Cette thèse s’inscrit dans le contexte d’une optimisation industrielle et économique des éléments de structure en BFUP permettant d’en garantir la ductilité au niveau structural, tout en ajustant la quantité de fibres et en optimisant le mode de fabrication. Le modèle développé décrit explicitement la participation du renfort fibré en traction au niveau local, en enchaînant une phase de comportement écrouissante suivie d'une phase adoucissante. La loi de comportement est fonction de la densité, de l'orientation des fibres vis-à-vis des directions principales de traction, de leur élancement et d'autres paramètres matériaux usuels liés aux fibres, à la matrice cimentaire et à leur interaction. L'orientation des fibres est prise en compte à partir d'une loi de probabilité normale à une ou deux variables permettant de reproduire n'importe quelle orientation obtenue à partir d’un calcul représentatif de la mise en œuvre du BFUP frais ou renseignée par analyse expérimentale sur prototype. Enfin, le modèle reproduit la fissuration des BFUP sur le principe des modèles de fissures diffuses et tournantes. La loi de comportement est intégrée au sein d'un logiciel de calcul de structure par éléments finis, permettant de l'utiliser comme un outil prédictif de la fiabilité et de la ductilité globale d’éléments en BFUP. Deux campagnes expérimentales ont été effectuées, une à l'Université Laval de Québec et l'autre à l'Ifsttar, Marne-la-Vallée. La première permet de valider la capacité du modèle à reproduire le comportement global sous des sollicitations typiques de traction et de flexion dans des éléments structurels simples pour lesquels l’orientation préférentielle des fibres a été renseignée par tomographie. La seconde campagne expérimentale démontre les capacités du modèle dans une démarche d’optimisation, pour la fabrication de plaques nervurées relativement complexes et présentant un intérêt industriel potentiel pour lesquels différentes modalités de fabrication et des BFUP plus ou moins fibrés ont été envisagés. Le contrôle de la répartition et de l’orientation des fibres a été réalisé à partir d'essais mécaniques sur prélèvements. Les prévisions du modèle ont été confrontées au comportement structurel global et à la ductilité mis en évidence expérimentalement. Le modèle a ainsi pu être qualifié vis-à-vis des méthodes analytiques usuelles de l'ingénierie, en prenant en compte la variabilité statistique. Des pistes d'amélioration et de complément de développement ont été identifiées / This Ph.D. project has been prepared within the context of an industrial and economic optimisation of UHPFRC structural elements to ensure ductility at the structural level, while adjusting the amount of fibre and optimising the manufacturing process. The model developed explicitly describes the participation of local fibre reinforcement in tension, thanks to a hardening behaviour followed by a softening one. The constitutive law is a function of the local fibre content, of the fibre orientation with respect to tensile principal directions, of the fibre slenderness and other usual material parameters related to the fibres, the cementitious matrix and their interaction. The fibre orientation is taken into account using a normal probability distribution with one or two variables to reproduce any orientation either obtained from a representative simulation of casting fresh UHPFRC or informed by experimental analysis on prototypes. Lastly, the model reproduces the cracking of UHPFRC based on the principle of smeared rotating crack models. The constitutive law is implemented in a structural finite element software as a predictive tool of reliability and overall ductility of UHPFRC elements. Two experimental campaigns were carried out, one at Laval University in Quebec and one at Ifsttar, Marne-la-Vallée. The first one is used to confirm the model ability to reproduce the overall behaviour under typical tensile and bending loads in simple structural elements for which the preferential fibre orientation was measured by microtomography. The second experimental campaign demonstrates the capabilities of the model, in an optimisation process, to help manufacture relatively complex ribbed triangular plates of industrial interest in which different manufacturing process and fibre volume have been considered. The identification of fibre distribution and orientation has been performed using mechanical tests on sawn samples. The model predictions have been compared to the global structural behaviour, and to the ductility demonstrated experimentally. The model could be qualified through comparison with conventional analytical engineering methods, taking into account the statistical variability. Improvement and additional developments have been identified

