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El present treball és un anàlisi i diagnòstic de l'estructura mòbil de la Villa Girasole, edifici singular en formigó armat que fou construït en 1935 per l'enginyer civil Angelo Invernizzi a Marcellise, Verona. La principal característica d'aquest edifici resideix en la seva mobilitat: en efecte, sobre una part fixa, l'estructura principal és capaç; de girar 360 graus per orientar-se cap el sol. Una altre característica remarcable és la seva magnitud, amb més de 42 metres d'alçada i 23 d'amplada la part mòbil té un pes de 1500 T. Per tal de donar mobilitat a l'estructura, l'enginyer la construeix sobre rails i la fa girar gràcies a dos rodets motoritzats. Després la mort de l'enginyer en 1958, la Villa Girasole va quedant poc a poc deteriorada i la seva mobilitat reduïda. Actualment, gràcies a la col·laboració entre la filla de l'enginyer i l'Accademia di architettura di Mendrisio s'ha creat una fundació amb l'objectiu de recuperar i tornar a fer girar aquesta meravella de l'arquitectura. Mitjançant aquest treball es pretén analitzar l'estructura mòbil i determinar la seva conformitat segons la norma suïssa actual, SIA 2003. La motivació ve donada degut a una primera inspecció que determina en bon estat els mecanismes de rotació però assenyala problemes de cimentació com els responsables de l'aturada de la part mòbil de l'estructura. L'estudi comença amb un resum històric de la bibliografia dels autors del projecte per situar-nos dins del context. Seguidament, es compara la Villa Girasole amb la resta d'edificis giratoris existents per veure'n l'evolució i el futur d'aquestes. A continuació, el treball es centra únicament en l’anàlisi estructural de la part mòbil de la Villa Girasole. Gràcies a la recopilació de la informació existent de l'edifici i a la visita del mateix es crea un model estàtic global de l'estructura. EI primer anàlisi realitzat és a l'Estat Límit Últim utilitzant diferents models reduïts per determinar les sol·licitacions. La seguretat a flexió composta i a l’esforç tallant són verificades presentant un bon marge de seguretat. Posteriorment es realitza un anàlisi a l'Estat Límit de Servei de l'estructura. De la mateixa manera, l'estructura en servei és verificada admetent una deformació abans de la creació de la primera ròtula plàstica. Dins de l'anàlisi en servei, el següent pas ha sigut tenir en compte la deformació actual de l'estructura, mesurada in situ el dia de la visita. Els resultats per aquest anàlisi demostren que la part mòbil pot suportar la deformació actual de l'estructura sense arribar a la creació d'una ròtula plàstica. Finalment, un estudi de l'estabilitat estructural, tenint en compte la deformació estructural de l'estructura, és realitzat. El resultat elimina el pandeig com a possible causa de ruïna de l'estructura. Les conclusions de l'estudi a l'Estat Límit Últim remarquen un bon marge de seguretat de l'estructura segons la norma suïssa SIA 2003. De l'estudi a l'Estat Límit de Servei, el resultats demostren com l'estructura mòbil pot suportar les deformacions actuals i per tant la rotació de la mateixa. Finalment, es senyala l'anell de suport horitzontal de la part mòbil com el punt clau pel control de les deformacions i es fa atenció als elements ornamentals com a crítics per suportar les deformacions imposades.

The present research improves the experimental and theoretical knowledge on the behaviour of structural elements made of ultra high performance fibre reinforced concrete (UHPFRC) with ordinary reinforcement. UHPFRC is a recently developed material with much higher mechanical properties and durability than ordinary concrete. However, it has been used so far in a limited number of structural applications. A better knowledge on the behaviour of UHPFRC in structural members is needed to be able to take advantage of its outstanding properties in structural design. One of the ways in which the structural efficiency of UHPFRC can be studied is to investigate the improvement in structural performance that is gained by using UHPFRC instead of ordinary concrete in common structural members. As an alternative, new structural shapes and structural concepts can be explored, more adapted to the specific material properties. The work presented in this thesis focuses on the first approach by considering the behaviour and modelling of UHPFRC structural members loaded in tension and in bending with axial load, and reinforced with ordinary steel reinforcement. The experimental and theoretical study carried out on tensile members contributes to the understanding of the fundamental mechanisms that control cracking of a tensile member reinforced with both fibres and bars, in service and at ultimate. A numerical model has been developed to solve the differential problem of bond in the presence of strong mechanical non linearity. This model has been used to simulate the main aspects controlling bond in a UHPFRC member. The results obtained with the model help in clarifying the differences between cracking in ordinary concrete and in UHPFRC ties. The model allows identifying the parameters that influence the strength and ductility of the tie and was used to validate simplified assumptions to model the behaviour of UHPFRC ties in service. The behaviour of columns has been studied with a theoretical and experimental approach. The results of two test series on UHPFRC and HPFRC columns are reported in the thesis. An analytical model has been developed to study the behaviour of a confined concrete member in compression. A numerical model has been implemented to simulate the non linear behaviour of ordinary concrete and UHPFRC columns. The models have been used to simulate test results reported in this thesis or taken from the literature. The numerical model has been used to evaluate the effect of variations of the mechanical behaviour of concrete on the structural behaviour of a column, with or without reinforcement. The results of those parametrical studies help understanding the influence of mechanical properties on structural response. This thesis contributes to a better understanding of the behaviour of UHPFRC members with ordinary reinforcement. The comparative approach used in the research makes it possible to show the differences between the structural behaviour of ordinary, high strength and fibre reinforced concrete. Indications are also given on the possible ways in which an effective use of UHPFRC in structural members can be achieved.

Reinforced concrete bridge deck slabs without shear reinforcement can be subjected to concentrated or distributed loads of important magnitude. Under these loads their structural response is not always ductile. In particular under concentrated loads their deformation capacity can be limited by shear or punching shear failures, which prevent them from reaching the ultimate load predicted by pure flexural analysis. This problem has been studied in this research by means of an important experimental program and theoretical modeling. The limited ductility of bridge decks was investigated by means of full scale tests on bridge deck cantilevers under groups of concentrated loads. Six large scale laboratory tests were performed on two bridge deck cantilevers with a span of 2.8 m and a length of 10.0 m. All slabs failed in a brittle manner, in shear or punching shear. The theoretical flexural failure load estimated using the yield-line method was never attained. Despite the brittle failures, the results of tests on cantilevers have shown that some amount of yielding can occur before the shear failure and therefore reduce the shear strength. This effect was quantified on eleven full scale tests on slab strips without shear reinforcement with a length of 8.4 m. The results clearly show that the increase of plastic strains in the flexural reinforcement leads to a reduction of the shear strength. The measured rotation capacity of the plastic hinge was thus limited by a shear failure. A particular problem of bridge deck slabs is the introduction of concentrated loads applied by wheels with pneumatic pressure. Punching shear with these loads is usually treated in a manner similar to punching by a column. A punching shear test was performed with a concentrated load simulating a vehicle wheel with pneumatic pressure to investigate the differences. It appears that punching shear with a wheel with pneumatic pressure is less critical because curvatures tend to be distributed over the surface of the applied load rather than concentrated near the edges of the column. In order to investigate the experimental results on slab strips without shear reinforcement, a mechanical model is proposed to predict the shear strength and rotation capacity of plastic hinges. The shear strength is formulated as a function of the opening of the shear crack and of the strength of the concrete compression zone. The results of the mechanical model are in good agreement with the measured values, both for the shear strength and for the shear carried across the shear crack. Based on the mechanical model, a simplified equation is proposed. The model can also be used to predict the shear capacity of yield-lines. A non linear finite element model was implemented during this work and used to correctly predict the measured rotations and load-displacements curves of the tested cantilevers and other full scale tests performed by other researchers. The measured failure loads are accurately estimated by using the results of the non-linear model and the one-way shear and punching shear criteria proposed by Prof. A. Muttoni (Muttoni 2003).

