtained using common tests such as Double Cantilever Beam (DCB), End Notched Flexure (ENF) or Mixed Mode Bending (MMB) tests. These tests require a precise crack length monitoring that is currently carried out using visual observation or Digital Image Correlation (DIC) on the flank of the sample. This may induce error in crack length measurement especially if the crack doesn't remain straight during the test. The paper presents a study of crack front monitoring by a distributed optical fiber as an alternative to the standard techniques to monitor crack front and to determine the critical toughness in mode I and II through respectively, DCB (Double Cantilever Beam) and ENF (End Notched Flexure) tests. Firstly, the issues related to the use of this continuous optical fiber are raised (insertion, precision resolution, measurement noise, exploitation methodologies). Then, some experimental investigations on ENF and DCB tests are presented and analyzed using the proposed methodology to monitor crack propagation using the optical fiber strain measurement. The obtained results are compared, focusing on the proper determination of the critical toughness of the adhesive. These results show that an optical fiber bonded on the surface of the sample can be used to measure and follow the crack propagation during the test which simplifies and adds precision to the standardize critical toughness computation method.

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.

International audience; With an ageing bridge stock and in order to limit economic and environmental costs, developing preventive maintenance, repair and strengthening strategies will help asset owners to make efficient decisions in a sustainable way. For steel and composite steel bridges, preventing fatigue failure is at stake. In this context, easy-to-apply preventive strengthening techniques should be developed to extend fatigue life-time of steel bridges and delay resource-consuming major interventions such as traditional steel strengthening, rehabilitation, or decommissioning and new construction.This paper investigates the cost and environmental burdens associated with several strategies to extend steel bridges fatigue life-time. In particular, one details the needed information and the methodology for the implementation of an overall life-cycle analysis of an adhesively bonded CFRP solution compared with traditional techniques (use of steel plates). This is carried out considering economic, environmental and social benefits of the preventing policy and illustrating the developed methodologies with a case study corresponding to the strengthening of an existing steel bridge during its service life.

This study focuses on the experimental characterization of the bond behavior between concrete and Fiber Reinforced Polymer (FRP) reinforcing bars (rebars). Pull-out tests were performed on glass, carbon, and aramid FRP rebars, as well as on deformed steel rebars. The influence of various parameters on the bond behavior was studied, such as the type of fibers, the diameter of the FRP bars and their surface geometry. Scanning-Electron-Microscope (SEM) observations were performed to precisely study the sand coating characteristics of these rebars. A main originality of the proposed approach relied on the instrumentation of pull-out samples using Distributed Optical Fiber Sensing (DOFS) instrumentation. Such a distributed measurement system provided access to the longitudinal strain distribution along the rebar near the rebar-concrete interface, and then made it possible to determine the effective development length of the various types of rebars considered in this study. As the introduction of DOFS instrumentation may be intrusive, its influence on the interface behavior was also discussed.

This paper reports an experimental study performed to investigate the effectiveness of carbon fiber reinforced polymer (CFRP) laminates in extending fatigue life of old cracked metallic structures. Specimens consist of old metallic plates, mild steel and wrought iron, with one single crack emanating from a rivet hole. This cracking configuration has never been adopted in literature studies and was chosen to be representative of real cracked elements in riveted connections. Two different initial crack lengths before reinforcement, representing two degrees of fatigue damage, were adopted. Four strengthening configurations were investigated including single-sided and double-sided strengthened specimens, Normal Modulus (NM) CFRP plates with or without pre-stressing, and Ultra High Modulus (UHM) CFRP plates. «Beach marking» technique as well as crack gauge were used to monitor and record the crack propagation during fatigue loading. Experimental results show that the application of CFRP plates can effectively reduce the crack growth rate and extend the fatigue life. CFRP plates with high modulus were found to be more efficient. This study represents a contribution to the present state of research and provides some interesting results on crack propagation in CFRP repaired elements close to real riveted ones.

