Nos sistemas de revestimento de fundo de aterros sanitários e pilhas de rejeito de mineração, é comum utilizar geotêxtil não-tecido para a proteção ao puncionamento da geomembrana por objetos pontiagudos como a brita. Neste trabalho, realiza-se um estudo experimental a fim de avaliar a superfície deformada de geomembrana de PEAD, com 2 mm de espessura, em camada de proteção sujeita a carregamentos de 600 kPa e 1800 kPa ao longo de 100 h, com o objetivo de simular danos mecânico de operação. Para a leitura da superfície deformada da geomembrana utilizou-se um lençol de chumbo localizado sob a geomembrana e as suas deformações foram estimadas a partir de uma máquina de leitura por coordenadas, com grid de 4 mm. Além deste, foi estimada a superfície deformada da geomembrana para o grid de 1 mm, com a aplicação do método de interpolação chamado de triangulação. Ainda foram utilizados extensômetros elétricos para estimar deformações pontuais na geomembrana. A fim de prevenir o puncionamento da geomembrana e limitar a sua deformação, utilizou-se como camada de proteção quatro geotêxteis não tecidos do tipo PP com massa por unidade de área variando entre 550 e 1300 g/m2, e uma camada de 10 cm de argila. Para a carga de 600 kPa, todas as camadas de proteção foram eficientes para evitar o puncionamento da geomembrana e limitar a sua deformação em 6%. Na carga de 1800 kPa, para proteção de geotêxtil, as configurações duplas tiveram melhor desempenho com valores de deformações menores que 6%, e a camada de 10 cm de argila foi ainda mais eficaz. Por fim, o trabalho mostrou que a superfície deformada decorrente do tipo de proteção adotado também é influenciada pelo grau de compactação do solo, o tipo de brita, a carga aplicada e as propriedades físicas do elemento de proteção. / In landfill backfill systems and mining tailings piles, it is common to use nonwoven geotextiles to protect geomembrane punctures by sharp objects such as gravel. In this work, an experimental study was carried out to evaluate the deformed HDPE geomembrane surface, with a thickness of 2 mm, under a protective layer subjected to loads of 600 kPa and 1800 kPa over 100 h, with the objective of Simulate mechanical damage of operation. To read the deformed surface of the geomembrane was used a sheet of lead located under the geomembrane and its deformations were estimated from a machine of reading by coordinates, with grid of 4 mm. Also, the deformed surface of the geomembrane was estimated for the grid of 1 mm, with the application of the interpolation method called triangulation. Electrical extensometers were also used to estimate point deformations in the geomembrane. In order to prevent the puncture of the geomembrane and to limit its deformation, four non-woven PP-type geotextiles with a mass per unit area ranging from 550 to 1300 g/m2 and a layer of 10 cm of clay. At the load of 600 kPa, all the layers of protection were efficient to avoid the puncture of the geomembrane and to limit its deformation in 6%. In the vertical load of 1800 kPa, for geotextile protection, the double configurations had better performance with deformation values lower than 6%, and the 10 cm layer of clay was even more effective. Finally, the work showed that the deformed surface resulting from the type of protection adopted is also influenced by the degree of soil compaction, the type of gravel, the applied load and the physical properties of the protection element.