Ultra-High Performance Fiber-Reinforced Concrete (UHPFRC) can be considered, due to its high strength and improved durability, as one of the leading recent innovations in civil engineering. Material scientists have developed a very efficient, high-tech material by optimizing the concrete composition and improving the density of the cement matrix. Its structural behavior and in particular its relatively high ductility, despite the brittle behavior of the cement matrix, is influenced significantly by the crack-bridging behavior of the fibers. This behavior affects not only the tensile behavior, but also the global material behavior, i.e.: bending (tension by bending), compression (transversal tension, confinement), shear, punching, concentrated load introduction, etc. In the presented study, the tensile behavior of UHPFRC is analyzed as a basis for its structural behavior. The investigations extend from the 'micro-scale' behavior of the crack-bridging fibers in one crack to the 'macro-scale' behavior of tension members composed of UHPFRC. To obtain efficient tensile performance, the use of the UHPFRC in combination with reinforcing bars is expedient. The bond between the reinforcing bars and the UHPFRC is investigated, in order to analyze and understand the structural response of reinforced UHPFRC tension members. At each level of investigation, emphasis is placed on comprehension of the mechanical process. The influence of the fiber orientation, creep, shrinkage, and pre-stressing is discussed. Based on the studied mechanical processes, micro- and macro-scale modeling of the structural behavior is carried out. The cracking mechanisms of UHPFRC are examined in the research work. For the structural response of reinforced UHPFRC tension members, the influence of the double multi-cracking behavior is particularly relevant. First, multiple meso-cracks form controlled by the fibers and then multiple macro-cracks form controlled by the bond between the UHPFRC and the reinforcing steel. With a model based on these mechanisms, the structural response of tension members made from different types of UHPFRC can be described. Depending on the configuration of the tension member (i.e.: type of UHPFRC, reinforcement ratio, steel type, pre-stressing), five different failure regimes result for reinforced UHPFRC tension members. For practical applications the following conclusions can be drawn: Tension members composed of UHPFRC show very efficient structural behavior. The resistance of the UHPFRC supplements the steel resistance according to its strain-respective cracking state. The well distributed cracking of the UHPFRC leads to a considerable increase in the rigidity of the tension member (high tension stiffening effect). To obtain an efficient tension member with a large deformation capacity, a relatively high reinforcement ratio is necessary. Due to the associated continuous hardening behavior and significant elastic deformation, the use of high-strength reinforcing steel without a yielding plateau is favorable.

Punching of reinforced concrete and prestressed slabs is usually a critical failure mode for the design and verification of structures such as flat slabs or bridge slabs. Although codes of practice propose several rules for common cases (usually with an empirical basis), they do not provide a general tool for studying the punching strength because they are not based on a physical model. Furthermore, a better accuracy in the determination of the punching strength is needed when investigating the ultimate load of existing structures. Recently, test results from a series of 10 concrete slabs without punching reinforcement (performed within this thesis) as well as different tests performed by other researchers allowed to check and validate the application limits of a failure criterion proposed by Professor Muttoni for slabs without punching reinforcement. This failure criterion defines the punching strength mainly as a function of the radial rotation of the slab in the vicinity of the column. Even if a punching failure is predominantly a shear failure, the vertical displacements and the plate rotations before failure are governed mainly by the flexural characteristics of the slab. A computational model for the flexural behavior of concrete slabs has been developed, considering the different material non linearities and allowing also to include the effect of prestressing. Finally, both the failure criterion and the computational model are merged into a physical model which is able to determine the punching strength of symmetrical slabs, with any flexural reinforcement layout (prestressed or not). The comparison between theoretical and experimental results shows good agreement, better than provided by current codes of practice. With this physical model, it is also possible to determine the punching strength for particular cases, not covered by building codes. For instance, in the case of an inner column at a flat slab, it is possible to compute the enhanced punching strength due to the restraint effect exerted by the rest of the slab. The model can also be used to determine the failure load of a foundation plate, considering the interaction between the soil pressure and the slab displacement. Furthermore, it is possible to include temperature effects on the punching strength evaluating the loss of resistance due to fire exposure of the slab. The proposed model is very flexible and can easily be adapted to the different cases which an engineer is confronted to. It revealed itself as a very helpful tool for determining the failure load of an existing structure as well as for designing the reinforcement layout for new projects. Within this thesis, only axisymmetrical cases have been studied. To analyse border or edge columns as well as other non symmetrical cases, the model should be adapted.

Punching shear of reinforced concrete flat slabs supported on columns is a failure mode in which the slab fractures around the column. This type of failure is sudden and can be catastrophic in nature. Punching shear generally governs the ultimate limit state design of flat slabs and slab bridges. The Critical Shear Crack Theory (CSCT) developed by Prof. Muttoni can be used to calculate the punching shear strength in axis-symmetrical cases. The main objective of this work was to investigate non-symmetrical cases of punching shear and to extend the CSCT to such cases. The failure criterion proposed by Prof. Muttoni allows estimating the punching shear strength in terms of the slab rotation in the radial direction. A more general model is needed to predict the punching shear strength of slabs with non-symmetrical conditions. A numerical model was developed, which is based on the finite difference method, to predict the flexural behaviour of flat slabs. It takes into account the non-linear behaviour of concrete and reinforcement steel and can be applied to non-symmetrical cases and complex structures such as flat slabs with different span length in each direction and slab bridges. Moreover, this model satisfactorily predicts the behaviour of slabs with orthogonal reinforcement and general load cases. A series of punching shear tests on non-symmetrical slabs was carried out to validate an analytical approach which considers the redistribution of shear stresses along the perimeter. This refined approach provides accurate predictions of strength and slab rotations in both orthogonal directions at failure. Moreover, this approach can be a useful tool for the structural assessment of existing structures. An analytical model is also presented which extends the CSCT to punching shear cases of internal columns with moment transfer, edge columns, and corner columns, which are commonly found in practice. The comparison between the analytical and experimental results shows that the approach developed combined with the failure criterion used in the CSCT provides accurate predictions of strength and deformation capacity for internal columns with moment transfer, edge columns, and corner columns. This work was also used to validate the formulation of the first complete draft of the Model Code 2010. In this work, the punching shear behaviour of flat slabs with bent-up bars was also investigated. Bent-up bars were commonly used in the past and are still used nowadays for particular design situations. A reliable model is needed to design structures and to assess existing structures with bent-up bars. To address this, five punching shear tests were performed on symmetrical slabs with bent-up bars. The strain measurements along the reinforcement bars provided a better understanding of the anchorage mechanisms. A model was developed, which is consistent with the CSCT and provides satisfactory predictions of the distribution of strains along the bent-up bar. The proposed model can be used to calculate the contribution of the bent-up bars, which needs to be added to the concrete contribution from the CSCT to obtain the punching shear strength.

