Ageing infrastructure that is shear deficient and may be at risk of brittle collapse, particularly in seismically active regions, can be economically strengthened using externally bonded fibre-reinforced polymers (FRP). Although many studies have been conducted on small-scale specimens subject to monotonic loading, little experimental data exists for large-scale specimens and those tested under reversed cyclic loading to simulate a seismic event. An experimental study of large-scale (400 mm x 650 mm) beam specimens strengthened in shear with FRP was conducted to examine the effects of reversed cyclic loading and to quantify material shear strength contributions. Testing showed that FRP retrofits were highly effective at improving shear performance and were not adversely affected by reversed cyclic loading prior to the occurrence of flexural yielding. The shear resistance attributed to concrete was found to remain relatively consistent with reversed cyclic loading prior to flexural yielding, after which point concrete strength decay was apparent. The loss of concrete shear resistance directly influenced the rate of FRP straining and the achievable ductility. An analytical model using the Modified Compression Field Theory (MCFT) was developed for externally bonded FRP reinforcement to describe the experimental behaviour and to evaluate the accuracy of current FRP design methods. Failures were accurately modelled when appropriate FRP strain limits were used for the ultimate strength and for the stress transfer capacity across the shear crack. Proposed FRP strain limits were developed considering the strain distribution along the crack plane. In addition, improved strain limits incorporate the effect of rupture failure due to stress concentrations in the FRP wrapped around the beam corners. The proposed FRP formulations offer improved accuracy over the current FRP design methods (CSA S6-06 and ACI 440.2R-08), which suggest a broadly applied maximum strain limit of 0.004 mm/mm, which was determined to be overly conservative for FRP rupture failures.

No description available.

No description available.

Předložená disertační práce se zabývá zesílením kruhových železobetonových sloupů pomocí vlákny vyztužených polymerů (tzv. FRP – fibre reinforced polymer) namáhaných laterálním cyklickým zatížením. Tato výzkumná studie se zaměřuje na zkoumání využití FRP tkaniny pro dodatečné zesílení, zlepšení chování kruhových železobetonových sloupů a vytvoření návrhového algoritmu pro zesílení kruhového sloupu pomocí kompozitních FRP materiálů. Návrhový algoritmus byl odvozen na základě analytické studie, numerických simulací a výsledků experimentální činnosti. Na základě těchto výsledků byl navržen postup pro návrh zesílení sloupů ovinutím, který předpovídá chování železobetonových sloupů vystavených laterálním cyklickým zatížením. Při experimentální práci byly zkušební vzorky zatíženy současně axiální sílou a příčným cyklickým zatížením. Toto bylo provedeno dvěma různými způsoby. První způsob zatěžování byl proveden konstantní velikostí laterální síly po daný počet cyklů (1 milion) se sledováním změny deformace. A druhý způsob provedení spočíval v zatížení konstantní deformací se sledováním úbytku síly během zatěžovací zkoušky. Dizertační práce rovněž předkládá přehled současného stavu poznání zesílení železobetonových kruhových sloupů ovinutím FRP tkaninou vystavených působení seismického zatížení. Dále uvádí přehled návrhových metodik a normová ustanovení Eurokódu a ACI. Experimentální program byl proveden za účelem ověření chování ovinutých kruhových sloupů při působení laterálního cyklického zatížení. Závěr práce sumarizuje poznatky o chování sloupů zesílených ovinutím FRP tkaninou při působení laterálního cyklického zatížení a představuje empirický model pro návrh zesílení ovinutím při vysokém a nízkém cyklickém zatížení.

Protection of buried pipes is a serious issue that concerns countries around the world. Therefore, there is a need for new soil improvement techniques such as geosynthetic materials installation to protect these pipes from damage. This study used large-scale laboratory tests to study the behaviour of buried pipes. A total of 22 large-scale tests were performed to study the behaviour of buried flexible HDPE pipes with and without void presence under the protection of the geogrid reinforcing layers subjected to incrementally increasing cyclic loading. The presence of voids located at the spring-line of the flexible buried pipes, led to a considerable increase in the soil surface settlement, pressure recorded at the pipe crown, spring-line and invert, pipe deformation and strain recorded in the pipe wall. Increasing the pipe burial depth contributed to significant reductions in the soil surface settlement, pressure recorded at the pipe crown and invert, pipe deformation and strain recorded in the pipe wall. However, the void presence limited the contribution of increasing the pipe burial depth. The inclusion of a geogrid reinforcing layer contributed to a considerable reduction in the soil surface settlement, pressure recorded at the pipe crown, spring-line and invert, pipe deformation and strain recorded in the pipe wall. The use of a combination of geogrid reinforcing layers and increasing the pipe burial depth contributed in diminishing the ground void presence effect, where better pressure distribution inside the system was achieved. Consequently, more protection was provided to the buried pipe.

