Muitas edificações têm apresentado degradação ao longo dos anos em todo o mundo, gerando situações de risco e causando acidentes, de modo que se têm estudado alternativas para se recuperar ou reforçar estruturalmente suas vigas, pilares e lajes. Entre as técnicas desenvolvidas para essas finalidades, destacam-se, atualmente, as que utilizam compósitos de polímeros reforçados com fibras (PRF), de modo que, desde as últimas décadas do século passado, desenvolveram-se os sistemas de reforço estrutural por colagem externa de tecidos e laminados de PRF de carbono (PRFC). Isto deve-se a este tipo de fibra apresentar o melhor conjunto de propriedades necessárias para se reforçarem as estruturas de concreto armado, como altas resistência à tração e módulo de elasticidade longitudinal. Na última década, surgiu o sistema de inserção de laminados de PRFC em entalhes executados no concreto de cobrimento de elementos estruturais preenchidos com resina epóxi. Embora haja resultados de outros pesquisadores, há a necessidade de maiores investigações no Brasil sobre o desempenho dessa nova técnica. Assim se propôs o planejamento experimental desta dissertação, cujo objetivo principal foi a análise experimental do desempenho de sistemas de reforço estrutural à flexão com laminados de PRFC aplicados a vigas de concreto armado ensaiadas com carregamento estático. De um total de dez vigas pré-moldadas, quatro foram testemunhos e seis foram reforçadas à flexão com dois laminados de PRFC através de três sistemas: colagem externa, inserção em entalhes longitudinais preenchidos com resina epóxi e com argamassa com sílica ativa. Analisa-se comparativamente o seu desempenho quanto às cargas máximas, aos deslocamentos verticais no centro do vão e às aberturas de fissuras. Constata-se que as reforçadas com laminados de PRFC inseridos em entalhes longitudinais preenchidos com resina epóxi apresentam os maiores valores de carga máxima e de rigidez. Entretanto as preenchidas com argamassa com sílica ativa obtêm desempenho inferior ao das vigas testemunhos por falta de aderência. Também se conclui que as reforçadas com colagem externa de laminados de PRFC têm os menores deslocamentos verticais no centro do vão. / Many buildings have shown deterioration over the years around the world, creating a hazardous situation and causing accidents, so that they have studied alternatives to recover or strengthen their structural beams, columns and slabs. Among the techniques developed for these purposes, stand out, currently, those using fiber reinforced polymer (FRP) composites. Since the last decades of the last century, it has been developed structural reinforcement systems of externally bonded carbon FRP (CFRP) textiles and laminates. This is due to the type of fiber having the best set of properties that are necessary to strengthen reinforced concrete structures, such as high tensile strength and longitudinal elastic modulus. In the last decade, the near-surface mounted CFRP laminates system executed in grooves in the concrete cover of structural elements filled with epoxy resin came up. Although there are results from other researchers, there is a need for further investigation in Brazil on the performance of this new technique. Thus, the experimental program of this thesis has been proposed, which main objective was the experimental analysis of the performance of bending structural reinforcement systems with CFRP laminates applied to reinforced concrete beams tested under static loading. From a total of ten precast beams, four were for control and six were strengthened in bending with two CFRP laminates composites through three systems: externally bonded, near-surface mounted insertion into longitudinal grooves filled with epoxy resin and mortar with silica fume. Their performance is comparatively analyzed for maximum loads, vertical displacements at mid-span and crack openings. It is concluded that those reinforced with near-surface mounted CFRP laminates inserted into longitudinal grooves filled with epoxy resin shows the highest maximum load and stiffness. However those filled with mortar with silica fume obtained lower performance than the control beams for lack of bonding. In addition, it is concluded that the ones strengthened with externally bonded CFRP laminates have the lowest mid-span vertical displacements.