L’objectif du projet est la conception et le dimensionnement d’un pont en béton armé en précontrainte. Plus précisément, le sujet est le pont de Tiguelet, un nouvel ouvrage, qui a pour but de joindre deux routes séparées par des voies de chemin de fer. Pour améliorer l’esthétique de l’ouvrage on vise à réduire le plus possible la hauteur du tablier, en augmentant au maximum son élancement. La construction a une longueur totale de 274 mètres. La travée principale mesure 50 mètres (40 mètres si l’on considère la réduction par les piles obliques) et les autres 7 travées d’environ 30 mètres. Le pont est constitué d’une section bipoutre de hauteur variable, variant entre 1.20 et 1.60 mètres et a donc un élancement de h/l = 1/25. Le tablier a une largeur de 10.30 mètres et permet le transit bidirectionnel des véhicules motorisés. En vue d’un éventuel changement d’utilisation dans le futur, le pont a été dimensionné pour deux variantes différentes: la première avec deux voies de circulation et des trottoirs des deux côtés, la deuxième avec trois voies de circulation. L’orientation des piles et de la culée nord est de 30° par rapport à l’axe du pont, elle est faite pour avoir les lames parallèles à la voie de chemin de fer. Cette inclinaison augmente graduellement jusqu’à devenir perpendiculaire au tablier sur la culée sud. Le terrain n’a pas une grande dénivellation et l’ouvrage reste assez bas. La hauteur des piles arrive jusqu’à 9 mètres, ainsi il est important d’avoir un bon élancement. Les piles sont en forme de lames et sont soutenues par des fondations à pieux d’une longueur de 12 mètres. Elles sont disposées en « V » au nord pour réduire la portée principale du tablier et mettre en évidence la zone du chemin de fer. Les piles de la zone sud, sont verticales. La culée nord et les piles en « V » sont monolithiques au tablier, Les autres soutènements ont des appuis mécaniques qui permettent les déplacements horizontaux dans l’axe du pont. Le pont peut donc se dilater vers la culée sud, où on trouve le joint de dilatation qui reprend ces déplacements.

Une dalle à la géométrie primaire, un disque élevé à 12 m de hauteur, un geste qui, d’une part, génère l’espace de l’événement, l’alter-ville, qui se détache du sol et, d’autre part, permet aux fonctions urbaines, tel que l’arrêt du tram, la place couverte pour le marché et les ateliers dédiés à la production artisanale et artistique, de s’installer au-dessous. Ce dispositif, affirmant cette dichotomie, offre aux flâneurs en quête d’expériences singulières une fugue vers le monde de l’événement et de l’instantanéité. Le plein, le podium, une structure inébranlable, sert de support pour celle qui aujourd’hui sera une tour de logements, un camping vertical urbain pour étudiants et artistes. Chaque individu aura la possibilité de louer une loge habitable à raccorder au réseau technique de la tour, à n’importe quel étage et pour n’importe quelle durée. Le vide est occupé par un dôme monumental renversé, une structure suspendue, en lévitation, qui contient un jardin édénique. La lumière caressant la surface réfléchissante du dôme rejoint le niveau inférieur. Les passants transitant au sol, fascinés par cette forme énigmatique, irradiée par les rayons du soleil, entreprendront l’ascension vers ce monde qui se détache de la rigueur de la ville. Cette structure héroïque veut exalter l’éphémère et l’événementiel. Une structure qui a la force de devenir la scénographie immuable pour une société en mouvement.

The present research on cut-and-cover tunnels gives a theoretical contribution to the understanding of the behaviour of these structures up to their ultimate limit state. A simplified method inspired on the convergence-confinement method is investigated and applied systematically to several practical cases. This method, based on the failure mode of the structure, gives an approximate solution of the equilibrium between the soil and the structure. It enables a better understanding of the complex soil-structure mechanisms, typical of these constructions, constituting in this way a design tool. The behaviour of the soil which interacts with the structure comprises typically two main phases. The elastic phase is followed by the progressive yielding of parts of the soil until a plastic mechanism is formed (plastic phase). Depending on the geometrical and the mechanical parameters, the structure takes more or less advantage of the soil contribution in carrying the loads. The main conclusion of this work is the demonstration of the existence of different modes of behaviour. Three main modes of practical interest, defined mainly by the phase of the soil governing the structural behaviour, are distinguished : elastic soil, elasto-plastic soil and completely plasticized soil. The identification of the mode then enables an efficient design and analysis of the structure. The theory of plasticity (upper bound) was applied to two soil-structure systems, a surface strip footing submitted to a centred load and a lateral wall of a frame-type cutand- cover tunnel under construction, aiming at studying their behaviour at the ultimate limit state. This study clearly emphasizes the favourable or unfavourable role played by the soil-structure interaction in the collapse of such structural systems. A proper consideration of the structure failure kinematics is thus fundamental to a proper representation of the ultimate limit state. A new safety format is proposed to define the ultimate limit state when the finite element method is used. This safety format is compatible with the new SIA codes of practice and clarifies the structural design procedure. The research also showed that the structure's ductility plays a major role in the development of the structural soil capacity. Several ductility limits are emphasized for cut-and-cover tunnels. For frame structures, the deformation capacity of the top slab is very small if no shear reinforcement is provided in the zones of significant shear forces. Stirrups are thus recommended in these structures. For arch structures, the spalling of the concrete cover can limit the deformation capacity of the structure. Experimental tests performed within this research showed that this phenomenon was affected negatively by plastic deformations of the steel reinforcement and by reinforcement splices and anchorages. SIA 262 (2003) code of practice design criterion is judged insufficient. The structural design of cut-and-cover tunnels with important plastic redistributions is thus possible only if certain ductility conditions are fulfilled.