Nos sistemas de revestimento de fundo de aterros sanitários e pilhas de rejeito de mineração, é comum utilizar geotêxtil não-tecido para a proteção ao puncionamento da geomembrana por objetos pontiagudos como a brita. Neste trabalho, realiza-se um estudo experimental a fim de avaliar a superfície deformada de geomembrana de PEAD, com 2 mm de espessura, em camada de proteção sujeita a carregamentos de 600 kPa e 1800 kPa ao longo de 100 h, com o objetivo de simular danos mecânico de operação. Para a leitura da superfície deformada da geomembrana utilizou-se um lençol de chumbo localizado sob a geomembrana e as suas deformações foram estimadas a partir de uma máquina de leitura por coordenadas, com grid de 4 mm. Além deste, foi estimada a superfície deformada da geomembrana para o grid de 1 mm, com a aplicação do método de interpolação chamado de triangulação. Ainda foram utilizados extensômetros elétricos para estimar deformações pontuais na geomembrana. A fim de prevenir o puncionamento da geomembrana e limitar a sua deformação, utilizou-se como camada de proteção quatro geotêxteis não tecidos do tipo PP com massa por unidade de área variando entre 550 e 1300 g/m2, e uma camada de 10 cm de argila. Para a carga de 600 kPa, todas as camadas de proteção foram eficientes para evitar o puncionamento da geomembrana e limitar a sua deformação em 6%. Na carga de 1800 kPa, para proteção de geotêxtil, as configurações duplas tiveram melhor desempenho com valores de deformações menores que 6%, e a camada de 10 cm de argila foi ainda mais eficaz. Por fim, o trabalho mostrou que a superfície deformada decorrente do tipo de proteção adotado também é influenciada pelo grau de compactação do solo, o tipo de brita, a carga aplicada e as propriedades físicas do elemento de proteção. / In landfill backfill systems and mining tailings piles, it is common to use nonwoven geotextiles to protect geomembrane punctures by sharp objects such as gravel. In this work, an experimental study was carried out to evaluate the deformed HDPE geomembrane surface, with a thickness of 2 mm, under a protective layer subjected to loads of 600 kPa and 1800 kPa over 100 h, with the objective of Simulate mechanical damage of operation. To read the deformed surface of the geomembrane was used a sheet of lead located under the geomembrane and its deformations were estimated from a machine of reading by coordinates, with grid of 4 mm. Also, the deformed surface of the geomembrane was estimated for the grid of 1 mm, with the application of the interpolation method called triangulation. Electrical extensometers were also used to estimate point deformations in the geomembrane. In order to prevent the puncture of the geomembrane and to limit its deformation, four non-woven PP-type geotextiles with a mass per unit area ranging from 550 to 1300 g/m2 and a layer of 10 cm of clay. At the load of 600 kPa, all the layers of protection were efficient to avoid the puncture of the geomembrane and to limit its deformation in 6%. In the vertical load of 1800 kPa, for geotextile protection, the double configurations had better performance with deformation values lower than 6%, and the 10 cm layer of clay was even more effective. Finally, the work showed that the deformed surface resulting from the type of protection adopted is also influenced by the degree of soil compaction, the type of gravel, the applied load and the physical properties of the protection element.

The work in this thesis is concerned with the mechanics of the initiation and growth of small fatigue cracks from notches under service load histories. Fatigue life estimates for components subjected to variable amplitude service loading are usually based on the same constant amplitude strain-life data used for constant amplitude fatigue life predictions. The resulting fatigue life estimates although they are accurate for constant amplitude fatigue, are always non conservative for variable amplitude load histories. Similarly fatigue life predictions based on small crack growth calculations for cracks growing from flaws in notches are non conservative when constant amplitude crack growth data are used. These non conservative predictions have, in both cases, been shown to be due to severe reductions in fatigue crack closure arising from large (overload or underload) cycles in a typical service load history. Smaller load cycles following a large near yield stress overload or underload cycle experience a much lower crack opening stress than that experienced by the same cycles in the reference constant amplitude fatigue tests used to produce design data. This reduced crack opening stress results in the crack remaining open for a larger fraction of the stress-strain cycle and thus an increase in the effective portion of the stress-strain cycle. The effective strain range is increased and the fatigue damage for the small cycles is greater than that calculated resulting in a non conservative fatigue life prediction. Previous work at Waterloo introduced parameters based on effective strain-life fatigue data and effective stress intensity versus crack growth rate data. Fatigue life calculations using these parameters combined with experimentally derived crack opening stress estimates give accurate fatigue life predictions for notched components subjected to variable amplitude service load histories. Information concerning steady state crack closure stresses, effective strain-life data, and effective stress intensity versus small crack growth rate data, are all obtained from relatively simple and inexpensive fatigue tests of smooth specimens in which periodic underloads are inserted into an