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Prestressed hollow core slabs are essential components in structures such as bridges, parking garages, marine structures, and commercial and industrial buildings. Material degradation and altered functional requirements may seriously threaten the structural integrity of these reinforced concrete structures. Using FRP composites, the NSM strengthening technique presents a viable solution to these challenges. However, further investigation is required to establish comprehensive empirical design guidelines. The intent of this research project is to investigate the NSM technique in conjunction with common design concepts such as prestressed concrete, precast hollow core slabs, the complex behaviour of disturbed regions, and fiber-reinforced composite materials. An experimental program was developed, which included eleven full-scale slab specimens, subject to a four-point load configuration. The main parameters included the prestressing reinforcement ratio, CFRP strengthening ratio, and in-service opening location. Experimental results showed that prestressed concrete strengthened in flexure with NSM-CFRP is a viable technique for lower reinforcement ratios.

Στην παρούσα διατριβή διερευνήθηκε πειραματικά, η συμπεριφορά διατάξεων ενίσχυσης πλακοδοκών Οπλισμένου Σκυροδέματος, σε τέμνουσα, που αποτελούνται από το συνδυασμό τρίπλευρων μανδυών από Ινοπλισμένα Πολυμερή και αγκυρίων ινών. Πρόκειται για διατάξεις ενίσχυσης που λόγω της παρουσίας των αγκυρίων, καλούνται να υπερκεράσουν τις αδυναμίες της τεχνικής των «ανοικτών» μανδυών, δηλαδή της συνήθους τεχνικής ενίσχυσης πλακοδοκών σε τέμνουσα. Οι αδυναμίες της εν λόγω τεχνικής, οφείλονται στην ανεπαρκή αγκύρωση των άκρων του μανδύα. Η πειραματική διερεύνηση της συμπεριφοράς τέτοιων διατάξεων ενίσχυσης, έγινε με εφαρμογή τους σε τέσσερα δοκίμια πλακοδοκών Οπλισμένου Σκυροδέματος, και συγκρίθηκε με τη συμπεριφορά ενός δοκιμίου αναφοράς που δεν έφερε καμία διάταξη ενίσχυσης, καθώς και με τη συμπεριφορά ενός δοκιμίου ενισχυμένου μόνο με τρίπλευρο «ανοικτό» μανδύα ΙΟΠ, απουσία αγκυρίων. Όλα τα δοκίμια, υποβλήθηκαν σε μονοτονική φόρτιση μέσω συγκεντρωμένου φορτίου με φορά ώστε να προκαλείται θλίψη στο άνω πέλμα της δοκού, δηλαδή στην πλάκα, και οι συνθήκες στήριξης ήταν τέτοιες που να προσομοιώνουν αμφιέρειστη δοκό. Τα πρώτα Κεφάλαια της διατριβής αποτελούνται από την εισαγωγή, τη βιβλιογραφική ανασκόπηση και την περιγραφή της πειραματικής διαδικασίας. Στα επόμενα Κεφάλαια, πέραν της παρουσίασης των πειραματικών αποτελεσμάτων, επιχειρείται ο προσδιορισμός της αποδοτικότητας με παράλληλη προσέγγιση της συμπεριφοράς των διατάξεων ενίσχυσης με έμφαση στον τρόπο με τον οποίον τα αγκύρια την επηρεάζουν. Στο τελευταίο Κεφάλαιο παρουσιάζεται ο κεντρικός άξονας της διατριβής περιλαμβάνοντας και τη σύνοψη των συμπερασμάτων. / In the present thesis, the effectiveness of shear strengthening schemes for T-Shaped RC beams, consisting of FRP U-Jackets and FRP anchors, was experimentally investigated. For this purpose, six full-scale of T-Shaped RC beams were produced. One specimen served as reference (unstrengthened) beam, whereas the remaining five received FRP U-jackets; out of the latter FRP anchors were used in four beams in order to enhance the effectiveness of the strengthening schemes, whereas no anchoring system was applied to the fifth beam. All specimens were tested under monotonic loading causing compression to the wide part of the section. The first chapter of this dissertation discusses the necessity of strengthening beams in shear and introduce the objective of the study. A relatively extended literature overview about shear strengthening with externally bonded reinforcement is included in the second chapter. The purpose of the third chapter is to describe the way the specimens were designed and constructed. The strengthening procedure, the experimental setup and the materials’ properties are also included in this chapter. The test results are presented and discussed in the fourth chapter. In the fifth chapter calculations regarding the effectiveness of the strengthening schemes are presented, along with an attempt to understand their general behavior while emphasizing on the way the FRP anchors affect it. The final chapter includes the general conclusions of the present study.