L’usine disparaît progressivement des centres urbains européens, les zones industrielles se déplacent en périphérie ou à la campagne, se situant dans d’énormes bâtiments à un étage; leur emplacement précédent attribué à des logements ou des bureaux, les bâtiments les plus anciens reconvertis et les plus récents démolis. C’est dans cette situation que se trouve actuellement la zone du PAV (Praille-Acacias-Vernets) à Genève, où des nouvelles constructions – pour la majeure partie des blocs résidentiels – remplacent l’ancien tissu industriel, datant des années 60 et 70. Les nouveaux développements sont divisés sur un plan horizontal selon le programme. Le projet questionne cette division. Garder l’usine au sein de la ville, sans y exclure d’autres programmes? Sans exclure le logement qui manque tant à Genève? Il vise à transformer l’usine en un hybride, où industrie, logement, bureau et loisir se côtoient. Divisée verticalement, et non plus horizontalement, l’indétermination programmatique spécifique à l’usine est mise à profit de nouveaux programmes qui peuvent être insérés dans le bâtiment, exploitant à l’extrême le principe de flexibilité. C’est une proposition qui critique le principe moderniste du cantonnement des fonctions et qui propose un prototype de mixité urbaine qui puisse maintenir l’usine dans la ville.

Flat slabs are commonly used in Switzerland but also in north America and in many European countries. Slab bridges are also a typical solution for crossing of motorways for example. In both cases, supporting a slab by columns is justified by the simplicity and the easyness of construction. When spans increase (larger than 8 to 10 m), the use of prestress becomes almost systematic. The deviation forces of prestressing lead the concrete to be subjected to normal forces, moment in the opposite way as those created by downward acting loads, and vertical components due to the geometry of prestressing tendons over the slab length. The zone in the vincinity of the column subjected to punching is thus also affected by various effects of the prestressing. The aim of this work is to investigate individually the influence of each of them on the punching shear strength. To achieve this goal, various tests programmes were performed. The first one aimed at understandinng the influence of a moment acting in the opposite way as those generated by downward acting loads. The second one at understanding the influence of a normal force on punching shear strength. The third one gathered the two others by including prestressing tendons in the slabs, leading simultaneously to a moment and a normal force. It has been shown that each of the prestressing parameters has a significative influence on punching. The moment allows to increase punching shear strength and the deformation capacity tends to be reduced. The normal force tends also to increase punching shear strength but the deformation capacity is less affected as for the moment. The main current design codes do not take into account all of these effects of prestress on the punching shear strength and do not deal generally with the influence of the prestressing induced moments. A formulation almost identical for Model Code (2010) and SIA 262 (2012) has been proposed allowing to consider every prestressing parameter. The tests series enable in particular to validate this new formulation. Moreover the critical shear crack theory originally proposed by Muttoni and the failure criterion have been improved on the basis of a theoretical model taking into account the various effects of prestressing. The model is based on the kinematical behaviour of the slab measured on a specific test series performed during this work. A load-rotation law has been developped on the basis of the quadrilinear law initially proposed by Muttoni enabling to consider the influence of the moment and the normal force due to prestres- sing on the specimen behaviour. Finally, a simplified failure criterion has been proposed, extending the original criterion of Muttoni.

Flat slabs are commonly used in buildings due to their easiness of construction and economy. In order to keep these advantages, columns are usually not continuous through the slabs in multi-storey buildings. In these cases, the slabs are subjected to large compressive stresses at the support area of the columns, which can exceed the uniaxial compressive strength of the concrete of the slab. This critical zone is in addition subjected to large shear forces and bending moments due to the loads applied on the slab. This leads to a series of potential failure modes: crushing of the concrete of the slab between columns, flexural failures or punching shear failures. Most research has previously focused on the influence of bending of the slab on the column strength. However, no works have provided in-depth investigation of the strength of the slab when large column loads are applied. In this research, an extensive experimental program has shown that the stresses applied at the support area of the columns can be significantly larger than the uniaxial compressive strength of concrete. The test results have clearly shown that no special confinement or load transfer devices are required between columns for most cases (moderate column loads). In addition, two phenomena have been observed. The first one is a reduction on the flexural strength as column loads are applied. The second corresponds to a significant increase on the punching shear strength and deformation capacity with column loading. Existing theoretical approaches for flat slab behaviour and strength are shown not to be directly applicable for slabs subjected to large column loading. In this research, the principles of two general theories (the theory of plasticity and the critical shear crack theory) are thus used to investigate such cases. The theory of plasticity allows calculating a plastic failure envelope accounting for bending and column loading, whereas the critical shear crack theory, which in this work as been further investigated theoretically, is used to derive a failure criterion accounting for punching shear failure in presence of column loading. The results for both theories are finally presented in terms of a single interaction diagram between column loading and slab loading (bending and shear of the slab). The theoretical approaches require however the help of rather refined numerical tools for estimating the strength of a flat slab. In order to use the theoretical approaches for design, a simplified approach has been developed, allowing to calculate the strength as well as the deformation capacity of flat slabs. These tools were implemented in a design method for slab-column joints in multi-storey building. This design approach allows to derive simplified interaction diagrams that can be compared with the loading history of the structural element analysed.

Sustained load actions are permanently present in concrete structures, as for example self-weight and dead loads on bridges or soil pressure on cut-and-cover tunnels. These actions may increase throughout a structure's lifetime, for instance after refurbishing or in the case of addition of new elements. It has been experimentally observed that under sustained load actions, the response of concrete may be significantly different than the response under rapid loads. Traditionally, sustained actions are treated differently at serviceability limit states (for instance delayed deflections) than at the ultimate limit state (as the potential failure under sustained load). The distinction is given by separating the time-dependent deformation due to linear creep from the strength reduction due to nonlinear creep. Although quite practical, this approach is not sufficient to understand the phenomenon of strength reduction under sustained loads and the potentially beneficial effects of the delayed response of concrete. The present thesis introduces a comprehensive approach for the long-term analysis of concrete structures, allowing to consistently investigate the response both at serviceability and ultimate limit states. The first part of the thesis aims at establishing a theoretical framework for the evaluation of the time-dependent uniaxial compressive strength of concrete under sustained loads. Based on this work, it is demonstrated that the strength reduction is more severe under a constant sustained load than in the case of loads increased with a low loading rate. In addition, both the mechanical approach and the conducted tests show that the detrimental effect of sustained loading is associated with a potentially beneficial increase of deformation capacity at failure. Within this framework, typical engineering design situations are addressed, such as the case of application of a variable action after a period of sustained loading. The time needed for the continued cement hydration to overcome the detrimental effect of sustained loads is also investigated. The second part of the thesis aims at verifying whether the shear strength of members without transverse reinforcement is influenced by the action of sustained loads. It could be shown that there is no marked decrease of the shear strength for longer durations of application of the load or very low loading rates compared to typical shear tests. This behaviour is supported by detailed observations performed by means of digital image correlation, allowing to quantify the contribution of the various potential shear transfer actions. This work has resulted with several proposals for improvement of codes of practice.