Nous nous intéressons dans ce travail à la mise en précontrainte par pré-tension d'éléments en Béton Fibré Ultra Performant (BFUP) par des renforts en Polymères Renforcés de Fibres de Carbone (PFRC). L'association de ces deux matériaux doit permettre de réaliser des éléments précontraints présentant une haute résistance mécanique et une grande durabilité. Cette étude à forte composante expérimentale s'est déroulée en trois phases. La première phase concerne l'étude de l'adhérence entre les PFRC et le BFUP au cours de laquelle des configurations de surface optimales des renforts (joncs) sont présentées. Dans la deuxième phase nous proposons un système d'ancrage permettant de mettre en tension les joncs de précontrainte. Ce système permet de conserver l'intégralité de la résistance en traction des joncs PFRC. La troisième phase est dédiée à une campagne expérimentale d'essais de flexion 4 points menée sur des poutres BFUP précontraintes par des joncs PFRC et des torons acier. Le comportement global des poutres précontraintes en flexion est analysé en termes de rigidité, de suivi de la fissuration, de pertes de la précontrainte, de capacité portante et de ductilité. Les résultats obtenus sont très encourageants et ouvrent des perspectives pour l'utilisation des PRFC en tant que renforts actifs pour la précontrainte / We are interested at this work in the prestressing by pre-tensioning of Ultra High-Performance Fibre Reinforced Concrete (UHPFRC) with Carbon Fibre Reinforced Polymer bars (CFRP). The combination of these two materials should allow to produce prestressed members with high strength and durability. This intensive experimental study was conducted in three phases. The first phase involves the study of bond between the PFRC and UHPC at which the optimal configurations of surface reinforcements (rods) are presented. In the second phase we propose an anchoring system for pretensioning of CFRP bars. This system keeps all of the tensile strength of PFRC bars. The third phase is devoted to an experimental campaign of 4 points bending tests conducted on UHPC beams prestressed by CFRP bars and steel strands. The overall behavior of prestressed beams in bending is analyzed in terms of stiffness, followed by cracking, loss of prestresse, bearing capacity and ductility. The results are very encouraging and open up prospects for the use of CFRP as reinforcement for prestressing

When compared to traditional concrete, steel fibre reinforced concrete (SFRC) shows several enhancements in performance, including improved tensile resistance, toughness and ductility. One potential application for SFRC is in columns where the provision of steel fibres can improve performance under axial and lateral loads. The use of SFRC can also allow for partial replacement of transverse reinforcement required by modern seismic codes. To improve workability, self-consolidating concrete (SCC) can be combined with steel fibres, leading to highly workable SFRC suitable for structural applications. Recent advances in material science have also led to the development of ultra-high performance fibre reinforced concretes (UHPFRC), a material which exhibits very high compressive strength, enhanced post-cracking resistance and high damage tolerance. In heavily loaded ground-story columns, the use of UHPFRC can allow for reduced column sections. This thesis presents the results from a comprehensive research program conducted to study the axial behaviour of columns constructed with highly workable SFRC and UHPFRC. As part of the experimental program, twenty-three full-scale columns were tested under pure axial compressive loading. In the case of the SFRC columns, columns having rectangular section and constructed with SCC and steel fibres were tested, with variables including fibre content and spacing of transverse reinforcement. The results confirm that use of fibres results in improved column behaviour due to enhancements in core confinement and cover behaviour. Furthermore, the results demonstrate that the provision of steel fibres in columns can allow for partial replacement of transverse reinforcement required by modern codes. The analytical investigation indicates that confinement models proposed by other researchers for traditional RC and SFRC can predict the response of columns constructed with SCC and highly workable SFRC. In the case of the UHPFRC columns, variables included configuration and spacing of transverse reinforcement. The results demonstrate that the use of appropriate detailing in UHPFRC columns can result in suitable ductility. Furthermore, the results demonstrate the improved damage tolerance of UHPFRC when compared to traditional high-strength concrete. The analytical investigation demonstrates the need for development of confinement models specific for UHPFRC.