To meet the economic, social and infrastructure needs of the community for safe and efficient transportation systems, long span bridges have been built throughout the world. Long span bridges are one of the most challenging kinds of structures in civil engineering. The cable-stayed bridges are of great interest mainly as an alternative and a more economic solution than the one of suspension bridges. In addition, the fiber reinforced polymer (FRP) composites are, nowadays, successfully used for constructing modern bridges, where the significant weight saving provides additional benefits. Because of the great flexibility, modern long-span cable-stayed bridges are usually very susceptible to dynamic loads especially to the earthquake and strong winds. Therefore, the earthquake-resistant and wind-resistant designs become one of key issues for successful construction of bridges. The objective of the present research is to develop a very efficient spline finite strip technique, for modelling and analysis of both conventional and hybrid FRP cable-stayed bridges. The study falls into the categories of bending, free vibration, seismic, and aerodynamic flutter analysis. The spline finite strip method (SFSM) is one of the most efficient numerical methods for structural analysis of bridges, reducing the time required for estimating the structural response without affecting the degree of accuracy. In the finite strip method, the degrees of freedom could be significantly reduced due to the semi-analytical nature of this method. However, the previous versions of SFSM are not able to model the entire bridge system. For that reason, the structural interactions between different structural components of the bridge could not be handled. In addition, the vibrations and displacements of the towers and cables could not be investigated. In the present formulation, all these obstacles have been eliminated. Moreover, the proposed finite strip technique is very efficient and accurate due to the drastic reduction in the formulation time, simplicity of data preparation, rapid rate convergence of the results, and the semi-analytical nature. Last but not least, and for the first time, a fully finite strip solution is extended to the area of wind engineering. Using the spline finite strip discretization, the aerodynamic stiffness and mass properties of the long-span cable-stayed bridge are derived. The aerodynamic properties along with the structural properties of long-span plates and bridges are formulated in the aerodynamic equation of motion and are used to analyze the flutter problem. The accuracy and efficiency of the proposed advanced finite strip method is verified against the finite element and field measurement results. The results demonstrate that this methodology and the associated computer code can accurately predict the dynamic and aerodynamic responses of the conventional and FRP long-span cable-stayed bridge systems. The outcome of the present research will lead to a comprehensive structural analysis of bridges in the framework of the proposed discretization which is more efficient and straightforward than the finite element analysis.

Este trabalho analisou o comportamento estrutural de polímeros reforçados com fibra de vidro - PRFV em elementos pré-moldados de concreto, com aplicações específicas em vigas de concreto. Realizou-se um estudo comparativo do comportamento de vigas pré-moldadas reforçadas com armadura convencional, segundo a norma brasileira NBR 6118:2003, e reforçadas com armadura de barras pultrudadas de PRFV, segundo o ACI 440.1R-06. O estudo visa obter subsídios para a aplicação de barras de reforço de PRFV, em relação ao Estado Limite de Serviço - ELS, em obras realizadas em regiões de alta agressividade ambiental. Posteriormente fez-se os mesmos modelos de cálculo em elementos finitos, onde foram comparados e analisados os resultados obtidos com o cálculo prescrito pelas normas. Nem todos os parâmetros da norma americana foram inseridos, uma vez que alguns coeficientes internos que contam com efeitos sísmicos e com a neve estão embutidos nos cálculos. Os resultados obtidos, principalmente no cisalhamento, foram altamente satisfatórios, validando a aplicação do PRFV nas vigas consideradas. / This work studied the behavior of precast beams when subjected to shear stress according to the brazilian standard NBR 6118:2003 reinforced with steel bar compared to the american standard ACI 440.1R-06 when the structural member was reinforced with glass fiber reinforced polymer - GFRP pultruded bars. The goal of this work is to acquire subsidies to apply the GFRP in aggressive environmental sites. Also the same model calculations were performed by using Finite Element Method and compared to the results of the calculation prescribed by the standards. Some parameters indicated in the ACI standard were not followed since they are related to seismic and snow effects. The obtained results mainly in shear loading were highly satisfactory which validates the use of GFRP in the considered beams.