In civil engineering, structural adhesive bonding is increasingly used for the reinforcement or rehabilitation of degraded structures using adhesively bonded composite materials. However, the presence of defects within the bonded joint may affect the effectiveness of the assembly, and their detection is still an issue. The purpose of our study is to evaluate the acousto-ultrasonic (AU) method to detect and identify most common types of defects encountered in adhesively bonded joint and more specifically in FRP reinforced structures. Two types of assembly (made of carbon fibre reinforced polymer pultruded plates bonded on steel or concrete support) were investigated considering three types of defect (voids, kissing-bond defects simulated using a layer of grease at the composite-adhesive interfaces, and weakly polymerized zones implemented through a softer adhesive). The objective of this work is to investigate the ability of acousto-ultrasonic method to detect all those types of defects in the bonded joint with a data-driven methodology. It is expected that the extracted features from the received signals represent the damage state in the joint. For the methodology, a data-driven modelling by means of a Principal Component analysis is performed. Additionally, a Random Forest (RF) is trained using extracted parameters.

This paper investigates the influence of a low elevated temperature on the mechanical behavior of steel B500B rebars and T15.2 prestressing wires in nuclear containment structures. Tensile tests were carried out to evaluate the evolution of mechanical properties during heating. The bond between concrete and rebars was also studied and relaxation tests on prestressing wires have been done. Between 20 °C and 140 °C, the mechanical behavior of rebars and tendons exhibited no major deteriorations. However, a high decrease of the ultimate bond was observed for pull-out tests. Concerning relaxation tests, the temperature tends to significantly increase the relaxation rate.

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.

CICE 2018, Conférence internationale sur les composites à matrice polymère renforcée de fibres en génie civil, PARIS, FRANCE, 17-/07/2018 - 19/07/2018; A strengthening system with adhesively bonded CFRP reinforcement was developed in the Infravation project FASSTbridge to extend the remaining fatigue lifetime of existing steel bridge constructions. The premature debonding of CFRP and steel is seen as a major risk to lose the contribution of the retrofitting system. Consequently, an ultrathin debonding sensor to be integrated in the adhesive layer between steel and CFRP was developed as part of the strengthening system. It is suited for continuous monitoring of the integrity of the adhesive joint.The paper explains the underlying physical principles of the sensor and gives insight into the performed tests for the calibration and verification of its functionality. The sensor conception takes the change of a capacitor's electrical impedance as a basis, which occurs when a change in distance between the adjacent conductive faces takes place. It is well assumed that debonding yields separation, which leads to an increase of the monitored impedance. The relationship is explored through single lap sheer experiments and vertical tension bond tests. The sensitivity and the accuracy of the impedance with respect to deformations are revealed by comparing several groups of prototypes with different dielectric layers and viscous materials. The influences of different temperature effects and fatigue loadings are also presented.

CICE 2018, Conférence internationale sur les composites à matrice polymère renforcée de fibres en génie civil, PARIS, FRANCE, 17-/07/2018 - 19/07/2018; Steel bridges present frequent fatigue problems that reduce their load-carrying capacity and residual life. The mainstream method to strengthen steel bridges, the attachment of steel plates to the tension flange of the girders, has several disadvantages. Carbon Fiber Reinforced Polymers (CFRP) composites, though more expensive than steel plates (price per unit/m2), have relevant advantages for the retrofitting of steel bridges: their application is less intrusive to the existing structure and less time-consuming than traditional. The overall objective of FASSTbridge is to develop and demonstrate a reliable preventive, cost-effective and sustainable solution for steel bridges life-time extension using CFRP instead of steel plates. This paper will present the developed fatigue assessment tool used to determine the remaining fatigue life of steel structures and will introduce the design of reinforcement in fatigue using adhesively bonded CFRP. Finally, the gain in service life using this methodology will be presented.

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.