Das Institut für Tragwerksentwurf (ITE) und das Institut für Baustof e, Massivbau und Brandschutz (iBMB) der TU Braunschweig bearbeiteten in der ersten Förderperiode des SPP 1542 „Leicht Bauen mit Beton“ gemeinsam das Teilprojekt „Entwicklung neuartiger Verbindungen für geometrisch komplexe Flächen- und Stabwerkselemente aus UHPC“. Schwerpunkt waren umfangreiche Untersuchungen zu geometrisch komplexen und hochpräzise hergestellte trocken gefügten Stoßverbindungen für dünnwandige UHPC-Bauteile zur Übertragung von Druck-, Biege- und Scherkräften. Zur Verbesserung der Zugtragfähigkeit und des Nachbruchverhaltens wurde im Forschungsprojekt stahlfaserverstärkter ultrahochfester Beton (UHPFRC) verwendet. Die einzelnen Arbeitspakete waren entsprechend der Expertisen der beiden Institute aufgeteilt. Während sich das ITE insbesondere mit der Entwicklung der Bauteil- und Fugengeometrien sowie dem Schalungsbaus befasste, lagen Planung und Umsetzung der experimentellen und numerischen Material- und Bauteiluntersuchungen in der Verantwortung des iBMB. [Aus. Einleitung) / The Institute of Structural Design (ITE) and the Institute of Building Materials, Concrete Structures and Fire Safety (iBMB) of the Technical University of Braunschweig worked together in the f rst funding period of the SPP 1542 “Concrete Light” on the subproject “Development of novel jointing systems for complex beam surface and spatial elements made of UHPFRC”. The focus was on extensive investigations of geometrically complex and high-precision dry-jointed connections for thin-walled UHPC components for the transmission of compressive, bending and shear forces. Steel f bre reinforced ultra-high performance concrete (UHPFRC) was used in the research project to improve the tensile strength and post fracture behaviour. The individual work packages were divided according to the expertise of the two institutes. While the ITE was particularly concerned with the development of the component and joint geometries as well as the formwork construction, the iBMB was responsible for the planning and implementation of the experimental and numerical material and element analyses. [Off: Introduction]

Ce travail de recherche vise à évaluer le comportement au fluage de nouvelles structures composites en associant trois matériaux: le bois, le béton fibré ultra-haute performance (BFUP) et des armatures polymères renforcées de fibres de carbone (PRFC). Le but de la conception d'une telle section hybride est de faire usage des meilleures caractéristiques de chaque matériau afin d'augmenter sa capacité portante à l'ultime et/ou en service. Aussi, d'un point de vue du comportement mécanique, cette solution de renforcement vise à apprécier et hiérarchiser l'intérêt d'une telle solution liée aux effets déférés, particulièrement au fluage. La première étape consiste à mener une analyse expérimentale sur le comportement en statique de poutres hétérogènes bois-BFUP. Elle est exécutée afin de mieux comprendre le mécanisme d'endommagement ainsi que la performance pour définir le comportement au fluage. Pour cela, une campagne expérimentale en flexion quatre points portant sur trois poutres, dont une poutre témoin, a été conduite sous sollicitation statique. Les résultats obtenus confirment que les poutres hétérogènes Bois-BFUP apportent une optimisation de capacité portante ainsi que de la rigidité. Les poutres hybrides ont permis d'obtenir le même mode de rupture en flexion et la première rupture s'est produite dans la partie comprimée de BFUP supérieur. La seconde partie de la recherche est consacrée à l'analyse du comportement au fluage de poutres hétérogènes bois-BFUP nécessaire pour prédire les déformations à long terme dans des structures composites hybrides. Dans cette étude, deux types d'essai ont été réalisés : essai en environnement contrôlé et essai en environnement non contrôlé (extérieur). En environnement contrôlé les essais fluage ont commencé sous une charge constante de 24 kN dans le laboratoire avec des températures de 20±5 °C et une humidité relative entre 40% et 60%. Ces conditions climatiques peuvent être considérées comme un environnement de classe 1, conformément à l'Eurocode 5. Les résultats ont montré que la flèche de fluage de la poutre renforcée augmente peu tout au long de l'essai. A l'inverse de ces résultats, l'essai de fluage en environnement variable à l'extérieur du laboratoire, qui peut être considéré comme environnement de classe 3 suivant l'Eurocode 5, montre que les effets différés du bois et du béton jouent un rôle très important dans l'évolution de la flèche finale / This dissertation aims to evaluate the creep behaviour of a new composite structure combined three materials: the wood, the ultra-high performance fibre-reinforced concrete (UHPFRC) and the polymer fibre reinforced