Existing reinforced concrete bridges may be deemed inadequate to carry the ever-increasing traffic loads according to the current codes and standards before they reach the end of their design life. It may therefore be required to either strengthen or replace these structures, which can be costly and causes disruptions to the infrastructure. This work investigates experimentally the possibilities to extend the useful life of existing reinforced concrete slab-on-beam structures deficient in shear by means of structural strengthening with fibre-reinforced polymers (FRP). The experimental campaign involved mechanical testing of ten full-scale T-beam specimens, representative of typical existing slab-on-beam bridges. Two sizes of test specimen were used to investigate the effect of size on the ultimate shear capacity of the beams. The investigated shear-strengthening configurations included externally bonded carbon fibre reinforced polymer (CFRP) sheets in a U-wrap configuration with and without end-anchorage and deep embedded CFRP bars. Unstrengthened control specimens were also tested to provide baseline for comparison. The results from the experimental programme revealed that while the deep embedment strengthening solution provides an increase in shear capacity of up to 50%, the strengthening with CFRP U-wraps results in reduced capacity compared with the underlying control beam. This presents a major implication in terms of safe design predictions of shear capacity of reinforced concrete T-beams strengthened with CFRP sheets as this is the most commonly used shear-strengthening scheme in practice. The study also demonstrated that greater contribution from the externally bonded CFRP U-wraps can be achieved using end-anchorage systems, which delay the debonding of the CFRP. The applicability of current codes of standards and guidelines was studied as well as appropriateness of using advanced numerical methods for assessment of existing reinforced concrete structures. It was found that while the standards used for assessment greatly under-predict the shear capacity, the guidelines for FRP-strengthened beams either under- or over-predict the shear capacity of the tested beams. More accurate predictions are possible using advanced fracture mechanics-based methods for both the unstrengthened as well as the strengthened beams.

Carbon Fiber Reinforced Polymers (CFRP) are a class of advanced materials widely used in versatile applications including aerospace and automotive industries due to their exceptional physical and mechanical properties. Owing to the heterogenous nature of the composites, it is often a challenging task to machine them unlike metals. Drilling in particular, the most commonly used process for component assembly is critical especially in the aerospace sector which demands parts of highest quality and surface integrity. Conventionally, all composites are machined under dry conditions. While there are drawbacks related to dry drilling, for example, poor surface roughness, there is a need to develop processes which yield good quality parts. This thesis investigates the machining performance when drilling CFRP under cryogenic, MQL and hybrid (CryoMQL) modes and comparing with dry drilling in terms of the machining forces, delamination, diameter error and surface integrity assessment including surface roughness, hardness and sub-surface damage analysis. Additionally, the effect of varying the feed rate on the machining performance is examined. From the study, it is concluded that drilling using coolant/ lubricant outperforms dry drilling by producing better quality parts. Also, varying the feed rate proved to be advantageous over drilling at constant feed.

Cette recherche présente des résultats théoriques et expérimentaux sur le renforcement de poutres en lamellé collé par composite à base de fibres, l'application recherchée étant la proposition de structures de tabliers de ponts de haute résistance. Le concept retenu est une structure multi renforcée par la disposition de lamelles de composites entre les lamelles en bois dans la zone de traction. On montre que ce type de renfort possède expérimentalement, à taux de renfort donnée, des propriétés plus élevées que celles obtenues par des méthodes courantes consistant au renforcement en face inférieure d'une seule couche de composite. On montre en particulier que la distribution statistique de la rupture en traction du bois est resserrée grâce à la présence du composite. Ainsi, un renfort de faible épaisseur, réparti convenablement entre les lamelles de bois, a un double effet, celui attendu de diminuer les contraintes dans les fibres de bois, mais aussi, celui de réduire la distribution statistique de résistance. La prise en compte des renforts dans les calculs revient donc à redéfinir une résistance caractéristique d'un bois homogène équivalent ayant les propriétés du bois renforcé. De plus, on montre qu'il existe des configurations telles que les fissures transverses dans les lamelles de bois engendrées par la contrainte normale de traction sont stoppées par les lamelles de renfort et qu'il est possible d'obtenir un schéma de rupture multi fissuré. Un critère de rupture par délaminage de l'interface bois-composite est proposé et déterminé expérimentalement à cette fin. Enfin, des expérimentations sur prototypes hybrides constituées d'un multi couches bois-carbone-béton ultraperformant, est présentée. Les résultats ont permis de valider la méthode proposée de répartition du renfort en couches réparties de faible épaisseur.

A lightweight carbon fiber reinforced polymer (CFRP) c-channel beam was previously designed using analytical theory and finite element analysis and subsequently manufactured through a pultrusion process. Physical testing revealed the prototype did not meet the bending and torsional stiffness of the beam model. An investigation revealed that the manufactured prototype had lower fiber content than designed, compacted geometry, an altered ply layup, missing plies, and ply folds. Incorporating these changes into the beam model significantly improved model-experiment agreement. Using what was learned from the initial prototype, several new beam designs were modeled that compare the cost per weight-savings of different composite materials. The results of these models show that fiberglass is not a viable alternative to CFRP when designing for equivalent stiffness. Standard modulus carbon was shown to have slightly lower cost per-weight savings than intermediate modulus carbon, although intermediate modulus carbon saves more weight overall. Core materials, despite potential weight savings, were ruled out as they do not have the crush resistance to handle the likely clamp loads of any attaching bolts. Despite determining the ideal materials, the manufactured cost per weight-savings of the best CFRP beam design was about double the desired target. / Graduation date: 2013 / Access restricted to the OSU Community at author's request from Oct. 5, 2012 - Oct. 5, 2014