CICE 2018, Conférence internationale sur les composites à matrice polymère renforcée de fibres en génie civil , PARIS, FRANCE, 17-/07/2018 - 19/07/2018; Recent studies have shown the efficiency of the application of carbon fiber reinforced polymer (CFRP) materials to reinforce cracked steel elements even in the case of old steel materials (mild steel and puddled iron). Bonding CFRP materials on cracked steel plates leads indeed to a significant reduction of the stress intensity factor (SIF) at the crack tip and thus to a significant increase of the fatigue life. This is even more pronounced when using ultra-high modulus or pre-stressed reinforcement. This could allow extending damaged steel structures service life or securing a structure waiting for a more complete refurbishment. Yet, there is currently a clear lack of design tools for the design office to be able to apply such reinforcement or repair technique.The presented work concerns the appraisal of a methodology based on the use of finite element modelling to determine the stress intensity factor modification ratio. After the presentation of the proposed methodology, it will be compared with experimental investigations led by the authors on different steel substrates and with different reinforcement processes. This comparison will allow to identify the precision of the method, and to be able to highlight its strengths and weaknesses. Finally, parametric analyses will be done to assess the impact of different design characteristics on the increase of fatigue life

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

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.

Offshore structures are submitted to aggressive environmental conditions as it is in salty environment, submitted to important bio-colonization, and higher mechanical fatigue due to cyclic wave loading. Because of these conditions, the maintenance of these structures plays a key role in their reliability over time. The use of monitoring in such a case could allow drastic decrease of maintenance costs provided safe and reliable systems may be applied on site. In this context, IFSTTAR is currently working with several partners in a regional project called SURFFEOL (Survey and reliability of offshore wind turbines jackets) in order to provide to offshore wind farms developers such solutions. One of the main objectives of this project is to carry out health monitoring of a wind turbine steel foundation to determine damage factors in relation more particularly with corrosion and fatigue degradations. The presented work introduces our laboratory investigations concerning different electrochemical and nondestructive techniques used to monitor these damage mechanisms. Firstly, accelerated corrosion tests by artificial tidal cycle with natural seawater are described on carbon steel coupons with and without protective coating in order to monitor the evolution of corrosion versus time. Several parameters are measured during the test such as corrosion intensity, pH, corrosion potential and environmental parameters (temperature, seawater salinity, O2 dissolved). Secondly, fatigue sensors and more classical strain gauges have been used before and during fatigue to monitor damage under normalized fatigue cycles. The tests were carried out on T welded joints until failure. For each case, the comparison of the different techniques allows concluding on their suitability. Further investigations in laboratory are currently done to ensure such a conclusion, especially on durability issue. The final validation of these techniques will then be done on site with the help of a reduced-scale prototype at sea near French Atlantic coast.

International audience; Cerema in France has set up an experimental project about a prestressed concrete bridge beam recovered during the demolition of a bridge. Before testing, an accurate diagnosis of the beam has been achieved. Three series of tests were carried out in 2014: bending tests before reinforcement, after a first phase of reinforcement bonded composite materials, and finally after a second and final phase of reinforcement bonded composite materials. This final test was gradually led to a complete break of the beam. Traditional instrumentations were installed on the beam: 187 measuring points were monitored at a frequency of 10 Hz by twenty five PEGASE WiFi connected sensors. Innovative instrumentations were also used and compared with the traditional ones. This experience on a precast, prestressed concrete bridge beam reinforced with FRP allows us to deliver some first lessons. The real break of the beam was held to a force of about 61 tonnes, corresponding to a bending at mid-span to about 20 cm. Thereafter, the effort has been decreasing. The complete shearing by delamination of the bonded composite reinforcements (which have thus accompanied the beam to maximum effort of loading), was held to a force of about 59 tonnes, corresponding to a bending to about 27 cm. The complete break in bending in a controlled section (cracking up in the upper table) was obtained for an imposed displacement of more than 40 cm.

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

CICE 2016, 8th International Conference on Fibre-Reinforced Polymer (FRP) Composites in Civil Engineering, HONG-KONG, CHINE, 14-/12/2016 - 16/12/2016; 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. The FASSTbridge project, financed through European Infravation call, is aimed at developing a pre-cracking fatigue assessment and strengthening methodology for steel bridges, based on the technology of adhesively bonded composite. The methodology will include an assessment method of remaining fatigue life of existing structures, the design and on-site application of a strengthening system, and the environmental and economical appraisal of the solution. A new strengthening technique based on CFRP plates will be developed. This technique will include the formulation and production of a specific adhesive, specifications for using commercial CFRP plates, and the definition of instrumentation plans to monitor the performance of the strengthening system. Finally an on-site application in an actual steel bridge will be carried out, to verify the quality of the proposed solution.

