Influence du revêtement sur le comportement en fatigue des dalles orthotropes (étude d'une solution en BFUP)

Les tabliers métalliques à dalle orthotrope sont sensibles au phénomène de fatigue produit par les charges des poids lourds du trafic. Ce comportement n'est pas précisément prédit avec les méthodes de l'Eurocode 3, compte tenu de la complexité des effets locaux et de la connaissance insuffisante du rôle mécanique du revêtement (diffusion des charges et participation à la flexion locale). De plus l'augmentation du trafic des camions et éventuellement celle des charges admissibles par essieu en Europe tend à rendre ce problème bien plus critique. Le renforcement de ces tabliers est donc souhaitable de façon à prolonger la durée de vie des ponts existants, et aussi augmenter la durabilité des nouveaux ponts. Le béton fibré à ultra hautes performances (BFUP) a été envisagé comme nouvelle solution de revêtement, étant donné ses propriétés mécaniques, ses possibilités de mise en œuvre et sa durabilité. L'objectif de cette thèse, réalisée dans le cadre du projet ANR Orthoplus, est de quantifier expérimentalement l'apport des revêtements couramment utilisés dans les structures à dalle orthotrope et de valider la solution innovante en BFUP. Des essais statiques et dynamiques sur corps d'épreuve à grande échelle (2,40x4,00) m2 ont été réalisés sur la plate-forme d'essai des structures de l'IFSTTAR. Quatre corps d'épreuve ont été testés : tôle de platelage de 14 mm non revêtue et revêtue de 80 mm de béton bitumineux, tôle de 10 mm revêtue de 35 mm de BFUP et tôle de 12 mm revêtue de 35 mm de BFUP. L'influence des différents types de chargement positionnés au centre des corps d'épreuve a été analysée : plaques métalliques type Eurocode 1 et vraies roues de camion. L'étude a porté sur le détail de fatigue: liaison auget-tôle de platelage entre pièces de pont. La contrainte géométrique de fatigue (extrapolation au point chaud) a été évaluée expérimentalement en utilisant deux schémas d'extrapolation linéaire des déformations à proximité du cordon de soudure du détail étudié, le schéma du rapport CECA et celui proposé par l'Institut International de Soudure, à partir des mesures réalisées au-dessous de la tôle de platelage ( T) et sur l'âme de l'auget ( A).La cohérence entre estimation quasi-statique des déformations et comportement sous cycles de fatigue a été vérifiée, ainsi que la rigidification importante apportée par le BFUP, bien que ce dernier ne participe pas avec une connexion totale. Les résultats expérimentaux ont été confrontés à des modèles de différents niveaux de complexité qu'il reste nécessaire de calibrer empiriquement pour prévoir les contraintes géométriques. A partir des contraintes de fatigue obtenues expérimentalement, nous avons calculé la durée de vie des dalles orthotropes testés à l'aide de la règle du cumul linéaire de l'endommagement. Enfin nous avons mené une étude par analyse de cycle de vie d'un pont à dalle orthotrope pour vérifier la pertinence environnementale des différentes solutions de revêtement. Les nombreuses données expérimentales acquises dans ce travail sont de nature à permettre une amélioration significative du dimensionnement rationnel des tabliers à dalle orthotrope et de leur revêtement pour une meilleure prise en compte de leur gestion durableOrthotropic steel bridge decks are sensitive to fatigue damage induced by live heavy traffic loads. This behaviour is not precisely predicted by Eurocode 3, because of the complexity of local effects. The pavement overlay is not taken into account for calculating the fatigue resistance because of the lack of knowledge concerning its mechanical behaviour (loads diffusion and participation in the local deflection) and the behaviour of the composite structure. Moreover, the increase in heavy traffic and potential regulations evolution in Europe towards an increase of acceptable loads of truck axles - tend to render the orthotropic decks fatigue behaviour an even more critical issue. The reinforcement of these steel decks is therefore crucial to extend the service life of existing bridges, and also increase the durability of new bridges. Ultra-high performance fibre-reinforced concrete (UHPFRC) has been chosen as a possible alternative topping layer considering its remarkable durability, flowability and mechanical properties. The purpose of this thesis, carried out within the framework of a joint R&D project called Orthoplus, is to quantify experimentally the mechanical contribution of topping layers currently used in orthotropic steel bridge decks and validate an alternative concept using UHPFRC coating. Static and dynamic tests of large scale panels (2,40x4,00) m2 were carried out at the IFSTTAR Structures Laboratory. Four prototypes have been tested: a 14 mm thick deck plate without surfacing, the same deck plate associated with 80 mm of bituminous concrete surfacing, a 10 mm thick deck plate topped with 35 mm of UHPFRC and a panel with the same UHPFRC topping layer and a 12 mm thick deck plate. The influence of different centered load types and configurations has been analyzed: rectangular steel plates according to Eurocode 1 and real truck wheels. The experimental programme has been focused on the rib-to-deck welded joints at mid-span between two transverse crossbeams. The fatigue geometrical stresses in the deck and the trough, respectively denoted as D and T, have been derived from two linear extrapolations of measured strains next to the toe of the welded joint: the extrapolation schemes from the ECSC report and from the IIW document. Consistency between quasi static strains and deflections estimate and behaviour under fatigue cycles has been verified, as well as the significant additional stiffness provided by the UHPFRC overlay, although its contribution does not correspond to a perfectly connected composite section. The experimental results have been compared to simple and more complex models which still need empirical calibration for predicting the geometrical stresses. Using the experimentally obtained fatigue geometrical stresses the service life of the tested prototypes were calculated using Miner's rule. Finally a life cycle assessment study of an orthotropic steel bridge deck was carried out to verify the environmental relevance of the alternative topping layer solutions. The numerous experimental data obtained from this work shall make it possible to significantly improve the rational design method of orthotropic slabs and their associated deck overlay, in view of a better accounting of their long term and sustainable structural managementPARIS-EST-Université (770839901) / SudocSudocFranceF