El presente trabajo se refiere al estudio teórico-experimental del comportamiento de puentes de dovelas reforzados a flexión a través de la técnica de adhesión de "Fiber Reinforcement Plastics" (FRP). Para lograr esto, se ha desarrollado un programa de investigación en el cual se incluyen 3 tipos de ensayos; caracterización de materiales, modelos reducidos y a nivel estructural, utilizando dos sistemas de refuerzo de FRP, además de comparar los resultados obtenidos en los ensayos estructurales con un modelo numérico.Los ensayos correspondientes a la fase experimental de este trabajo han sido realizados en el "Laboratorio de Tecnología de Estructuras" (LTE) de la "Escuela Técnica Superior de Ingenieros de Caminos Canales y Puertos de Barcelona" (ETSECCPB) en la "Universidad Politécnica de Cataluña" (UPC). Estos ensayos se dividieron en tres etapas principales. Se realizaron, en primer lugar, ensayos sobre vigas de dovelas con pretensado exterior que habían sido ensayadas anteriormente, reforzándolas con dos sistemas de refuerzo de FRP. En segundo lugar, se realizaron dos series de ensayos basados en probetas de adherencia para modelar la zona de juntas entre dovelas y conocer detalladamente el comportamiento de dichos sistemas de refuerzo en tales estructuras. Por último, se caracterizaron los sistemas de refuerzo para comparar las características proporcionadas por los fabricantes además de corroborar los resultados obtenidos en las dos primeras etapas de la fase experimental de este trabajo.Para poder realizar un análisis fundamentado de la fase experimental, se ha realizado una revisión bibliográfica sobre el estado del conocimiento que se enfoca a la historia de utilización de los sistemas de refuerzo mencionados anteriormente, aplicados a estructuras de hormigón, prestando especial atención en los mecanismos de falla y en específico al mecanismo denominado "peeling" así como a la adherencia del FRP al hormigón, en los cuales se centra gran parte de este trabajo de investigación.Por otra parte, se ha evaluado la eficiencia del ensayo de adherencia desarrollado, con el fin de proponerlo como herramienta para la caracterización de dichos sistemas de refuerzo en el caso de aplicación a estructuras constituidas por dovelas o en aquéllas en las que se presenten juntas de construcción.Con el fin de demostrar la validez del ensayo de adherencia, se han elegido dos sistemas de refuerzo diferentes entre si, el primero constituido por un tejido bidireccional de fibras de carbono (TFC), con un módulo de deformación relativamente bajo, en el que la resina epóxica utilizada para la adhesión del FRP al hormigón forma la matriz del mismo, y un segundo sistema formado por láminas de fibras de carbono prefabricadas (CFK), preimpregnadas de resina epóxica, con un módulo de elasticidad superior al primero, adhiriéndolo al hormigón con una resina epóxica diferente a la que conforma la matriz.Además, se han comparado los datos experimentales de las vigas de dovelas con los resultados obtenidos a partir de un modelo numérico desarrollado por Gonzalo Ramos, con el fin de visualizar los cambios de comportamiento de las vigas reforzadas con CFRP.Por último, se han redactado las conclusiones finales de la tesis, pudiéndose comprobar que éste tipo de materiales presentan importantes limitaciones para su aplicación y diseño como refuerzo de estructuras formadas por dovelas. Finalmente se proponen futuras líneas de investigación para dar continuidad a este trabajo de investigación. / The present Ph. D. Thesis is about the theoretical-experimental study of the behaviour of segmental bridges flexural strengthened by the technique of adhesion of Fiber Reinforcement Plastics (FRP). In order to accomplish this, a research program was developed in which 3 types of tests are included, characterization of materials, reduced models and structural level tests, using two kinds of systems of FRP reinforcement, besides the results obtained in the structural tests were compared with a numerical model.The tests corresponding to the experimental phase of this work have been made in the Laboratory of Structures Technology (LTE) of Superior Technical School of Civil Engineers of Barcelona (ETSECCPB) in the Technical University of Catalonia (UPC). These tests were divided in three main stages. They were made, in the first place, tests on segmental beams externally prestressed previously tested. They were reinforced using two different kind of systems of FRP reinforcement. Secondly, two series of adhesion tests were made in order to model the concrete segment joints and to know in detail the behavior of these systems of reinforcement in such structures. Finally, the reinforcement systems were characterized to compare the mechanical features provided by the manufacturers besides to corroborate the results obtained in the two first stages of the experimental phase of this work.In order make a base founded analysis of the experimental phase, a bibliographical revision on the state of the art has been made. It focuses to the history of application of the mentioned systems of reinforcement, applied to concrete structures, rendering special attention in the failure mechanisms, in specific to the peeling mechanism as well as to the adhesion of the FRP to the concrete, in which great part of this research is centered.On the other hand, the efficiency of the developed test of adhesion has been evaluated, with the intention of proposing it as tool for the characterization for these systems of reinforcement in the case of application to structures constituted by segments or in those in which construction meetings appear.With the purpose of demonstrating the validity of the adhesion test, two different reinforcement systems have been chosen. One constituted by carbon fiber bidirectional weave (TFC), with a relatively low elasticity modulus, in which the used epoxy resin for the adhesion of the FRP to the concrete forms the matrix of the same one, and a second system formed by prefabricated carbon fiber laminate (CFK), pre-impregnated with epoxy resin, with a elasticity modulus superior to first one, adhering it to the concrete with a different epoxy resin from which conforms the matrix.In addition, the experimental data of the segmental beams have been compared with the results obtained from a numerical model developed by Gonzalo Ramos, with the purpose of visualizing the changes of behaviour of the beams reinforced with CFRP.At last, the final conclusions of the thesis have been written up, allowing to verify that this particular type of materials presents important limitations for their application and design as reinforcement in segmental structures. Finally, future lines of investigation set out to give continuity to this research work.