Certaines poutres disposent d’étriers partiellement ancrés pour des raisons constructives ou parce qu’elles ont été construites dans le passé de cette façon. De ce fait, les calculs habituels de type rigide-plastique ne sont plus valables et un changement de comportement à la rupture est possible. Dans le cadre de ce projet de Master, une étude approfondie de cet effet est proposée. Une attention particulière a été portée sur le phénomène de l’adhérence dans le cadre de la théorie de l’élasto-plasticité à l’aide d’un logiciel de modélisation non-linéaire (jConc). La plupart des approches conventionnelles sont fondées sur des lois complexes d’adhérence dérivées d’essais d’arrachement dans des milieux non-fissurés. Néanmoins, il a été montré récemment que la fissuration affecte de manière significative la performance de l’adhérence. Cet effet peut donc être difficilement négligé : c’est particulièrement le cas pour des étriers ayant des extrémités non-ancrées plongées dans une zone fortement fissurée (partie tendue de la poutre). Afin de prendre en compte ce processus physique systématiquement délaissé, une approche novatrice est proposée pour prendre en compte le degré de fissuration et sa conséquence sur la qualité de l’ancrage des étriers. Plusieurs modélisations ont été effectuées sur des poutres présentant des défauts d’ancrages aux étriers, pour vérifier le fonctionnement de ces élèments. Outre la faible variation de la charge de rupture, une profonde redistribution des contraintes a été observée. Un ancrage faible tend à abaisser l’angle des bielles, à solliciter les étriers à l’écoulement de manière plus locale et à augmenter le degré de fissuration du béton. L’écartement des étriers (pour un même taux d’armature) a été identifié comme étant un paramètre potentiel clé dans l’apparition d’un mécanisme de rupture propre à ce type de poutre. L’outil développé aura un grand intérêt pour des futures études à propos du comportement d’élèments de structures présentant des armatures dans des conditions sévères de fissuration.

This thesis applies structural optimization techniques to develop a general methodology for design from reuse. A thorough case study serves as proof-of-concept. Reusing elements from dismantled structures appears as a promising, yet little explored approach to respond to current environmental challenges faced by the construction sector, namely limitation of natural resources, carbon footprint reduction and waste management concerns. Compared to a conventional design approach, the usage of reclaimed elements introduces additional geometrical and mechanical constraints to the structural problem. The structural layout becomes function of given elements, e.g. their quantity, length, cross-section, strength and connection details. Up to date, applications of structural reuse mostly comprise case-by-case empirical approaches that do not explore the solution space. To recover design freedom, this thesis proposes the development of structural optimization techniques based on the consideration of a stock of reused structural elements. The approach has the advantage of generating optimal solutions for reuse while enabling design explorations. The second part of this thesis is a case study that illustrates the theoretical methodology. In particular, the design of a new roof cover for the Lausanne’s train station is investigated. This hypothetical project considers the reuse of a real stock of structural elements from 322 electric pylons to be dismantled in 2020. The outcome of this case study is twofold; it validates applicability and at the same time it informs future theoretical prospects.

Les dalles des ponts en béton sont dotées de barres d'armatures transversales dans le but de reprendre les efforts de flexion, dû au poids propre et aux charges utiles. Ces barres ont un rôle supplémentaire, celui de diffuser les efforts de flexion longitudinaux dans la dalle, afin qu'ils puissent rejoindre l'âme et par la suite, les appuis. Ces effets de déviations peuvent être très importants sur appui dans les semelles tendues, allant jusqu'à créer des ruptures inattendues par manque d'ancrage des barres longitudinales. À ce jour, la norme sur les structures en béton de l'Eurocode EN 1992-1-1 datant de 2004 a été révisée. L'étude principale de ce projet de Master concerne la validation de l'article 8.2.5 du draft permettant de dimensionner ces armatures transversales. Afin de pouvoir modéliser et analyser ces effets d'une manière simplifiée, l'étude s'est focalisée sur une poutre bi-appuyée ou bi-encastrée, à l'aide de jConc, un logiciel développé au laboratoire de béton de l'EPFL. Ce logiciel permet de dessiner des éléments sur un plan 2D, mais le phénomène décrit ci-dessus ne se développe pas sur les mêmes plans. La première partie de ce projet a été de trouver une façon simple et efficace permettant de modéliser les trois éléments de la poutre, l'âme et les deux ailes, sur un seul et même plan. Par la suite, le comportement de la poutre a été étudié, en la dimensionnant à l'aide de l'Eurocode. Ces différentes modélisations ont permis de comprendre les types de rupture qui peuvent intervenir dans la poutre et les points faibles de chacun des systèmes statiques. Enfin, une étude paramétrique des différents taux d'armatures de la poutre a été réalisée. Cette étude a permis de contrôler les différents paramètres de l'article de l'Eurocode, comme les déformations longitudinales, les facteurs de réduction de la résistance du béton et des différentes bornes limites des angles des bielles, dont une recommandation a été faite en fin de rapport.

L’adhérence est une propriété du béton qui dans les structures en béton armé, est activée sur une très longue période de temps. En fait, des mois, voire des années, peuvent se passer avant que le béton n’atteigne un état de contrainte significative. La plupart des études réalisées jusqu’à présent sur cette propriété très importante ont été menées à court terme, par conséquent, dans ce projet, nous voulons réaliser des études sur cette propriété à long terme afin de pouvoir comprendre son réel comportement. Grâce aux résultats obtenus à partir d’une série d’essais réalisés, il a été conclu que les durées d’essai utilisées étaient probablement trop courtes par rapport aux durées réelles des charges sollicitant les structures réelles en béton armé. Ceci peut être affirmé parce qu’aucune influence importante de la durée de l’application de la charge sur les valeurs de la force d’adhérence obtenues par les essais de pull-out n’a été constatée. D’autre part, on a remarqué comment la position des barres à l’intérieur de la section influence fortement les résultats, en effet ils se révèlent très différents les uns des autres selon que la barre se trouvait au moment du test dans la position favorable ou défavorable de la section, on a remarqué comment, surtout pour de petites valeurs d’enrobage, il y a une influence importante d’une telle position allant à confirmer les théories déjà présentes. La deuxième partie du projet concerne l’étude des longueurs d’ancrage des barres d’armature noyées dans le béton, qui sont réalisées à partir des résultats d’essais obtenus dans la première phase de ce travail. Il a été ainsi possible de faire plusieurs considérations sur les résultats obtenus, en effet, on a vu comment le choix des valeurs de départ influence particulièrement les résultats finaux et qu’en général la contrainte de traction qui est introduite du béton à l’acier par le biais de l’adhérence suit une tendance initialement purement linéaire et se transforme ensuite en un comportement curviligne.