Les présents travaux, à caractère numérico-expérimental, visent à approfondir la connaissance relative au comportement de murs maçonnés, principalement ceux renforcés par matériaux composites vis-à-vis de sollicitations dans leur plan (flexion composée). Ils s'inscrivent dans le cadre de la réhabilitation du patrimoine bâti vis-à-vis du risque sismique notamment du fait de la reconsidération du zonage en France rendu depuis peu plus exigeant. Aussi, d'un point de vue technologique, cette thèse vise à apprécier, évaluer et hiérarchiser l'intérêt et les potentialités de solutions de renforcement mobilisant des matériaux composites, à base polymère ainsi que des composites textile-mortier de nouvelle génération, couplés à des ancrages mécaniques ayant vocation à mieux valoriser ce type d'options. Deux échelles d'analyse ont été retenues dans le cadre de la partie expérimentale. A l'échelle du matériau, dans le but de caractériser finement les matériaux constitutifs de la maçonnerie de briques de béton creux et de générer des jeux de données aussi pertinents que fiables, notamment en prévision de la modélisation numérique, des essais de compression uni-axiale et de push-out à l'échelle « réduite » ont été conduits et ont permis de souligner, en accord avec la littérature, la nécessité de tenir compte de l'interaction brique-mortier, de consolider la compréhension des mécanismes d'endommagement et de rupture des éléments de maçonnerie tout en mettant en lumière l'importance relative des dispersions obtenues. A l'échelle du composant de structure, une campagne expérimentale de flexion composée portant sur six murs, dont un mur témoin, a été conduite sous sollicitations de flexion composée dans le plan des murs avec pour impératif la nécessité de restituer les conditions limites et de sollicitations sous séisme, tout en limitant le champ de l'étude au volet statique monotone en vue d'éprouver les solutions valorisées (matériaux composites et ancrage).Cette partie a permis, audelà de la mise en avant des bonnes dispositions en termes de capacité portante, d'une part, de caractériser comparativement le comportement de ces éléments tant à l'échelle globale (déplacement, capacité de déformation et de dissipation d'énergie, etc.) qu'à l'échelle locale (endommagement, déformations localisées, etc.) via une instrumentation judicieuse, et d'autre part de cerner l'importance des ancrages mécaniques vis-à-vis des sollicitations étudiées. L'approche numérique, de type éléments finis, a été mise à profit dans un deuxième temps pour tenter de restituer le comportement des murs (à l'échelle locale et globale). Sur la base d'une lecture bibliographique critique c'est l'approche micromécanique qui a eu nos faveurs. La modélisation a été conduite en trois dimensions (3D) à l'aide du logiciel ANSYS. Ainsi, les briques et le mortier sont modélisés indépendamment mais liés parfaitement. Deux variantes ont été proposées pour la modélisation de la maçonnerie saine et leur adéquation a été évaluée. Le premier modèle s'appuie sur un couplage entre le modèle de béton d'Ansys en traction et un comportement multilinéaire en compression pour modéliser le mortier, les briques sont supposées pourvues d'un comportement élasto-plastique bilinéaire pour lequel la résistance en compression de la brique est le seuil de la phase élastique. Dans le deuxième modèle, plus en phase avec les constats expérimentaux, seul le comportement des briques est modifié en introduisant un comportement post-pic adoucissant. En ce qui concerne la modélisation des murs renforcés par matériaux composites, ces derniers (FRP et TRC) ont été considérés comme parfaitement liés au substrat de maçonnerie. Toutefois, si le renfort de type FRP est modélisé par un comportement homogène orthotrope, le TRC, rarement modélisé jusqu'à lors, est simulé via deux approches (homogène et hétérogène) dans le but d'apprécier leur pertinence... / This study, using both experimental and numerical approaches, will help to better understand the behaviour of masonry walls. It especially focuses on walls reinforced with composite materials under in-plane loading conditions. In France, more stringent seismic design requirements for building structures have taken effect. So, this research has been initiated in an effort to define reliable strengthening techniques. The selected reinforcement materials are (1) – fiber reinforced polymer (FRP) strips using E-glass and carbon fabrics and (2) – an emerging cementbased matrix grid (CMG) system. The composite strips are mechanically anchored into the foundations of the walls to improve their efficiency. The experimental program involves different levels of