otherwise constant amplitude load history. The data required to calibrate a variable amplitude fatigue crack closure model however, come from time consuming measurements of the return of crack closure levels for small cracks to a steady state level following an underload (large cracks for which crack closure measurements are easier to make cannot be used because at the high stress levels in notches under service loads a test specimen used would fracture). For low and moderately high hardness levels in metals crack growth and crack opening stress measurements have been made using a 900x optical microscope for the small crack length at which a test specimen can resist the high stress levels encountered when small cracks grow from notches. For very hard metals the crack sizes may be so small that the measurements must be made using a confocal scanning laser microscope. In this case the specimen must be removed from the test machine for each measurement and the time to acquire data is only practical for an extended research project. The parameters for the crack closure model relating to steady state crack closure levels vary with material cyclic deformation resistance which in turn increases with hardness. One previous investigation found that the steady state crack opening level was lower and the recovery to a steady state crack opening stress level after an underload was more rapid for a hard than for a soft metal. This observation can be explained by the dependence of the crack tip plastic zone size that determines crack tip deformation and closure level on metal hardness and yield strength. Further information regarding this hypothesis has been obtained in this thesis by testing three different steels of varying hardness levels (6 HRC, 35 HRC, and 60 HRC) including a very hard carburized steel having a hardness level (60 HRC) for which no crack opening stress data for small cracks had yet been obtained. This thesis introduced a new test procedure for obtaining data on the return of crack opening stress to a steady state level following an underload. Smooth specimens were tested under load histories with intermittent underload cycles. The frequency of occurrence of the underloads was varied and the changes in fatigue life observed. The changes in damage per block (the block consisted of an underload cycle followed by intermittent small cycles) were used to determine the value of the closure model parameter governing the recovery of the crack opening stress to its steady state level. Concurrent tests were carried out in which the crack opening stress recovery was measured directly on crack growth specimens using optical microscope measurements. These tests on metals ranging in hardness from soft to very hard were used to assess whether the new technique would produce good data for crack opening stress changes after underloads for all hardness levels. The results were also used to correlate crack closure model parameters with mechanical properties. This together with the steady state crack opening stress, effective strain-life data and the effective intensity versus crack growth rate data obtained from smooth specimen tests devised by previous researchers provided all the data required to calibrate the two models proposed in this investigation to perform strain-life and small crack growth fatigue analysis.

With sufficient time, a high density polyethylene geomembrane will degrade and lose its engineering properties until ruptures signal the end of its service-life. This thesis examines the longevity of nine different geomembranes; five of them were of different thickness manufactured from the same resin. The degradation of properties and time to failure are investigated for geomembranes: in immersion tests; as a part of a landfill composite liner; and, exposed to the elements. The different thermal and stress histories associated with manufacturing geomembranes of different thickness are shown to affect their morphological structure; consequently, their stress crack resistance. When immersed in synthetic leachate, it was found that: (a) thicker geomembranes have a longer antioxidants depletion time but the effect of thickness decreases with temperature and is less than expected; (b) inferences of geomembrane’s longevity based on its initial properties may be misleading because a geomembrane may chemically degrade (as manifested by the change in melt index) despite the presence of a significant amount of stabilizers (as manifested by the measured high pressure oxidative induction time); and, (c) stress crack resistance may change before antioxidant depletion or chemical degradation takes place, likely, due to changes in geomembrane morphological structure with the maximum decrease being observed at 55oC. Reductions also were measured for geomembrane immersed in air and water at 55oC. The geomembrane aged in a simulated landfill liner at 85oC is shown to have service-life as little as three years with 30,000 to >2.0 million ruptures/hectare at failure. For exposed geomembranes in Alumbrera (Argentina), samples were exhumed from two mine facilities after ~16 years of exposure. The antioxidants in exposed samples depleted to residual and the stress crack resistance had dropped to as low as 70 hours. Samples were exhumed from a different exposed geomembrane in a test site in Godfrey (Canada) after six years of exposure. The antioxidants were partially depleted, with depletion to residual projected to take at least 20 years; however, despite no evidence of chemical ageing, the stress crack resistance had decreased from 330 to 190 hours, likely due to changes in the morphological structure of the geomembrane. / Thesis (Ph.D, Civil Engineering) -- Queen's University, 2014-02-28 04:59:20.834