Reinforcement detailing rules describe the shape, geometrical dimensions, and amount of steel to be placed in reinforced concrete structures. They allow for simple and fast designs, account for several effects neglected in the design, ensure a satisfactory behaviour under serviceability conditions, a sufficient robustness, and an adequate behaviour in case of unexpected actions. Most detailing rules provided in codes have not been updated to correspond to current manufacturing processes, material performances and scientific knowledge. They are often based on "rules of good practice" which, while satisfactory, lack a sound scientific basis and may not be needed. This is one reason why detailing rules may differ amongst countries and design codes. Some of these rules are overly conservative, in particular when evaluating existing structures, while others may neglect significant effects. Even though these rules play a major role in the economy and safety of concrete structures, little research has been performed in this domain. Several detailing rules have been identified as needing additional investigations to verify their adequacy to current practical needs and recent technological evolutions. This thesis presents a research programme on three main detailing rules: bend detailing and required mandrel diameter, anchorage of shear reinforcement with bends and hooks and minimum amount of shear reinforcement. This research aims at developing mechanical models, simplified formulas and detailing provisions, on the basis of experimental results. These were obtained using state-of-the-art measurement techniques such as Digital Image Correlation or Fibre-Optic Measurements. Bends and hooks of reinforcing bars are usually obtained by plastic bending of the bars against mandrels. Codes specify minimum mandrel diameters to avoid splitting or spalling failures that may limit the resistance of the detail. The thesis includes a research programme on the detailing of bends and the required mandrel diameter to avoid concrete failures leading to spalling of the concrete cover. A mechanical model for the design of bent reinforcement was developed. A simplifying standard bending procedure is proposed, in which details formerly requiring various bend diameters can be obtained by using a single mandrel, allowing for faster automated manufacturing of bent reinforcement. Bends and hooks at the end of the bars are efficient solutions for the anchorage of reinforcement. However, these details are relatively sensitive to the cracking state of the surrounding concrete. For shear reinforcement, spalling failure of the concrete cover for bars close to the concrete surface can occur. The thesis includes an investigation on the mechanical response and performance of bend and hook anchorages. A mechanical model and practical considerations on the activation of shear reinforcement in beams are presented. The required minimum amount of shear reinforcement in beams and slabs has been discussed for decades. It is crucial to ensure economic and safe new structures and to accurately assess existing ones. The investigation shows that the shear behaviour is strongly dependent on the amount and the post-yield response of the shear reinforcement (ductility class). For all investigated detailing rules, the implementation of these findings into codes is discussed, highlighting the consistency of the recent changes, particularly with the new generation of Eurocode 2.

Over the past decades, an increasing number of integral bridges have been built. This type of bridge offers various advantages in comparison with standard bridges equipped with expansion joints and bearings. In particular, integral bridges require less maintenance since they have less mechanical elements. Therefore, cost of retrofitting and indirect costs such as time spent by users during the maintenance works is reduced. Moreover, the static efficiency is increased and the noise of circulation during its lifetime is reduced. However, for the design and analysis of this kind of structure, the soil-structure interaction needs to be investigated to take in account the monolithic behaviour of the bridge with the embankment near the abutment and the piers with the foundation. This interaction is complex and further research is needed. The report begins by a general introduction of the topic. Thereafter a brief description of the state-of-the-art on integral bridges is presented, as well as the main difficulties faced during design and the main actions that need to be considered. Limit states and numerical analysis on integral abutments and pier on shallow foundations are discussed towards a better understanding of the structural behaviour in order to improve current detailing and design practice. The study of integral abutments shows that soil-structure interaction should be considered at early stages of the design process. This allows introducing small geometric adaptations to improve detailing which in turn allows significantly increasing the long term performance of the integral abutment without a sensible increase of building costs. This set of new rules can further be applied to both new and existing bridges which require retrofitting of the expansion joints at the abutments. The study of the cracking limit state of piers shows the strong influence of the geometry of the shallow foundations on the soil-structure interaction. This two studies show that geometric adaptation in combination with accurate soil-structure modeling could lead to an increase of the current Swiss limit length for integral bridges which is now set at fixed to 60m.

Every engineering calculation is an approximation of reality, with inevitable uncertainties involved. This fact implies that a reliability verification accounting for the uncertainties is a necessary step in the design and assessment of structures. Nowadays, probability-based partial safety factor format is widely adopted in the structural reliability verification in design codes. The safety format calibration is a continuing updating process with the advancements of knowledge in structural engineering. For reinforced concrete structures, open questions for the safety format calibration emerge with the increasing application of advanced nonlinear structural resistance analysis approaches (e.g. strain-based approaches and numerical methods like the NonLinear Finite Element Analysis) as well as the application of new materials. Aiming at meeting these new challenges, several topics within the partial safety factor format framework are investigated. In the first part of this work, the simplifications and assumptions in the classical partial safety factor format for the resistance of reinforced concrete structures are examined. Their suitability for the implicit nonlinear analysis models is investigated focusing on the influence of multiple failure modes. Reliability analysis case studies at different scales (cross-sectional resistance or load-bearing capacity of structural elements and of simple structural systems) show that the partial safety factors applied to material strength variables leads to a satisfactory level of reliability, independent of the development of different failure modes induced by material uncertainties. In the second part of this work, the characteristic of the model uncertainties of strain-based approaches is investigated using the punching shear resistance model based on the Critical Shear Crack Theory (CSCT) as an example. It is shown that the model uncertainty of global resistance solution of strain-based approach can be viewed as the resultant of the model uncertainties of the sub-models. In addition, the model uncertainty of the global resistance solution can be lower than those of the sub-models, depending on their sensitivity relationship. Based on these observations, different types of partial safety formats for strain-based approaches are compared. The relationship between the safety factors of the punching shear provisions in the second generation of Eurocode 2 for the design of new structures and the assessment of existing critical ones is established. The last part of this work deals with the partial safety factor format calibration problem for structures with brittle response. As an example, the partial safety format for the flexural resistance of Textile Reinforced Concrete (TRC) is calibrated focusing on the model uncertainties of action effect for brittle systems. Based on these works, it is concluded that a suitable probabilistic modelling of the basic uncertainties is fundamental for the effective calibration of the partial safety format and it should be based on a good understanding of the relevant load bearing mechanisms. On its basis, a detailed safety format composed of calibrated partial safety factors for the dominating uncertainties is an effective reliability verification approach for both classical analytical design equations and advanced nonlinear analysis methods.

Since the first applications of structural concrete, the shear behaviour of one-way slabs without transverse reinforcement has been largely investigated. Nevertheless, currently in the scientific community there is no general agreement on the mechanisms of shear failure, on the parameters governing the shear strength and on the predominant shear-transfer actions. Hence, several mechanical models, based on very different hypotheses, and empirical formulations, calibrated on the available experimental results, have been proposed in the last decades. In addition, these experimental results have been traditionally obtained from tests on simply supported beams subjected to point load, whereas in most one-way slabs without transverse reinforcement in practice (foundations, retaining walls, slabs of cut-and-cover tunnels, silos) the boundary and loading conditions are typically different. This thesis has therefore the objective to provide new experimental data on reinforced concrete members without transverse reinforcement tested with different loading and boundary conditions, to increase the understanding on the mechanisms of shear failure and to develop a mechanical model based on the new experimental evidence. In the first part of the thesis, the experimental results of 23 tests on 20 beams without transverse reinforcement subjected to different loading (concentrated or distributed) and boundary conditions (cantilevers, simply supported or continuous beams) are presented. Refined measurement techniques allowed detailed tracking of the development of the crack pattern up to failure. The results show that the location, inclination and kinematics of the critical shear crack play a major role on the shear strength. Moreover, the amount of shear transferred by the various potential shear-transfer actions has been estimated on the basis of the experimental measurements and by using suitable mechanical models for each shear-transfer action. The analyses show that, for slender members, the shear-transfer actions contributing to the shear capacity are the inclination of the compression chord, the residual tensile strength of concrete, the dowelling action and the aggregate interlock, and the latter is the predominant one. For squat members or members in which the critical shear crack develops below the theoretical compression strut, differently, the arching action is predominant. In the second part of the thesis, a mechanical model, consistent with the main ideas of the critical shear crack theory, is presented. The shear force that is transferred through the critical shear crack by the various shear-transfer actions is calculated by integration of simple constitutive laws and a failure criterion is obtained by summing the different contributions. The shear and deformation capacity can thus be calculated by intersection of the failure criterion with a load-deformation relationship. It is shown that the failure criteria obtained by integration of stresses at the crack surface can be approximated by power-law equations. Combining the power-law failure criteria with the load deformation relationship, a closed-form equation has been obtained. The closed-form equation provides almost identical results to the mechanical model and allows for direct design and assessment of existing structures. The accuracy of the mechanical model and the closed-form equation has been checked against a large database, showing a good agreement to the experimental results.