carbon (CFRP) according to their advantages and performances. The conception of such hybrid section is to use the best characteristics of each material to increase its bearing capacity in the ultimate and / or in service. Furthermore, from the point of view of design, this strengthening solution is to assess and prioritize the interests to reduce the deformation caused by the delayed effects, particularly caused by creep. The first part investigated an experimental analysis of the static behaviour of the wood-UHPFRC beam, and should be performed to understand the mechanism of the hybrid beam as well as the performance which are the directions to identify the creep behaviour. A four-points bending test setup on three beams, one beam witness, was conducted under static loading. The results confirm that heterogeneous Timber-UHPFRC beams provide an optimization of bearing capacity and stiffness. The hybrid beams have produced the same flexural mode of failure and the first crack occurred in the upper part of compressed UHPFRC. The second part of the research is devoted to the analysis of creep behaviour of heterogeneous wood beams UHPC necessary to predict long-term deformations in composite structures. In this study, two types of test setups were conducted: test in a sheltered and outdoor environment. In the sheltered environment, the creep test began under a constant load of 24 kN in the laboratory with temperatures of 20 ± 5 °C and a relative humidity between 40% and 60%. These climatic conditions can be considered as the service class 1, according to Eurocode 5. The results showed that the creep deflection of the reinforced beam gradually increases throughout the test. Unlike these results, the creep test in a variable environment outside the laboratory, which can be considered Class Service 3 to Eurocode 5, shows that the effect of time dependency behaviour of wood and concrete plays a very important role in the evolution of the creep deflection of the hybrid beams

Ultra high performance fibre reinforced concrete (UHPFRC) is a relatively new fibre reinforced cementitious composite and has become very popular in construction applications. Extensive experimental studies have been conducted, demonstrating its superior properties such as much higher strength, ductility and durability than conventional fibre reinforced concrete (FRC) and high performance concrete. However, the material's damage and fracture mechanisms at meso/micro scales are not well understood, limiting its wider applications considerably. This study aims at an in-depth understanding of the damage and fracture mechanisms of UHPFRC, combining microscale in-situ X-ray computed tomography (µXCT) experiments and mesoscale image-based numerical modelling. Firstly, in-situ µXCT tests of small-sized UHPFRC specimens under wedge splitting loading were carried out, probably for the first time in the world, using an in-house designed loading rig. With a voxel resolution of 16.9µm, the complicated fracture mechanisms are clearly visualised and characterised using both 2D images and 3D volumes at progressive loading stages, such as initiating of micro-cracks, arresting of cracks by fibres, bending and pulling out of fibres and spalling of mortar at the exit points of inclined fibres. Secondly, based on the statistics of pores in the µXCT images obtained for a 20mm cube specimen, an efficient two-scale analytical-numerical homogenisation method was developed to predict the effective elastic properties of the UHPFRC. The large number of small pores were first homogenised at microscale with sand and cement paste, using elastic moduli from micro-indentation tests. 3D mesoscale finite element models were built at the second scale by direct conversion of the µXCT images, with fibres and large pores were faithfully represented. The effects of the volume fraction and the orientation of steel fibres on the elastic modulus were investigated, indicating that this method can be used to optimise the material micro-structure. Thirdly, 3D mesoscale finite element models were built for the specimen used in the in-situ µXCT wedge splitting test, with embedded fibre elements directly converted from the µXCT images. The fracture behaviour in the mortar was simulated by the damage plasticity model available in ABAQUS. Finally, 2D mesoscale finite element models were developed to simulate the fracture behaviour of UHPFRC using cohesive interface elements to simulate cracks in the mortar, and randomly distributed two-noded 1D fibres and connector elements to simulate the pull-out behaviour of fibres. This approach offers a link between the fibres pull-out behaviour and the response of the whole composite at the macroscale, thus it can be used to conduct parametric studies to optimise the material properties.