Bond in a reinforced concrete (RC) structure is the interaction force that transfers force between the steel and concrete. It influences the structural performance and serviceability of a structure under both static and cyclic loading. Corrosion of reinforcing steel in RC structures is the primary reason behind bond loss in RC elements. A loss of bond in concrete results in a decrease in the serviceability strength and eventually causes a brittle and sudden failure. Structures, such as bridges, are vulnerable to corrosion and at the same time are subjected to repeated loading rather than static loading. Nevertheless, little experimental or analytical studies that address the problem of corroded steel-concrete bond under repeated loading exist. This study was aimed at increasing the understanding of the behaviour of bond between corroded reinforcing steel bars and concrete for structures subjected to repeated loading. In addition, the effect of fibre reinforced polymers (FRP) as a rehabilitation method was assessed. Fibre reinforced polymers is considered to be a state-of-the art rehabilitation material due to its advantages, such as high strength, light weight and ease of handling and application. Forty-seven anchorage-beam specimens were cast and tested. The specimens’ dimensions were 152 x 254 x 2000 mm reinforced with two 20M bars. The steel reinforcement in a specimen was unbonded except for 250 mm from each end. This bonded length was selected to ensure a bond failure. The corrosion was induced using an accelerated corrosion process. The parameters investigated were the corrosion level (0, 5 and 9% measured mass loss), whether the specimen was wrapped in the anchorage zone with a U-shaped carbon fibre reinforced polymer (CFRP) sheets or not, and the load range applied. The minimum load applied was 10% of the static bond capacity of the specimen. The maximum load was varied to give the desired range of fatigue lives (103 to 106 cycles). The test frequency for all repeated tests was 1.5 Hz. Results showed that the repeated loading either pushed the bottom concrete cover away from the steel bar by wedge action for unwrapped beams or cracked and crushed the CFRP confined bottom concrete cover for wrapped beams. The concrete damage caused the bond stress to undergo a gradual redistribution, moving the peak bond stress from the loaded end towards the free end, resulting in failure of the specimens by fatigue of bond. Corrosion levels of 5% and 9% decreased the fatigue bond strength on average by 19%. The rate of slip of the steel bar increased as the corrosion level increased. CFRP sheets changed the mechanism by which the concrete resist the bond forces by engaging the bottom cover. This in turn increased the fatigue bond strength at all corrosion levels on average by 31% compared to unwrapped specimens. Based on the test results and observations, a hypothesis of the mechanics of bond under repeated loading was postulated and a fatigue slip-growth analysis (similar to the fracture mechanics crack growth approach) was proposed to calculate the fatigue life of a specimen that fail in bond. The proposed analysis was in reasonable agreement with the experimental results.