The objective of this work concerns the analysis and design of an existing deep beam with a high thickness in reinforced concrete, according to the standards defined in the Eurocode. The structure is inserted in a hydroelectric plant in the Alentejo region of Portugal. The initial data is used to define the geometries parameters and the loads based on the deep beam. The analysis began with a study of its environment, in order to determine the different actions and the loading for the ultimate limit state and the state of service. The analysis is followed by a study of numerical values known for simple cases in the elastic domain, then by an elastic analysis with finite element software IConc and finally with the strut and tie models. During the dimensioning step, the modeling of the structure was performed by the SAP2000 finite element software, in the order to evaluate the stresses resulting from the defined actions. This is followed by performing of the safety checks and reinforcement calculations for the ultimate and serviceability limit states, for the deep beam, but also for the columns. A detailed reinforcement plan could thus be created. Subsequently, thanks to the considered reinforcement arrangement, a verification at failure was performed by using the IConc software again and assuming an increase in the mobile loading. An optimization of the thickness of the web was also reflected, as well as the possibility of removing one of the columns, with the establishment of prestressing.

Au cours du siècle dernier, les grandes infrastructures hydrauliques ont souffert du nouveau régime climatique. Situé au pied du glacier du Rhône, lieu grandiose et chargé symboliquement, le projet propose d’explorer le devenir du paysage alpin au travers d’une structure nouvelle qui dépasserait sa condition de pure utilité. Le Rhonegletscherdam marque la fin de la conquête de l’hydraulique en proposant une alternative de forme et d’usage au barrage traditionnel. Grâce à sa forme pure et compacte isolée dans un paysage hostile et dépeuplé, il synthétise la mémoire du lieu et l’expérience sensorielle humaine, tout en permettant de s’affranchir de l’étalement urbain qui a peu à peu défiguré les versants alpins. En effet, outre sa capacité à retenir une immense masse d’eau, le projet condense en son sein une ville composée de résidences secondaires valaisannes autour desquelles se trouve un assortiment de programmes destinés à la santé de l’homme sous tous ses aspects. La vie dans l’infrastructure s’articule selon deux axes programmatiques. L’utilisateur cherche la tranquillité de l’esprit et la performance du corps. L’ensemble des activités proposées grâce aux conditions climatiques particulières (altitude, soleil, température) vise à augmenter le bien-être corporel et à apaiser l’esprit. Les services proposés par cette grande résidence d’altitude tendent à limiter les effets du temps et de la vie contemporaine sur le corps. Bienvenue au Rhonegletscher Health and Wellness Center.

Le secteur de la construction constitue l’un des domaines les plus polluants de l’activité humaine. Ceci est principalement dû à la très large utilisation du béton, qui demande beaucoup d’énergie lors de la fabrication du clinker. De plus, la quantité de ressources utilisée pour le produire : la roche calcaire, l’eau, le sable et les granulats, est limitée. C’est pourquoi une utilisation plus juste des matériaux de construction est nécessaire pour limiter notre impact sur l’environnement. Les mauvaises conceptions et mises en oeuvre peuvent engendrer des dégradations des ouvrages sur leur durée de vie. Certaines peuvent causer des problèmes de sécurité structurale mettant en péril la durée de vie de l’ouvrage. Lorsque c’est le cas, les Maîtres d’ouvrage, les ingénieurs civils et les entreprises de construction doivent agir en procédant à un renforcement ou un remplacement des éléments problématiques. La reconstruction complète d’un ouvrage est très coûteuse et nécessite énormément de ressources. Parfois il s’agit de la solution la plus adéquate, mais parfois le renforcement d’un élément permet d’augmenter la durée de vie d’un ouvrage pour une intervention plus rapide et moins onéreuse. Cette étude concerne l’utilisation de béton-textile (TRC) pour le renforcement d’un ouvrage d’art à l’effort tranchant. Des simulations à l’aide du programme Jconc ont été créées pour évaluer la résistance théorique du matériau sous plusieurs formes : effort tranchant pur, traction pure et utilisation comme renforcement sur une poutre armée avec des taux d’armature conventionnels. Il en a été déduit que le mortier textile constituait une bonne solution pour le renforcement à l’effort tranchant, et qu’il était plus efficace que de l’armature traditionnelle lorsqu’il est couplé à du béton à haute résistance. Les résultats montrent aussi qu’un tel renforcement est capable d’augmenter la résistance de la poutre à l’effort tranchant, mais qu’elle est limitée par la résistance en flexion de la poutre. Ces modèles n’étant que théoriques, une campagne d’essais a été réalisée pour compléter des résultats obtenus lors de l’automne 2020. Ils visaient à étudier l’effet d’ancrages sur une éventuelle rupture de la couche de mortier par délamination. Il en a été conclu qu’une longueur d’ancrage de 200 mm était suffisante pour ancrer les fibres dans le mortier, mais que des ancrages sont probablement nécessaires pour ancrer la couche de mortier dans le béton. La faible quantité d’essais effectués ne permet cependant pas d’affirmer ces hypothèses avec certitude mais constitue une bonne base pour une proposition de renforcement. Une intervention a ensuite été proposée sur le pont des Grands-Crêts, dans la commune des Clées (CH), à la suite de l’identification des parties d’ouvrage critiques. Elle est basée sur deux variantes imaginées avant que les essais aient été effectués, c’est pourquoi des propositions de modifications ont été établies après l’analyse des résultats des campagnes d’essais. Finalement, le renforcement TRC est une solution adéquate pour renforcer un ouvrage d’art à l’effort tranchant pour autant qu’une mise en oeuvre adaptée soit effectuée. Les points clés d’une bonne mise en oeuvre ainsi que les matériaux et matériels nécessaires à la réussite du renforcement sont présentés dans cette étude.