The work in this thesis is concerned with the mechanics of the initiation and growth of small fatigue cracks from notches under service load histories. Fatigue life estimates for components subjected to variable amplitude service loading are usually based on the same constant amplitude strain-life data used for constant amplitude fatigue life predictions. The resulting fatigue life estimates although they are accurate for constant amplitude fatigue, are always non conservative for variable amplitude load histories. Similarly fatigue life predictions based on small crack growth calculations for cracks growing from flaws in notches are non conservative when constant amplitude crack growth data are used. These non conservative predictions have, in both cases, been shown to be due to severe reductions in fatigue crack closure arising from large (overload or underload) cycles in a typical service load history. Smaller load cycles following a large near yield stress overload or underload cycle experience a much lower crack opening stress than that experienced by the same cycles in the reference constant amplitude fatigue tests used to produce design data. This reduced crack opening stress results in the crack remaining open for a larger fraction of the stress-strain cycle and thus an increase in the effective portion of the stress-strain cycle. The effective strain range is increased and the fatigue damage for the small cycles is greater than that calculated resulting in a non conservative fatigue life prediction. Previous work at Waterloo introduced parameters based on effective strain-life fatigue data and effective stress intensity versus crack growth rate data. Fatigue life calculations using these parameters combined with experimentally derived crack opening stress estimates give accurate fatigue life predictions for notched components subjected to variable amplitude service load histories. Information concerning steady state crack closure stresses, effective strain-life data, and effective stress intensity versus small crack growth rate data, are all obtained from relatively simple and inexpensive fatigue tests of smooth specimens in which periodic underloads are inserted into an otherwise constant amplitude load history. The data required to calibrate a variable amplitude fatigue crack closure model however, come from time consuming measurements of the return of crack closure levels for small cracks to a steady state level following an underload (large cracks for which crack closure measurements are easier to make cannot be used because at the high stress levels in notches under service loads a test specimen used would fracture). For low and moderately high hardness levels in metals crack growth and crack opening stress measurements have been made using a 900x optical microscope for the small crack length at which a test specimen can resist the high stress levels encountered when small cracks grow from notches. For very hard metals the crack sizes may be so small that the measurements must be made using a confocal scanning laser microscope. In this case the specimen must be removed from the test machine for each measurement and the time to acquire data is only practical for an extended research project. The parameters for the crack closure model relating to steady state crack closure levels vary with material cyclic deformation resistance which in turn increases with hardness. One previous investigation found that the steady state crack opening level was lower and the recovery to a steady state crack opening stress level after an underload was more rapid for a hard than for a soft metal. This observation can be explained by the dependence of the crack tip plastic zone size that determines crack tip deformation and closure level on metal hardness and yield strength. Further information regarding this hypothesis has been obtained in this thesis by testing three different steels of varying hardness levels (6 HRC, 35 HRC, and 60 HRC) including a very hard carburized steel having a hardness level (60 HRC) for which no crack opening stress data for small cracks had yet been obtained. This thesis introduced a new test procedure for obtaining data on the return of crack opening stress to a steady state level following an underload. Smooth specimens were tested under load histories with intermittent underload cycles. The frequency of occurrence of the underloads was varied and the changes in fatigue life observed. The changes in damage per block (the block consisted of an underload cycle followed by intermittent small cycles) were used to determine the value of the closure model parameter governing the recovery of the crack opening stress to its steady state level. Concurrent tests were carried out in which the crack opening stress recovery was measured directly on crack growth specimens using optical microscope measurements. These tests on metals ranging in hardness from soft to very hard were used to assess whether the new technique would produce good data for crack opening stress changes after underloads for all hardness levels. The results were also used to correlate crack closure model parameters with mechanical properties. This together with the steady state crack opening stress, effective strain-life data and the effective intensity versus crack growth rate data obtained from smooth specimen tests devised by previous researchers provided all the data required to calibrate the two models proposed in this investigation to perform strain-life and small crack growth fatigue analysis.