Bond in a reinforced concrete (RC) structure is the interaction force that transfers force between the steel and concrete. It influences the structural performance and serviceability of a structure under both static and cyclic loading. Corrosion of reinforcing steel in RC structures is the primary reason behind bond loss in RC elements. A loss of bond in concrete results in a decrease in the serviceability strength and eventually causes a brittle and sudden failure. Structures, such as bridges, are vulnerable to corrosion and at the same time are subjected to repeated loading rather than static loading. Nevertheless, little experimental or analytical studies that address the problem of corroded steel-concrete bond under repeated loading exist. This study was aimed at increasing the understanding of the behaviour of bond between corroded reinforcing steel bars and concrete for structures subjected to repeated loading. In addition, the effect of fibre reinforced polymers (FRP) as a rehabilitation method was assessed. Fibre reinforced polymers is considered to be a state-of-the art rehabilitation material due to its advantages, such as high strength, light weight and ease of handling and application. Forty-seven anchorage-beam specimens were cast and tested. The specimens’ dimensions were 152 x 254 x 2000 mm reinforced with two 20M bars. The steel reinforcement in a specimen was unbonded except for 250 mm from each end. This bonded length was selected to ensure a bond failure. The corrosion was induced using an accelerated corrosion process. The parameters investigated were the corrosion level (0, 5 and 9% measured mass loss), whether the specimen was wrapped in the anchorage zone with a U-shaped carbon fibre reinforced polymer (CFRP) sheets or not, and the load range applied. The minimum load applied was 10% of the static bond capacity of the specimen. The maximum load was varied to give the desired range of fatigue lives (103 to 106 cycles). The test frequency for all repeated tests was 1.5 Hz. Results showed that the repeated loading either pushed the bottom concrete cover away from the steel bar by wedge action for unwrapped beams or cracked and crushed the CFRP confined bottom concrete cover for wrapped beams. The concrete damage caused the bond stress to undergo a gradual redistribution, moving the peak bond stress from the loaded end towards the free end, resulting in failure of the specimens by fatigue of bond. Corrosion levels of 5% and 9% decreased the fatigue bond strength on average by 19%. The rate of slip of the steel bar increased as the corrosion level increased. CFRP sheets changed the mechanism by which the concrete resist the bond forces by engaging the bottom cover. This in turn increased the fatigue bond strength at all corrosion levels on average by 31% compared to unwrapped specimens. Based on the test results and observations, a hypothesis of the mechanics of bond under repeated loading was postulated and a fatigue slip-growth analysis (similar to the fracture mechanics crack growth approach) was proposed to calculate the fatigue life of a specimen that fail in bond. The proposed analysis was in reasonable agreement with the experimental results.

Behavior of lap splices formed by CFRP rolls has been studied. CFRP rolls have been prepared by using CFRP sheets of a certain width. Strengthening methods that use CFRP rolls as reinforcement may require an epoxy anchored lap splice due to the conditions at the strengthening regions. It may not always be possible to strengthen the region by using only one roll fan anchored at both ends, but using two rolls from opposite faces of the member and lap splicing them at the middle so that they act as a single roll. Lap splice behavior can be studied best by using flexural beam bond specimens if the reinforcing material is steel. Therefore, it has initially been suggested that flexural beam specimens reinforced for flexure with CFRP rolls as tension reinforcement can be used in studying the lap splice behavior. However, due to the difficulties encountered in the beam tests, another type of test specimen was introduced, which was a direct pull-out specimen. In this type of test specimen, lap spliced CFRP rolls have been tested under direct tension, in which the tension has been applied by making use of concrete end blocks that transfer the tension to the rolls. Eleven tests have been made in total. Full material capacity of the rolls could not be achieved due to premature failures. However, important conclusions and recommendations have been made for future studies.

The use of fiber reinforced polymers (FRP's) for structural repair or retrofit has increased significantly in the last decade, with adoption for civil infrastructure occurring only in the last 20 years. These products are most often used to increase the capacity of damaged or deteriorated structures. Much research has been performed in the arena of testing of various FRP's bonded to both concrete and masonry substrates, the majority of which focusing on three areas; flexural strengthening, in-plane shear strengthening, and mechanical anchoring. Anchorage is commonly the limiting factor in the application of FRP's, due to the inability of the edge of the polymer matrix to reliably extend beyond a point of zero-interfacial stress. Where interfacial stresses exist and the FRP is terminated localized disbondment often occurs, these localized failures then propagate across the entire bond of the structural system. Various mechanical termination details have been tested to mitigate the potential failure modes near the ends of the fabric. There, however, has been very limited research performed on the behavior of dowels which are installed parallel to the FRP fabric and splayed onto the FRP fabric matrix. In this research the mechanical properties of carbon fiber reinforced polymer (CFRP) dowels with a parallel orientation to uniaxial carbon fabric are experimentally tested to determine the tensile capacity of "dowel to splay" CFRP connections and to discover any dominant failure modes.