Modélisation du couplage chimico-mécanique pour calculer une structure en béton atteinte de réaction sulfatique interne

La réaction sulfatique interne (RSI) correspond à la formation tardive d'ettringite qui provoque un gonflement du béton, incompatible avec la rigidité du matériau et sa faible capacité en extension, ce qui engendre des fissurations dans la structure. Dans cet article on présente une modélisation chimico-mécanique, formulée à l'échelle macroscopique, qui permet de prédire le comportement du béton dégradé par la RSI. Ce modèle est basé sur une approche thermodynamique décrivant la formation de l'ettringite à l'intérieur d'un milieu poreux. Il tient compte de l'histoire thermique du béton au jeune âge et des conditions environnementales (température et humidité)

Structural elements made with highly flowable UHPFRC: Correlating computational fluid dynamics (CFD) predictions and non-destructive survey of fiber dispersion with failure modes

Structural design with highly flowable Fibre Reinforced Concrete has to duly take into account the preferential alignment of fibers, which can be governed through the rheological properties of the fluid mixture and the casting process and by the geometry of the structure. The possibility of predicting the fiber alignment, by tailoring the casting process, and of non-destructively monitoring it, can foster more efficient structural applications and design approaches. Focusing on UHPFRC slabs with pre-arranged casting defects, the flow-induced alignment of the fibers has been predicted by means of a suitable CFD modelling approach and hence monitored via a non-destructive method based on magnetic inductance properties of the fiber reinforced composite. The comparison between the assessed data on the fiber orientation and the crack patterns as visualized by image analysis supports the effectiveness of casting flow modelling and non-destructive fiber dispersion monitoring in supporting the structural design of elements made with highly flowable fiber reinforced cementitious composites

Résistance au choc des structures en béton : du comportement du matériau au calcul des ouvrages

Cette thèse a fait l'objet, dans sa version définitive éditée, d'une publication dans un format relié aux éditions du LCPC (1995-hors collection). Ouvrage disponible sur demande adressée au LCPC, service IST.The present thesis may be considered as a first step to control the shock strength of concrete structures. It has contributed to developping the knowledge about the material dynamic behaviour in order to improve the design of structures against accidental loadings. In a first part the physical mechanisms that were pointed out by direct tensile tests, at gradual strain rates from the quasi-static regime up to the domain of hard shocks (Hopkinson Bars technique) are listed. Several expressions of the strength evolution versus the strain rate are proposed, accounting for the influence of characteristic material parameters. An optimization of the concrete mix-design regarding high rate loadings has been considered. In a second part the shock tube test of concrete slabs is described. This testing process was developped in order to validate at the level of an ideal structure the results that had been obtained at the material level. Data recorded on 24 slabs constituted of different reinforced or unreinforced concretes are presented in details. Analyzing such data allows checking different approximated design methods, and defining the absolute requirements of more sophisticated dynamic computational modellings, that are still to be processed.Cette thèse s'inscrit comme une étape vers la maîtrise de la résistance au choc des structures en béton, en développant la connaissance du comportement dynamique du matériau pour mieux calculer les ouvrages vis-à-vis des chargements accidentels. Une première partie récapitule les mécanismes physiques mis en évidence grâce aux essais de traction directe à des vitesses échelonnées du régime quasi-statique au domaine atteint lors des chocs durs (technique des barres d'Hopkinson), et propose plusieurs expressions de l'évolution de la résistance avec la vitesse, en fonction des paramètres caractéristiques du matériau. On a pu en déduire une optimisation du béton par rapport aux sollicitations dynamiques rapides. Une deuxième partie décrit l'essai de dalles au tube à choc, mis au point pour valider sur une structure modèle les résultats obtenus à l'échelle du matériau. Les données recueillies sur 24 dalles constituées de différents bétons, armés ou non, sont présentées en détails. Leur analyse permet de tester plusieurs méthodes de calcul approchées, et de définir un cahier des charges incontournable pour des modèles de calcul en dynamique plus sophistiqués, qui restent à développer