La tesis se enmarca en la caracterización, a nivel material, de la fractura del hormigón reforzado con fibras de acero (SFRC) bajo solicitaciones de tracción y cortante, y sobre la determinación de parámetros que representan la tenacidad del material sometido a esos dos modos de carga. Asimismo, se han realizado ensayos hasta rotura por cortante de elementos estructurales a escala real, los cuales se han analizado utilizando formulaciones existentes en distintos códigos de diseño.El comportamiento a tracción uniaxial del hormigón reforzado con fibras de acero se caracteriza utilizando cilindros entallados, elaborados con hormigones de resistencia normal y alta, con y sin fibras de acero. La metodología se extiende también para testigos extraídos de elementos de mayor tamaño. Los resultados se utilizan para definir parámetros de tenacidad y resistencia equivalentes de post-pico utilizables para representar el comportamiento del material y para un posible diseño estructural. Además, se desarrolla un estudio paramétrico experimental, que considera diferentes variables del ensayo y forma de probetas, para definir una configuración confiable del ensayo. Se analizan los modos de rotura observados y se evalúa la respuesta tensión-ancho de fisura. Asimismo, se propone una relación tensión-apertura de fisura característica para el diseño y análisis estructural. El comportamiento a tracción uniaxial se compara también con el de flexión y tracción por compresión diametral.La fractura por cortante se estudia a nivel material, en hormigones de resistencia normal y alta, con y sin fibras de acero, utilizando la configuración de cortante directo denominada push-off. Se analizan el modo de rotura y la respuesta tensión-desplazamiento. Además, se definen parámetros basados en la tenacidad y tensiones equivalentes de cortante para una posible utilización en el diseño estructural.Con el fin de obtener resultados que validen la utilización de las fibras de acero como refuerzo de cortante y al mismo tiempo estudiar la fractura por cortante a nivel estructural, se han realizado ensayos a escala real sobre vigas de sección rectangular y en T. Se analizan las respuestas carga-flecha y carga-ancho de fisura de vigas rectangulares de hormigón reforzado con fibras de acero variando su altura y de vigas T variando las dimensiones del ala. Los resultados obtenidos experimentalmente se utilizan para verificar la aplicabilidad de los métodos de diseño existentes en el caso del hormigón reforzado con fibras de acero. Además, se presenta una propuesta para el diseño a cortante basada en la respuesta tensión-desplazamiento relativo obtenida a partir del ensayo push-off de cortante directo. / The thesis deals with the characterization of the failure of steel fiber reinforced concrete (SFRC) in tension and shear, on the material level, and the determination of parameters that represent the toughness in these two modes of failure. Tests have been performed on large-scale beams failing under shear failure, which have been analyzed using existing design code formulas. The toughness parameters determined from the material are used in the design against such failure.The uniaxial tensile behavior of SFRC is characterized using notched cylinders of normal and high strength concretes, with and without steel fibers. The methodology is also extended to cores extracted from large elements. Results are used to define toughness parameters and equivalent post-peak strengths to be used for representing the material behavior and for possible structural design. Furthermore, a parametric study considering different test variables and specimen shape is carried out in order to define a reliable test configuration. The observed modes of failure are analyzed and the stress-crack width response is evaluated. Also, a characteristic stress-crack width response is proposed for structural analysis and design. The uniaxial tension behavior is also compared with that of flexural and splitting-tension.The shear failure is studied using the direct shear push-off test configuration, in normal and high strength concretes with and without steel fibers. The mode of failure and the stress-slip and stress-crack opening responses are analyzed. Toughness parameters and equivalent shear strengths based on the test results are defined for structural design.In order to provide results for validating the use of steel fibers as shear reinforcement and for studying shear failure at the structural level, full-scale tests on rectangular and T-beams were performed. The load-deflection and load-crack width responses are analyzed and compared with results of plain concrete beam tests. The experimentally-obtained results are used to evaluate the applicability of existing design methods for steel fiber reinforced concrete. Furthermore, a proposal for shear design based on the shear stress versus slip relationship from the push-off shear test is presented.

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 BFUP / Ultra 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 UHPFRC