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

Les travaux présentés sont une contribution à l’état des connaissances sur les déformations différées des Bétons Fibrés à Ultra hautes Performances (BFUP) subissant un traitement thermique réalisé à température modérée. Ce type de traitement thermique est appliqué dans des conditions de fabrication usine, juste après la mise en œuvre du béton dans son moule, en vue d’accélérer pendant quelques heures le durcissement d’un produit destiné à se voir appliquer une précontrainte au jeune âge. L’analyse bibliographique souligne l’importance de considérer le type de traitement thermique utilisé comme un des paramètres prépondérants associés à la structuration des hydrates à court, moyen et long terme et à la teneur en eau résiduelle libre des bétons. Les résultats expérimentaux ont permis d’une part de quantifier les déformations différées de BFUP subissant un traitement thermique à température modérée et d’autre part de mettre en corrélation ces déformations avec l’évolution de paramètres matériaux mesurés tels que l’humidité relative interne et le degré d’hydratation. Des modèles analytiques adaptés, s’inspirant de ceux présentés dans l’Eurocode 2, sont proposés pour prévoir les déformations différées des BFUP. En outre, la modélisation et les simulations numériques révèlent qu’il est possible de prédire correctement le comportement de ces BFUP tant sur l’évolution des températures internes que sur l’évolution des déformations différées. La prédiction de l’évolution des propriétés des produits en BFUP en fonction de la nature de l’échauffement appliqué devrait permettre en outre l’optimisation des cadences de production et de l’énergie utilisée pour les traitements thermiques. / The work presented is a contribution for the state of knowledge on the time-dependent strains of Ultra-High Performance Fiber-Reinforced Concrete (UHPFRC) subjected to a heat treatment at a moderate temperature. This type of heat treatment is applied under factory’s conditions, just after the placement of the concrete in its mould, in order to accelerate during a few hours the hardening of an intended product to be seen applying a prestressing to the early age. The bibliographical analysis gives the importance to consider the type of heat treatment used as a significant parameter associated to the hydrates’ structure with short, medium and long term and to the free residual water content of the concretes. The experimental results made it possible on the one hand to quantify the time-dependent strains of UHPFRC subjected to a heat treatment at a moderate temperature and on the other hand to correlate these strains with the evolution of material parameters measured such as the internal relative humidity and the degree of hydration. Adapted analytical models, taking as a starting point those presented in Eurocode 2, are proposed to consider the time-dependent strains of UHPFRC. Moreover, modeling and simulations reveal that it is possible to predict correctly the behavior of these UHPFRC as well on the change of internal temperatures as on the change of the time-dependent strains. The prediction of the evolution of the properties of the UHPFRC products according to the nature of the heating applied should allow moreover the optimization of the production cadences and the energy used for the heat treatments.

Die Vision bei diesem Projekt bestand darin, zukünftig anstelle massiver Betontragsysteme mit meist ungleichmäßiger Materialausnutzung am Kraftfluss orientierte, filigrane, stabartige Tragwerke zu entwerfen, die sich neben der Gewichtsreduktion und einer höheren Transparenz auch durch eine bessere Ressourcennutzung auszeichnen. Dabei wurde eine modulare Bauweise angestrebt, bei der die Einzelkomponenten Druckstab und vorgespannter Zugstab sowie Teile des Verbindungsknotenelements vorgefertigt und am Einsatzort zusammengefügt werden. Sowohl im Hinblick auf die Tragfähigkeits- und Verbundeigenschaften als auch auf die Dauerhaftigkeit sollten die Stäbe aus faserverstärktem Ultrahochleistungsbeton (UHPFRC) hergestellt sowie ausschließlich mit nichtmetallischen Elementen aus faserverstärkten Kunststoffen (FVK) bewehrt bzw. vorgespannt werden. Im geförderten Zeitraum lag das Hauptaugenmerk auf der Entwicklung filigraner, formoptimierter Druck- und vorgespannter Zugstäbe. Zum Knotenelement wurden theoretische Überlegungen sowie erste Tastversuche angestellt. [Aus: Projektidee und Zielsetzung] / The vision of this project was to replace massive concrete structures with mostly inhomogeneous material utilization in the future by designing filigree concrete truss supporting structures in accordance with the principle form follows force instead. Thus, besides weight reduction and a higher transparency also a higher resource efficiency can be achieved. A modular construction method, in which the components compression strut, prestressed tie and connection joint elements are prefabricated and joined together at the construction site, was aspired. With regard to load-bearing capacity and bonding behaviour as well as durability, the struts and ties are made of Ultra-High Performance Fibre-Reinforced Concrete (UHPFRC) and are reinforced or prestressed exclusively with non-metallic elements made of f bre-reinforced polymers (FRP). Within the funding period, the focus was on the development of f ligree, shape-optimized struts and prestressed ties. Regarding the connection joint element, theoretical considerations were made and first basic tests were carried out. [Off: Vision and objective]