analysis. Small-scale models of block masonry structures, carried out with less than ten bricks, are tested. The objective is to obtain a coherent set of data, characterizing the elementary components (hollow bricks and mortar) and their interface, in order to provide realistic values of the parameters required in the foreseen modelling. Shear bond strength has been obtained from triplets and 7-uplets and compressive masonry strength from running bond prisms. These experimental results improve the knowledge of the main damage mechanisms and failure modes of masonry but they suffer from high scattering. At laboratory (large) scale, six walls have been submitted to shear-compression tests - five of them are reinforced and the last one acts as a reference. All the walls share the same boundary and compressive loading conditions, which are chosen to ensure a representative simulation of a seismic solicitation. Nevertheless, masonry walls performances and anchor efficiency are only evaluated under monotonic lateral loadings. A comparative study on global behavior (displacements, deformation capacity, energy dissipation,…) as well as on local mechanisms (local strains, damage,…) is carried out and highlights in particular that strengthened walls exhibit a high increase in shear resistance. Moreover, a 3D finite-element analysis using ANSYS has been performed to help understand the behaviour of unreinforced and strengthened walls. A micro-mechanical approach is adopted: bricks and mortar are modelled separately and linked together by a perfect bond. The Ansys concrete model, capable of cracking, is coupled with a multi-linear plasticity model in compression to describe mortar joints. In a first attempt, bricks exhibit a bilinear behavior law where the brick compressive strength is the elastic threshold; but this model fails to reproduce the resistances of the strengthened walls. To compensate for these overestimations and capture the experimental resistances, a post-pic softening behaviour is preferred for the bricks. To model strengthened walls, all composite strips are supposed to be perfectly linked with the masonry and a linear elastic law is used for the FRP reinforcements. TRC strips are either described by means of a linear law or represented using a heterogeneous approach where matrix and textile grids are modelled separately. In this case, grids are represented using a smeared approach and are embedded within the matrix mesh. So, displacement compatibility is totally satisfied between the textile and the cementitious matrix. The proposed numerical model tends to underestimate walls capacity deformation but ultimate loads and failure modes are in coherence with experimental results. Finally, existing analytical methods have been applied to assess unreinforced and strengthened walls performances. The results are then compared with the experimental data and a critical review is proposed. Existing models could be refined by taking into account more realistic behaviour laws and by relying on energy approaches to better reproduce dissipative mechanisms of TRC materials

Ce travail concerne l’étude du renforcement de structures en pierres par matériaux composites. Deux techniques de renforcement sont utilisées. L’un s’agit de renforcement par matrice cimentaire renforcé avec de textile de fibre de verre TRC. L’autre est renforcement par barres de fibre de verre de FRP suivant la technique de NSM (near-surface mounted). La première phase consiste en la caractérisation des matériaux et l’analyse des comportements mécaniques en compression en cisaillement et en traction de petits éléments de maçonnerie composées d’un assemblage de pierre et mortier bâtard. Les valeurs caractéristiques du comportement mécanique de la maçonnerie sont comparées avec les différents modèles dans la littérature qui calculent les paramètres caractéristiques avec une bonne approximation avec les résultats expérimentales. En plus, le comportement de matériaux de renforcement sont testés en traction ainsi que le comportement de l’adhésion entre le renfort et la maçonnerie est étudié. La deuxième phase se concentre sur le renforcement de murs de maçonnerie soumis sur deux types de chargement. L’un s’agit de cisaillement dans le plan des murs effectué avec l’essai de compression diagonale. Le deuxième représente des charges de flexion à 3 points hors plan des murs accompagné par des forces de compression axiale qui provoque une contrainte de compression de 0.2 MPa. L’essai de cisaillement s’est réalisé sur des murs carrés de cinq rangées de pierres avec mortier. Le renforcement par deux barres verticales de NSM FRP améliore significativement la ductilité et