Devido à fragilidade do concreto, o controle e combate da fissuração são de importância fundamental em estruturas de concreto armado. Uma maneira de melhorar as propriedades do concreto à tração é pelo emprego de fibras. A presente pesquisa é uma tentativa de fornecer diretrizes para o dimensionamento de estruturas de concreto armado com fibras, e armadura convencional sob condições de serviço. Apresenta-se inicialmente, um estudo do comportamento do material à tração. Um modelo probabilístico/micro-mecânico fundamentado na mecânica de fratura, e capaz de prever o comportamento pós-fissuração do compósito é apresentado. O modelo prevê a relação tensão-abertura de fissura do compósito levando em conta os seguintes micro-mecanismos: travejamento de agregado e fibras, a ruptura das fibras, os efeitos de: atrito local (snubbing effect), esmagamento da matriz, Cook-Gordon, e da pré-tração das fibras. Em nível estrutural, dois modelos macro-mecânicos são apresentados. O primeiro modelo tem premissa na teoria clássica de fissura, e o segundo na mecânica de dado. O primeiro modelo é ajustado para aplicação na previsão de espaçamento e aberturas de fissura em estruturas de concreto armado com fibras discretas e aleatoriamente dispostas. É demostrado que o modelo micro-mecânico pode alimentar perfeitamente o modelo macro-mecânico. Ensaios de tração com elementos de placas de argamassa com fibras armada com tela ou fios foram realizados. Os resultados teóricos previstos pelo modelo foram comparados com os obtidos do programa experimental, e mostram uma boa concordância, comprovando a validade do modelo apresentado. / Due to the brittleness of concrete, the control and prevention of cracking in reinforced concrete structures are of prime importance. One way of improving the tensile properties of concrete is by the addition of fibres. The present research is a trial to provide guidelines for the design of fibre reinforced concrete structures under service loads. First of all, a study of the tensile behaviour of the composite material is presented. A probabilistic/fracture mechanics based micromechanical model, capable of predicting the poscracking behaviour of the material is presented. The model predicts the tensile stress-crack width relationship, accounting for the following micromechanisms: fibre and aggregate bridging, fibre rupture, local snubbing, matrix spalling, the Cook-Gordon interface effect, and fibre prestressing. At the structural level, two macromechanical models are presented. One is founded on the classical theory of cracking, while the other, a shear lag model, is founded on the continuum damage mechanics. The first model is adjusted for application to the prevision of crack width and crack spacing in fibre reinforced concrete structures with short discrete and randomly dispersed fibres. It is shown that the micromechanical model fits very well in the macrostructural model. Tensile tests with mortar specimens reinforced with continuous steel wires or meshes and PVA or polypropylene fibres were carried out. The theoretical results predicted by the model were compared with results obtained from the experimental program, and show very good agreement, confirming the validity of the theoretical model.

Devido à fragilidade do concreto, o controle e combate da fissuração são de importância fundamental em estruturas de concreto armado. Uma maneira de melhorar as propriedades do concreto à tração é pelo emprego de fibras. A presente pesquisa é uma tentativa de fornecer diretrizes para o dimensionamento de estruturas de concreto armado com fibras, e armadura convencional sob condições de serviço. Apresenta-se inicialmente, um estudo do comportamento do material à tração. Um modelo probabilístico/micro-mecânico fundamentado na mecânica de fratura, e capaz de prever o comportamento pós-fissuração do compósito é apresentado. O modelo prevê a relação tensão-abertura de fissura do compósito levando em conta os seguintes micro-mecanismos: travejamento de agregado e fibras, a ruptura das fibras, os efeitos de: atrito local (snubbing effect), esmagamento da matriz, Cook-Gordon, e da pré-tração das fibras. Em nível estrutural, dois modelos macro-mecânicos são apresentados. O primeiro modelo tem premissa na teoria clássica de fissura, e o segundo na mecânica de dado. O primeiro modelo é ajustado para aplicação na previsão de espaçamento e aberturas de fissura em estruturas de concreto armado com fibras discretas e aleatoriamente dispostas. É demostrado que o modelo micro-mecânico pode alimentar perfeitamente o modelo macro-mecânico. Ensaios de tração com elementos de placas de argamassa com fibras armada com tela ou fios foram realizados. Os resultados teóricos previstos pelo modelo foram comparados com os obtidos do programa experimental, e mostram uma boa concordância, comprovando a validade do modelo apresentado. / Due to the brittleness of concrete, the control and prevention of cracking in reinforced concrete structures are of prime importance. One way of improving the tensile properties of concrete is by the addition of fibres. The present research is a trial to provide guidelines for the design of fibre reinforced concrete structures under service loads. First of all, a study of the tensile behaviour of the composite material is presented. A probabilistic/fracture mechanics based micromechanical model, capable of predicting the poscracking behaviour of the material is presented. The model predicts the tensile stress-crack width relationship, accounting for the following micromechanisms: fibre and aggregate bridging, fibre rupture, local snubbing, matrix spalling, the Cook-Gordon interface effect, and fibre prestressing. At the structural level, two macromechanical models are presented. One is founded on the classical theory of cracking, while the other, a shear lag model, is founded on the continuum damage mechanics. The first model is adjusted for application to the prevision of crack width and crack spacing in fibre reinforced concrete structures with short discrete and randomly dispersed fibres. It is shown that the micromechanical model fits very well in the macrostructural model. Tensile tests with mortar specimens reinforced with continuous steel wires or meshes and PVA or polypropylene fibres were carried out. The theoretical results predicted by the model were compared with results obtained from the experimental program, and show very good agreement, confirming the validity of the theoretical model.