UHPFRC - Mechanisms and applications

Symposium le futur du ciment : 200 ans après Louis Vicat, PARIS , FRANCE, 06-/06/2017 - 08/06/2017Ultra-high Performance Fibre-Reinforced Concrete (UHPFRC) has emerged around 25 years ago as a fruitful result of dedicated research efforts based on the combination of three main ideas : Strength and compactness improvement of cement materials by intense reduction of the water to binder ratio, which was made more and more possible and efficient with R&D advances in superplasticizers and mineral additions ; Use of fibers to provide post-cracking tensile capacity and pseudo-ductility, which was made possible thanks to more than two decades of conceptual and exploratory development of conventional fiber-reinforced concrete, and reallyefficient as compared to it due to the high quality of the matrix and the possiblity to incorporate high amounts of fibers ; Reduction of natural imperfections due to aggregate in limiting their size and selecting very high quality materials in anoptimized grading, which took benefit of aggregate packing models having being developed in the late 80s. This combination enabled to produce several industrially controlled patented materials markedly overpassing the highest high-performance concrete available at this time, with 150 MPa-characteristic compressive strength at least, and possibly dispensing with the traditional use of secondary reinforcement due to material non-brittleness and with thick cover in aggressive environment. This allowed dispensing with keeping systematic continuity with traditional reinforced concretedesign provisions. Moreover, mixing, placement, thermal treatment and formwork technology could be kept understood in the continuity with emerging self-compacting concrete. Twenty years ago, the first major applications, Sherbrooke footbridge (Canada) and prestressed beams for the renovation of the heat exchange zone in the cooling towers of Cattenom power plant (France), demonstrated outstanding strength and resistance to transfer, so that durability and lightness of prestressed members have appeared as main advantages to be searched in structural applications. The first recommendations for production, characterization of UHPFRC and structuraldesign using these materials, published in France in 2002 [1], made it possible to explore the implementation possibilities of such materials especially for pre-stressed structures and non-reinforced thin elements. Application to bridges and footbridges (Bourg-lès-Valence in 2001, Sakata Mirai and Seoul - Seon Yu Footbridges in 2002, Pinel bridge in 2006, passerelle des Anges in 2008) motivated consistent research efforts to ensure controlled quality of the material produced and placed, and safe design provisions of lighter and thinner structures. Optimized shapes, like ITE® beams, ribbed slabs or shells, were demonstrated as favourable for valuable implementation, while cost-efficiency also relied on indirect material savings or lightness benefits for the method of execution. Besides valuable application in structural components, UHPFRC has been adopted for a decade by architects to develop attractive façade and roofing components, thanks to new aesthetic possibilities associated to durable mineral surface quality, lightness and possible complex shapes and semi-transparency, with typical examples of Villa Navarra roof and 'Les enfants du Paradis' net panels in 2007. For such elements, the use of organic or stainless steel fibres was developed, the range ofmixes was extended addressing the fire-resistance demand and the possibly lower strength requirements, and ribbed plates or shells with passive reinforcement in the stiffeners tended to appear as structurally efficient. Growing interest andeconomic significance of this development in building applications turned out evident from the first international symposium strictly dedicated to UHPFRC applications, organized in Marseille (France) in 2009 [2]. From the same time however, UHPFRC produced volume took off also for less visible, however technically optimized projects of the extension of Haneda Airport in Tokyo, light prestressed bridges in Malaysia, or joint fills between precast beams in North American projects of 'accelerated bridge (re)construction'. The year 2013, associated to the second UHPFRC international symposium organized in Marseille [3] and revised edition of AFGC Recommendations, has constituted a significant milestone for UHPFRC in France. Two major projects associated to urban renovation, the MuCEM in Marseille (Fig. 1) and the Jean Bouin Stadium in Paris, had been completed, having led to widened awareness of technical and architectural capabilities of these 'new concretes' both among professional (architects and engineers) and for the public, including clients of constructions. Technical acceptance of the design, industrial processes and details associated to these projects, as well as previous satisfactory French 15 years-experience of building componentsand bridges made of UHPFRC, has made it possible to launch the standardization process in France. This has resulted in the elaboration of three complementary standards, related to UHPFRC structural design, material production and control, and execution of structures. The first two documents have been published in French and English in 2016 [4-5], the latter one is expected for 2017, as well as updating of the standard 'common rules' for precast concrete products. Although based onthe technical consensus expressed in AFGC recommendations revised in 2013, the standards elaboration has promoted clarification and simplification of the ordering / qualification processes for easier UHPFRC contract implementation. Since 2013, international recognition especially within ACI Excellence in Concrete Construction Awards program has been gained not only for the MuCEM and Jean Bouin Stadium in 2015, but also for the 'Ring of Memory' at International Memorial of Notre-Dame de Lorette in 2016. Noticeably enough, due to optimization in conceptual design, UHPFRC has made possible competitive solutions not only for tailor-made projects, but also for typical bridge situations exemplified by the Buthaumont Bridge and the footbridge at Le Cannet des Maures. In Switzerland with the iconic example of Chillon viaducts, in the US with the Pulaski viaduct restoration, and progressively also in France, bridge deck repair or protection using UHPFRC has deserved increasing interest. Repair solutions, for buildings also, are increasingly considering UHPFRC due to specific versatility, structural and durability performance and weight savings, which results in cost-efficiency despitea possibly still high unitary material cost. However, the driving field of UHPFRC application in France has concernedcladding and roofing panels, for buildings (e.g. 'Vente PriÎe' Headquarters, 'La Mantilla' buildings...) and for largeinfrastructure projects (e.g. Montpellier high speed railway station). UHPFRC solutions based on ultra-thin, highlytransparent and architecturally appealing elements have thus been made possible in a cost-efficient way due to the lightnessof these secondary elements.Consolidation of engineering and industrial know-how is a key condition for further development of such applications. Thishas been the case among several architects, designers, checkers, engineering offices, and precasting plants, although quitefew. Education associated to the standards dissemination should strengthen these capabilities. Further research anddevelopment efforts should address advanced UHPFRC modelling, seismic design with UHPFRC, development of typical'UHPFRC solutions', and non-conventional process optimization (sprayed UHPFRC, 3D printing etc.) which could widenthe scope of cost-efficient UHPFRC implementation