The shear strength of concrete/rock interface must be clearly assessed to design the rock foundations. However, the concrete/rock interface has different failure modes which depend on the mechanical characteristics of the materials and the morphology of the rock surface. Consequently, to study thoroughly the shear behavior of concrete/rock interface and to define the cracking mechanisms and debonding propagation along the interface, different instrumentation devices were applied during a large scale direct shear test. A large sample formed by pouring concrete over a large rock surface (shear surface of 1.5 m²), was instrumented using the following techniques: strain gauges, acoustic emission and distributed optical fiber sensor. The different observations made during the test were combined to determine the successive stages of interface failure. The strain gauges, which measure local strains within the materials, showed their ability to detect the crack propagation in the materials and the debonding at the interface. The acoustic emission technique was able to detect the damages in the materials and at their interface. The optical fiber sensor measured strains evolution of the concrete near the interface showing the crack propagation during the test and the progressivedebonding at the interface., Pour la conception de fondation au rocher, la résistance au cisaillement de l'interface béton-roche doit être évaluée. Or cette interface présente différents modes de rupture qui dépendent des caractéristiques mécaniques du matériau et de la morphologie de la surface rocheuse. Différentes instrumentations ont donc été mis en place au cours d'essais de cisaillement à grande échelle afin d'étudier le comportement au cisaillement de l'interface béton roche et de déterminer les mécanismes de fissuration et de décohésion à l'interface. Une éprouvette constituée d'une surface rocheuse de 1.5m² sur laquelle du béton a été coulé, a été instrumentée des dispositifs suivants : jauge de contrainte, capteur d'émission acoustique, fibre optique. Les différentes observations effectuées durant les essais ont été utilisées pour établir les étapes successives de rupture de l'interface. Les jauges qui permettent une mesure locale de la déformation, ont démontré leur leur capacité à détecter la propagation de fissure dans les matériaux, roche et béton et la décohésion à l'interface. L'émission acoustique a permis de détecter l'endommagement des matériaux et à leur interface. La fibre optique a permis de mesurer l'évolution des déformations dans le béton à proximité de l'interface, et en particulier la propagation de fissures et la décohésion progressive à l'interface.

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.

In this paper, the durability of the adhesive bond between concrete and carbon fibre reinforced polymers (CFRP) strengthening systems has been investigated under accelerated ageing conditions, i.e. , at 40 °C and 95% relative humidity. Mechanical characterizations were carried-out on control and exposed CFRP strengthened concrete specimens, in order to assess the evolutions of the adhesive bond properties during hydrothermal ageing. Results from different experimental campaigns are presented and reveal significant evolutions (decrease in the adhesive bond strength and/or change in the failure mode) depending on various parameters, such as the surface preparation of concrete, the presence of a carbonated concrete layer, the nature of the CFRP overlay (carbon fibre sheets or pultruded CFRP plates), the ageing behaviour of the bulk epoxy adhesive itself, or the test configuration used to evaluate the adhesive bond strength (pull-off or shear loading test). Moisture diffusion from the superficial layer of concrete ( i.e. , diffusion of interstitial pore solution) towards the adhesive joint is suspected to be a key factor driving the degradation process during hydrothermal ageing.

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.

ICCE International Conference on Composites/Nano-engineering, CHENGDU, CHINE, 12-/07/2015 - 18/07/2015; The use of composite reinforcing bars (rebars) for the reinforcement of concrete appears as an attractive solution to prevent corrosion, which is the main pathology encountered on concrete structures. Although such rebars are being used for more than ten years, there is a clear lack of knowledge regarding their durability, especially under alkaline environment.This paper aims at investigating the evolutions of tensile properties and bond in concrete of GFRP (Glass Fiber Reinforced Polymer) bars under accelerated laboratory environmental conditions. Both plain rebars and rebars embedded in concrete specimens were exposed to these conditions, in order to assess the influence of the alkaline environment. GFRP rebars were chosen for this study, as this type of bars is considered as the most economically competitive solution in comparison with classical steel rebar.