O objetivo principal do trabalho é analisar o comportamento experimental e teórico de vigas de concreto armado de modo a quantificar a perda de rigidez global através do cálculo de flechas sucessivas ocorridas durante a aplicação de carregamento cíclico, em regime de serviço. A ênfase da pesquisa é dada à análise numérica; a aderência na interface aço-concreto é tratada com uma estratégia onde cada parte é modelada isoladamente de modo a se considerar o contato entre a barra de aço (com o desenho de suas nervuras) e o concreto envolvente. A análise numérica foi feita com o auxílio do aplicativo ABAQUS, baseado no método dos elementos finitos. O modelo constitutivo usado para o concreto é fundamentado na mecânica do dano contínuo. Foram realizados ensaios experimentais com espécimes de concreto contendo uma barra de aço colocada em seu eixo e, também, com vigas de concreto armado sub-armadas e com armadura dupla, com seção transversal retangular e tipo T. Comparações dos resultados obtidos nos ensaios experimentais com as respostas da análise numérica são apresentadas e discutidas. Ao final, propõem-se expressões que quantificam a perda de rigidez em função do número de ciclos aplicado. / The main purpose of this research is to analyze the experimental and theoretical behavior of reinforced concrete beams, in order to quantify the stiffness loss, by calculating successive deflections during the cyclic loads application, under service loads. The emphasis of this research is the numerical analysis. The modeling of steel-concrete interface is done taking into account the contact between the steel bars (with their ribs) and the concrete surrounding the bars. The numerical analysis was made by using the software ABAQUS, based on the finite element method. The concrete’s constitutive model is based on the continuous damage mechanics. The experimental tests were made with cylinder concrete specimens with an axial bar and rectangular and T cross section reinforced concrete beams, where some had only tension reinforcement and others had tension and compression reinforcement. Comparisons between experimental and numerical results are presented and discussed. At the end expressions to quantify the stiffness loss due to number of cycles are proposed.

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O objetivo principal do trabalho é analisar o comportamento experimental e teórico de vigas de concreto armado de modo a quantificar a perda de rigidez global através do cálculo de flechas sucessivas ocorridas durante a aplicação de carregamento cíclico, em regime de serviço. A ênfase da pesquisa é dada à análise numérica; a aderência na interface aço-concreto é tratada com uma estratégia onde cada parte é modelada isoladamente de modo a se considerar o contato entre a barra de aço (com o desenho de suas nervuras) e o concreto envolvente. A análise numérica foi feita com o auxílio do aplicativo ABAQUS, baseado no método dos elementos finitos. O modelo constitutivo usado para o concreto é fundamentado na mecânica do dano contínuo. Foram realizados ensaios experimentais com espécimes de concreto contendo uma barra de aço colocada em seu eixo e, também, com vigas de concreto armado sub-armadas e com armadura dupla, com seção transversal retangular e tipo T. Comparações dos resultados obtidos nos ensaios experimentais com as respostas da análise numérica são apresentadas e discutidas. Ao final, propõem-se expressões que quantificam a perda de rigidez em função do número de ciclos aplicado. / The main purpose of this research is to analyze the experimental and theoretical behavior of reinforced concrete beams, in order to quantify the stiffness loss, by calculating successive deflections during the cyclic loads application, under service loads. The emphasis of this research is the numerical analysis. The modeling of steel-concrete interface is done taking into account the contact between the steel bars (with their ribs) and the concrete surrounding the bars. The numerical analysis was made by using the software ABAQUS, based on the finite element method. The concrete’s constitutive model is based on the continuous damage mechanics. The experimental tests were made with cylinder concrete specimens with an axial bar and rectangular and T cross section reinforced concrete beams, where some had only tension reinforcement and others had tension and compression reinforcement. Comparisons between experimental and numerical results are presented and discussed. At the end expressions to quantify the stiffness loss due to number of cycles are proposed.