Contribution à l'identification et la prise en compte du comportement en traction des BFUP à l'échelle de la structure

Les Bétons Fibrés à Ultra hautes Performances (BFUP) se caractérisent par une résistance en compression bien supérieure à celle des BTHP couverts par la normalisation, une excellente durabilité et l'emploi d'un assez fort taux de fibres métalliques modifiant le recours habituel aux armatures. Ils sont notamment marqués par une résistance à la traction élevée. Cependant, selon le pourcentage volumique et le(s) type(s) de fibres initialement prévus dans la formulation et l orientation réelle des fibres dans la structure vis-à-vis des directions principales de traction, leur comportement en traction peut être adoucissant ou écrouissant. Ces deux comportements nécessitent une approche différente pour assurer la sécurité du dimensionnement. Dans un premier temps, des méthodes de caractérisation du comportement en traction des BFUP ont été mises au point de manière à déterminer quel comportement va se mettre en place pour un BFUP et un élément structurel donné, en s appuyant sur l essai de flexion quatre points réalisé sur éprouvette non-entaillée. Cet essai nécessite l utilisation d une analyse inverse afin d obtenir la loi de comportement contrainte-déformation (dans le cas d un BFUP écrouissant en traction directe) ou contrainte-ouverture de fissure (dans le cas d un BFUP adoucissant en traction directe). La configuration de l essai de flexion quatre points pouvant entraîner des artefacts, elle nécessite un raccordement avec l essai de traction directe. Pour valider ce raccordement, une méthode d essai permettant de tester des corps d épreuve de dimensions identiques en flexion et en traction directe a été mise au point. Les résultats de l analyse inverse des essais de flexion ont été comparés à ceux des essais de traction directe. La comparaison a notamment permis de démontrer la robustesse des méthodes d analyse proposées en particulier vis-à-vis de la cohérence de la discrimination écrouissant/adoucissant à partir du relevé de fissures sur chaque éprouvette. Dans un second temps, des méthodes de calcul adaptées à une approche type contrainte ouverture de fissure ou contrainte déformation ont été testées ou développées afin de prédire la résistance ou le comportement des poutres en BFUP soumises à des sollicitations concomitantes de flexion et d effort tranchant. Cette configuration de sollicitation fait en effet intervenir de façon critique le comportement en traction du matériau. Pour valider ces méthodes de calculs, onze poutres en BFUP armé ou précontraint, avec ou sans armatures transversales et avec ou sans fibres (métalliques ou organiques) ont été testées sous une configuration de flexion conduisant à une rupture par effort tranchant. La caractérisation simultanée du comportement mécanique des BFUP à l échelle du matériau en prenant en compte l orientation réelle des fibres au sein des poutres, qui constitue une originalité de ce programme, s est avérée particulièrement importante pour constater l interaction entre le matériau, la géométrie de la structure et le procédé de mise en œuvre du BFUP sur l orientation des fibres. Les méthodes d analyse des essais de flexion quatre points mises au point ont permis d évaluer quantitativement l influence de la structure sur les paramètres caractérisant le comportement en traction du BFUP, notamment la déformation correspondant à la localisation de la fissure et marquant la fin du comportement global pseudo-plastique . Les conditions de synergie d éventuelles armatures transversales et du BFUP vis-à-vis de la résistance à l effort tranchant, ont pu être mises en évidence. Pour étendre l analyse, la capacité de l approche en contrainte ouverture de fissure à prédire la résistance de poutres soumises à des sollicitations concomitantes de flexion et d effort tranchant a été testée. L approche en contrainte déformation a également été appliquée, contribuant au développement et à la validation de