In order that non destructive testing methods become quantitative tools for structure owners, it is needed to assess their precision and sensitivity to the environment. The presented study deals with two electromagnetic methods classically used to survey road pavements and concrete structures: a radar technique and a capacitive technique. The presented investigations aim at assessing the influence of temperature and moisture on the two methods for measurements realized on concrete slabs. The temperature was ranging from 5°C to 45 °C and the surrounding relative humidity (RH) evolved between 60% and 90%. The study is part of a more ambitious topic aiming at defining quantitative non destructive methods to evaluate the water content of concrete structures on site and their state of degradation. The presented work allows assessing the sensitivity of both radar and capacitive techniques to the environmental conditions: temperature and relative humidity. Moreover, the measurement variability of the used capacitive probes with three different sets of electrodes is estimated.

TRA 2014, PARIS, FRANCE, 14-/04/2014 - 17/04/2014; Aramid Fiber Reinforced Polymer (AFRP) rebars are being used as internal reinforcements of concrete structures for more than ten years. Their main advantages over common reinforcing steel rebars rely on their lightness, durability performances, mechanical properties, and electromagnetic neutrality. For this application, interfacial properties between the rebars and surrounding concrete play a major role on the mechanical performances of the reinforced concrete structure. In this context, this research aims at investigating the bond behaviour of commercially available AFRP rebars embedded in concrete. The first part of the paper is devoted to the assessment of mechanical and physical properties of the selected rebars. A second part is then dedicated to the study of interfacial properties between the rebars and concrete: the interfacial bond strength is first assessed using a specifically designed pull-out test, and a modelling of the interface behaviour is then developed, based on an analytic bond-slip law. The method used to identify key theoretical parameters of the model is also discussed.; Les armatures en Polymère Renforcé de Fibres d'Aramide (PRFA) sont utilisées pour le renforcement des structures en béton depuis plus de dix ans. Leurs principaux avantages au regard des armatures traditionnelles en acier réside dans leur légèreté, leur durabilité, leurs propriétés mécaniques, et leur neutralité électromagnétique. Un point clé gouvernant l'efficacité de tels renforcements réside dans leur capacité à adhérer correctement au béton. La présente étude s'intéresse donc à la caractérisation de l'adhérence entre le béton et des armatures en PRFA disponibles sur le marché. La première partie de l'article est consacrée à la présentation des armatures étudiées et à la caractérisation de leurs principales propriétés physiques et mécaniques. La seconde partie de l'étude s'intéresse à la détermination du comportement mécanique à l'interface entre les armatures et le milieu béton. Le comportement de l'interface est tout d'abord évalué à l'aide d'un essai d'arrachement spécialement conçu, puis est analysé au travers d'une modélisation originale. Pour mettre en oeuvre cette dernière, une méthode d'identification des paramètres du modèle est proposée.

International audience

This paper aims to examine the effectiveness of seismic strengthening of reinforced concrete (RC) columns by externally bonded Fibre Reinforced Polymer (FRP). Particularly, a novel strengthening system, designed for the flexural strengthening of columns is studied. This flexural strengthening is achieved by FRP plates bonded longitudinally and anchored at the column-stub junction. The proposed system is validated through an experimental campaign carried out on full-scale RC columns. Different strengthening configurations have been applied on columns, which were tested under combined constant axial and reversed cyclic lateral load. The experimental results demonstrate that bonded FRP enhance the bending moment capacity and flexural deformation capacity of strengthened columns. Those tests helped us to analyze the behaviour of columns depending on the FRP confinement (FRP jacket) and the coupling of the confinement with the anchored flexural strengthening. It was then found that the proposed anchoring system is a promising constructive dis-position for the seismic strengthening of columns, but this system needs to be improved.

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.

CFRP strengthened concrete specimens were submitted to accelerated ageing conditions (40°C and 95% R.H.) and the time evolution of the adhesive bond strength was monitored using either pull-off or shear loading tests. In a parallel investigation, effects of hydrothermal ageing on the microstructure of the bulk epoxy adhesives were assessed by means of thermal analyses and tensile tests. From those experiments, it was found that the property evolution of the concrete/FRP bonded interface is primarily dependent on the sensitivity of the polymer to ageing conditions, but also on the type of test used for the mechanical characterizations. These trends were supported by numerical modeling based on finite element analysis.