le module de cisaillement des murs, ainsi que le renforcement avec deux couches orthogonales de TRC améliore la résistance au cisaillement. Enfin l’application de modèles analytiques a permet de comparer les résultats expérimentaux aux résultats donnés avec les modèles. En plus, l’essai de flexion à 3 points est effectué sur des murs composés de douze rangées de pierres avec mortier. Le renforcement avec deux barres verticales et deux barres transversales a plus augmenté la rigidité élastique. En revanche, le renforcement avec TRC composé d’une seule couche de textile accompagné avec une barre verticale de FRP n’augmente pas la résistance de mur par rapport à la résistance du mur renforcé avec une seule couche de textile ou avec une barre verticale seule / This work concerns the study of the reinforcement of stone structures with composite materials. Two reinforcing techniques are used. One is reinforcement by cement matrix reinforced with textile TRC of glass fiber. The other is by reinforcing FRP fiberglass rods according to NSM technique (near-surface mounted). The first phase consists of materials characterization and analysis of mechanical behavior in compression shear and tensile of small masonry specimens made of stone and mortar. The characteristic values of the mechanical behavior of the masonry are compared with the different models in the literature which calculate the characteristic parameters and give a good approximation with the experimental results. In addition, the behavior of reinforced materials is tested in tension and the behavior of the adhesion between the reinforcement and the masonry is studied. The second phase focuses on strengthening masonry walls subjected to two types of loading. One is in-plane shear of walls made with the diagonal compression test. Represents the second bending loads to 3 points out of plane walls accompanied by axial compression forces which cause a compressive stress of 0.2 MPa. The shear test was performed on square walls of five rows of stones with mortar. Strengthening by two vertical bars NSM FRP significantly improves the ductility and shear modulus of the walls and the reinforcement with two orthogonal layers TRC improves shear strength. Finally the application of analytical models used to compare the experimental results with the results given by the models. In addition, the bending test with 3-point is carried out on walls composed of twelve rows of stones with mortar. The reinforcement with two vertical bars and two crossbars increased more elastic stiffness. However, the reinforcement with TRC composed of a single layer of textile accompanied with a vertical bar FRP does not increase the resistance of the wall relative to the resistance of the reinforced wall with a single layer of textile or with a simple vertical bar

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<div> <p>Due to harsh environmental conditions, the deterioration of prestressed concrete bridge girders is a commonly observed phenomenon in Indiana and much of the Midwest. Concordantly, one widely observed damage scenario is deteriorated end regions of prestressed concrete girders. Damaged or failed expansion joints expose prestressed concrete girder end regions to chloride-laden water, resulting in a corrosive environment in which reinforcement section loss and concrete spalling can occur. For bridges experiencing this type of deterioration, action is needed to ensure the structure remains safe and serviceable. As such, an experimental program was developed to investigate the effectiveness of three repair techniques in restoring the structural behavior of prestressed concrete bridge girders with end region deterioration. The three examined repair techniques are (i) an externally bonded fiber reinforced polymer (FRP) system, (ii) a near-surface-mounted (NSM) FRP system, and (iii) a concrete supplemental diaphragm. Additionally, installation procedures for the three end region repair techniques were developed. Results, conclusions, and recommendations from the experimental program are presented to help advise best practices for implementing end region repair techniques in the field. </p> </div> <br>

Because FRP composites have high fiber strength and good durability, they are increasingly used for repairs, modernisation and reconstruction of concrete structures. In practice, however there is a risk of premature separation of FRP reinforcement from concrete. This can be avoided by appropriate selecting the fibers and the matrix and the appropriate shape of the reinforcement. The actual materials and consistency of FRP reinforcement with concrete are also covered by this diploma thesis.