méthodes élastoplastiques adaptées aux BFUPUltra High Performance Fiber Reinforced Concrete (UHPFRC) are characterized by a compressive strength much higher than Very High Performance Concrete (VHPC) currently considered by standardisation, an excellent durability and the use of relatively high content of fibers. In particular, their tensile strength is quite important. Nevertheless, depending on fibers ratio and fibers types forecasted in the initial mix design and the real orientation of fibers in the structure compared with the main tensile directions, UHPFRC can exhibit either strain-softening or strain-hardening tensile behaviour. Each considered behaviour needs specific approaches in order to ensure a safe design. In a first time, characterization methods of UHPFRC tensile behaviour have been developed in order to determine which type of behaviour will occur considering a given UHPFRC and structure. These methods are based on the four point bending test. An inverse analysis of the results of this experimental method permits to deduce the stress strain relationship (in the case of hardening UHPFRC) or stress crack opening relationship (in the case of softening UHPFRC). The results depend on assumptions assumed during the inverse analysis. Thus, we have developed analysis methods which minimize the number of hypothesis in order to predict the most realistic behaviour law. The four point bending test configuration can involve artefacts. A comparison with direct tensile test is then necessary. In order to conduct this comparison, a direct tensile test method has been developed. It permits to use specimens with the same cross-section for direct traction and for the four point bending configuration. The results obtained from four point bending tests associated with the inverse analysis have been compared to those obtained with direct tensile tests. This comparison has been achieved using results of an experimental campaign considering different specimens sizes and two UHPFRC. Such comparison allows to highlight the effectiveness of the proposed method and particularly, its capability to deduce a strain-hardening or strain-softening behaviour of the material from observed crack patterns. In a second time, calculation methods adapted for stress crack opening or stress strain approaches have been tested or developed in order to predict the ultimate capacity or behaviour of UHPFRC beams submitted to a coupled shear and bending loading. Indeed, for this loading configuration, the tensile behaviour of the material is a main parameter. In order to validate the proposed calculation methods, eleven beams made of reinforced or prestressed UHPFRC, with or without stirrups and with or without fibers (metalics organics) have been tested in bending conducting to shear failure. The concomitant characterization of the UHPFRC mechanical behaviour at the material scale , taking into account the real orientation of fibers within the beams, constitutes an originality of this program. It has been useful to analyze the interaction between material, structure configuration and casting method on the orientation of fibers. Moreover, developed analysis methods of four point bending tests have been used to evaluate the influence of the structure (real orientation of fibres, influence of an eventual prestress or the structure configuration) on the parameters characterizing the tensile behaviour of the UHPFRC, in particular the strain corresponding to the localization of a critical crack. The conditions of additional contribution of UHPFRC and eventual stirrups in the shear capacity of the beam have been described. In order to extend the analysis, the approach based on the stress crack opening relationship has been tested in order to predict the shear capacity of beams. The approach based on stress strain relationship has also been applied, participating to the development and the validation of elastoplastic methods adapted to UHPFRCPARIS-EST-Université (770839901) / SudocSudocFranceF