Le dimensionnement en fatigue à grand nombre de cycles d'un contact roulant entre des éléments ayant subi un traitement thermochimique de cémentation s'avère rapidement complexe.D'une part le traitement de cémentation apporte une hétérogénéité de propriété dans les couches supérieures de la pièce qui dépend du protocole utilisé. D'autre part le chargement de contact roulant est un chargement complexe dont le mode de défaillance en fatigue s'initie en sous-couche.Afin de limiter le temps de la caractérisation des champs de propriétés en fatigue, l'utilisation des mesures d'auto-échauffement sous sollicitation cyclique ainsi que leur interprétation par un modèle probabiliste à deux échelles est proposé. Néanmoins de par l'hétérogénéité du matériau et de par la particularité du chargement il peut s'avérer délicat d'appliquer une telle méthode d'évaluation. ll est alors proposé d'explorer ces deux difficultés de manière séparé.Pour prendre en compte l'hétérogénéité matériaux, un protocole d'analyse de courbe d'auto-échauffement basé sur une variante d'un modèle probabiliste à deux échelles et sur les mesures de taux de carbone a été proposé. Les paramètres du modèle ont été identifiés sur une classe d'acier via des mesures d'auto-échauffement réalisées sur des éprouvettes représentatives de l'hétérogénéité du au traitement de cémentation. Enfin le modèle a été validé par comparaison avec des points de fatigue expérimentaux.En ce qui concerne le chargement de contact roulant, les difficultés pour réaliser une mesure d'auto-échauffement ont mené à effectuer une première campagne de mesure sur le cas intermédiaire du contact répété. A l'aide d'un modèle analytique simple, l'évolution du champ de température a pu être reliée à un terme source de chaleur moyen dont le lien avec les mécanismes de fatigue reste à démontrer. Finalement, des prototypes de machine de contact roulant dédiés aux mesures d'auto-échauffement ont été proposés. Les mesures réalisées sur ces dernières et leur interprétation laissent à penser qu'il sera possible d'identifier des propriétés de fatigue à partir de mesure d'auto-échauffement. / The rolling contact fatigue prediction between two carburizing part quickly becomes complex.On one hand, the carburizing treatment give heterogeneous properties in surface layer depending on the treatment protocol. On the other hand, the rolling contact load is a complex load with a fatigue initiation in the sub-layer. To limit the duration of the field fatigue properties characterization, self-heating measurements under cycle load are used and their interpretation by a probabilistic two scales model is proposed. Nevertheless applying this fatigue evaluation method on heterogeneous material and for rolling contact load can be difficult. ln first approach those difficulties are split.To take into account the material heterogeneity, an analysis based on a variation of one probabilistic two scales model and on carbon rate measurement is proposed. Model parameters are identified on one steel class with self-heating measurement made on specimens representative of carburizing material heterogeneity. Finally the model is validated by comparison with experimental fatigue point.Making self-heating measurement for rolling contact load is complex. Consequently a first self-heating measurement campaign is made on the intermediary case of repeated contact. With a simple analytic model, the temperature field evolution can be linked to a mean heat source whose link with fatigue mechanism must be proven. Finally, rolling contact machine prototypes are proposed. Self-heating measurement made on those prototypes and their interpretation suggest that it will be possible to identify fatigue properties with self-heating measurement.

Pour fabriquer le caisson-coeur du futur réacteur expérimental Jules Horowitz (RJH), un assemblage de viroles est effectué à l'aide d'un procédé haute énergie : le soudage par faisceau d'électrons (FE). L'aluminium 6061-T6 qui a été choisi pour la fabrication de ces viroles est un alliage à durcissement structural, ce qui signifie que ses propriétés mécaniques sont très fortement dépendantes de son état de précipitation. Lors du soudage des viroles, l'état microstructural du matériau est affecté : on assiste notamment à une dégradation de l'état fin de précipitation (T6). Les conséquences de cette dégradation microstructurale sont diverses. Notamment, l'évolution de l'état de précipitation au cours du soudage engendre une variation du comportement mécanique et impactera donc la distribution des contraintes résiduelles. De plus, les propriétés mécaniques en service à proximité du joint soudé seront grandement modifiées, on assiste par exemple à une chute de la limite d'élasticité. Dans ce travail, des essais cycliques ont été effectués après des chargements thermiques représentatifs d'une opération de soudage mais aussi pendant des essais isothermes. L'analyse de ces résultats et la confrontation à des mesures de Diffusion de Neutrons aux Petits Angles (DNPA) et de Microscopie Electronique en Transmission (MET) permettent de comprendre les effets de la précipitation sur la loi de comportement de l'alliage. Afin de prédire les évolutions microstructurales et mécaniques dans l'alliage 6061, un logiciel de précipitation a été implémenté et couplé à un modèle élastoplastique à base physique. Les résultats obtenus permettent de représenter la grande variété de comportement observé lors de la campagne expérimentale. Un couplage entre simulation éléments finis thermique et précipitation a été effectué et permet d'ouvrir des perspectives de simulations plus physiques pour ce type d'alliage. / In order to assemble the pressure vessel of experimental Reactor Jules Horowitz (RJH) of France in the future, the electron beam welding process will be used. Several ferrules in a 6061-T6 age hardening aluminum alloy are used for manufacturing this vessel. The fine precipitation state (T6) is affected significantly by the electron beam welding process. Consequently, this microstructural degradation leads to an evolution of the mechanical behaviour and thus will affect the distribution of residual stresses. Moreover, the mechanical properties of the weld joint at ambiant temperature can be modified, such as the yield stress that may drop from 280 MPa to 55 MPa. In this work, cyclic tensile tests have been performed after anisothermal histories representative of welding and during isothermal treatments. The analysis of these results is compared with Small Angles Neutrons Scattering (SANS) and Transmission Electron Microscopy (TEM) characterizations that allow to understand the effect of the precipitation on the material behaviour. To predict the microstructural evolutions in the 6061 structure, a precipitation model has been developped. The precipitation software "PreciSo" coupled with a Finite Element thermal simulations and elastoplastic models allows to open new prospectives in the physical-based simulations domain.