O trabalho dedica-se ao estudo das torres eólicas protendidas de concreto, com a finalidade de promover a discussão sobre os critérios de dimensionamento, tema de grande relevância na atualidade. Para tal, foi considerada uma torre eólica de 100 m de altura provida de turbina de 5 MW, cujas ações foram obtidas da literatura. O carregamento de vento ao longo da torre foi tratado como estático equivalente de acordo com disposições normativas, através de uma forma simplificada para a adoção de uma velocidade de projeto equivalente à incidente no rotor. Com base na literatura, apenas as condições mais críticas foram adotadas no dimensionamento. As combinações entre os carregamentos e os coeficientes parciais de segurança foram delineados a partir do método dos estados limites, o qual se encontra amplamente difundido em normas de projeto. Os esforços e deslocamentos na torre foram obtidos pelo método dos elementos finitos com discretização em elementos finitos unidimensionais, considerando as não linearidades física e geométrica por intermédio do acoplamento de um programa comercial de elementos finitos com algoritmo desenvolvido em linguagem MATLAB, que tanto define as diversas geometrias de cada elemento ao longo da torre (seção variável), como obtém para cada um: a armadura ativa longitudinal a partir de perdas de protensão recalculadas, o diagrama momento-curvatura-força normal, e a armadura passiva longitudinal escalonada, que é otimizada durante o processo do dimensionamento. Quanto à resistência ao esforço cortante das seções anulares, foi proposto um modelo que apresentou boa concordância com os resultados experimentais obtidos na literatura. Além dos concretos convencionais, é discutido o estado-da-arte do concreto de ultra-alto desempenho reforçado com fibras, CUADRF, tratando sobre seu desenvolvimento histórico, composição, diferentes tipos, propriedades mecânicas, aplicações, recomendações para projeto e as simplificações adotadas quanto ao seu uso nas torres eólicas. Ao final foram realizadas análises paramétricas relativas à geometria e à classe de concreto para dois tipos de torres: em tronco de cone e de variação parabólica. Uma das principais conclusões do trabalho é que a otimização da área de aço passivo ocorre de forma sistemática para as torres de frequência natural mais baixa, tornando indispensável o uso de um modelo não linear para o correto dimensionamento. Além disso, as torres obtidas foram comparadas através do custo material total, constatando-se que as torres mais econômicas possuíam variação parabólica. Isso permitiu aferir um valor inicial para o qual o uso do CUADRF em torres eólicas passaria a ser competitivo. / The work is dedicated to the study of prestressed wind towers of concrete, in order to promote discussion on the design criteria, highly relevant topic today. For this purpose, it was considered a wind tower 100 m high provided with 5 MW turbine, whose actions were obtained from the literature. The wind loading along the tower was treated as static equivalent in accordance with design codes, through a simplified way for the adoption of a design speed equivalent to that incident on the rotor. Based on the literature, only the most critical conditions were adopted in the design. The combinations between loads and partial safety factors were outlined by the limit states method, which is widespread in design standards. The forces and displacements in the tower were obtained by the finite element method with discretization in frame elements, through material and geometric nonlinearities. This was done through coupling of a commercial finite element program with algorithm developed in MATLAB language, which defines both the various geometries of each element along the tower (variable section), and obtains for each: prestressing reinforcement from recalculated prestressing losses, the moment-curvature-normal diagram, and the stepped longitudinal passive reinforcement that is optimized during the design process. For the shear strength of the annular sections, a model that showed good agreement with the experimental results obtained in the literature was proposed. In addition to conventional concrete, the state-of-the art of ultra-high performance fiber reinforced concrete, UHPFRC, is discussed, dealing on its historical development, composition, different types, mechanical properties, applications, recommendations for design and simplifications adopted on its use in wind towers. At the end were performed parametric analyzes of the geometry and the concrete class for two types of towers: frustoconical and with parabolic variation. One of the main conclusions is that the optimization of passive steel area occurs systematically to the lower natural frequency towers, making it essential to use a nonlinear model for proper design. Moreover, the towers obtained were compared with the total material cost, having noticed that most economical towers had parabolic variation for the constraints here imposed. This allowed the assessment of an initial value for which the use of UHPFRC in wind turbine towers would be competitive.