Le béton textile est un nouveau matériau qui combine les propriétés d’une armature non-métallique coulés dans une matrice à base de ciment à haute résistance. C’est un matériau performant tant pour ses qualités structurelles qu’en terme d’application en développement durable et en recherche architecturale. L’état des connaissances sur le béton textile est peu avancé. Des applications pour ce matériau existent, mais ne sont pas utilisées du fait de l’absence de normes régissant son utilisation. Ainsi depuis une vingtaine d’années, différents laboratoires universitaires, développent des projets de recherche autour de ce matériau afin de mieux connaitre ses propriétés et de le rendre exploitable à grande échelle. Ce projet de master a pour but de conceptualiser, pré-dimensionner, construire et tester une poutre en béton textile. La poutre sera caractérisée par une section variable et des parois minces. L’objectif sera de montrer la faisabilité d’un tel élément et de montrer dans quelles mesures il peut être préfabriqué. Grâce au coffrages fabriqués durant ce projet, une poutre de trois mètres et une poutre de cinq mètres ont été coulées. Nous verrons en détail comment cela s’est passé, et comment cela ouvre une porte vers la préfabrication.

Designing new concrete members and assessing the strength of existing elements subjected to in-plane stress state conditions is often conducted by means of Stress Fields (SF) and Strut-and-Tie Models (STM). These methods are usually accounting for identical load-carrying mechanisms for design and assessment, even if the goals for these two tasks are not the same. When designing new elements, the aim is to obtain solutions that are in equilibrium with external actions, with simple reinforcement layouts while ensuring satisfactory behaviour at serviceability limit state. When assessing the ultimate strength of existing elements, the goal is to avoid an unnecessary strengthening and limit the amount of retrofitting. The required complexity of assessment models depends on the strength requirements, and need to be gradually refined if the results from current models prove to be insufficient. This refinement process ultimately leads to increasingly more exact solutions that eventually correspond to the largest possible strength according to the limit analysis. This thesis presents various strategies which can be employed to develop SF and STM suitable for the design and assessment of structural concrete members. The idea of a gradual model refinement (both for design and assessment) is introduced through practical examples, while potential challenges related to each solution are indicated and discussed. Moreover, the accuracy and the generality of exact solutions obtained using Elastic-Plastic Stress Fields (EPSF) are investigated. To do this, ultimate loads estimated with EPSF are compared to test results found in the literature. To facilitate further studies by other researchers, they are available online. The analysis of structural members with insufficient anchorage and indirectly supported concrete elements with EPSF are presented and discussed. Furthermore, this thesis focuses on a sensitivity analysis of the EPSF, to investigate the stability of the results as a function the size, shape and orientation of the finite elements. The influence of the number of iteration steps on the accuracy of EPSF models is evaluated, and clear recommendations are provided. Stress fields based on exact solutions of the theory of plasticity simulate the physical behaviour of structural concrete members more accurately than current code provisions. On this basis, a procedure for tailoring partial safety factors for steel and concrete is presented and discussed. Reduced PSF could potentially be used when assessing the strength of existing reinforced and prestressed concrete elements, which would (could?) lead to significant cost reductions in the field of structural maintenance. To better understand the mechanical origins of concrete compression softening (important for an accurate application of stress fields), a mechanical model for estimating the effective concrete compressive strength is developed and discussed. Concrete cover spalling, concrete crushing and crack sliding are taken into account. Special attention is given to the dowel action of the reinforcement and its effects on the surrounding concrete matrix. The model is validated using experimental results found in literature. Finally, the pertinence of existing semi-empirical approaches for determining the effective concrete compressive strength is evaluated and discussed.

The design of reinforced and prestressed concrete girders is usually performed so as to avoid any non ductile failure mode. Amongst these failure modes, one of the most undesirable occurs by crushing of concrete in the web. To avoid this brittle type of failure, it is of paramount importance to know precisely the effective compressive strength of concrete in the web. It is reduced by cracking (transverse strains), which is due to the shear deformations. In the presence of post-tensioning cables in the web, cracks may form along the cables inside the web, which also weakens the concrete of the web. Numerous bridges have been built in Switzerland by using profiled girders with thin webs containing only a minimal amount of stirrups but large post-tensioning ducts, which occupy a considerable part of the web width. Both phenomena mentioned above play a role for these bridges, especially for more brittle high performance concrete. The two phenomena are only partly understood. A sound physical model for the shear behaviour as well as a failure criterion are necessary to achieve a uniform safety level for new structures and to evaluate the strength of existing structures. Large-scale laboratory tests on prestressed concrete girders have been conducted in order to improve understanding and to investigate both phenomena in detail. Web crushing along the post-tensioning cables was the mode of failure of all girders. In addition, laboratory tests have been conducted on prismatic specimens to investigate the effect of the presence of a post-tensioning cable in an isolated manner. A physical model has been developed for the shear behaviour of reinforced and prestressed concrete girders. The variation of loading, stresses and strains along the girder axis is taken into account. The shear capacity of the compression flange is considered on the basis of equilibrium and compatibility. The load increase in the post-tensioning cables is calculated with a bond condition. A physical failure criterion has been developed for the effect of the presence of a posttensioning cable. The failure load of the conducted prism tests and a large number available in the literature has been estimated with a good precision for various post-tensioning duct types and concrete cylinder strengths. Based on physical considerations a failure criterion has been developped that takes into account the effect of transverse strains. Both effects are more pronounced for a higher cylinder strength. With the developed physical model and the failure criteria, the failure load of a large number of reinforced and prestressed concrete girders (laboratory and from the literature) has been estimated with good precision. The interaction of the effects of the presence of a post-tensioning cable and of transverse strains has been taken into account for the development of a combined failure criterion. Its format is compatible with the current design codes.

For various types of civil structures such as bridges, skyscrapers and other slender towers, oil rigs as well as runaways, dynamic loading is predominant. This holds true especially for bridges where loads have increased considerably in the last hundred years. It is in this context that further research in the behaviour of concrete elements subjected to cyclic loading is justified and required. Within this specific field of research there exist multiple angles of attack. On the one side, one can try to better understand the fatigue life by doing long-term analysis with several million cycles to predict the failure under fatigue loading depending on stress ranges, rebar types and other parameters. On the other hand, the study of the cracking behaviour of elements under cyclic loading is just as pertinent as it allows a more fundamental understanding of the mechanical process to which cracks are subjected. This second area of research includes fracture mechanics, residual stresses as well as the loading type (tension or bending). Three beam type samples with geometry of (l = 3.00 m, b = 0.30 m and h = 0.32 m) are tested under cyclic loading, applying three different levels of load (24, 50 and 80 kN). The reinforcements are limited to longitudinal bending without any transverse ties. To observe shear as well as flexion cracks on the same sample, a 4-point bending configuration is chosen and at least 50 loading-unloading cycles are performed until stabilisation crack opening is observed. For most of the past research on structural elements which are similar to those tested for this project, strains are usually measured by gluing strain gauges onto a sample leading to very localised strain data. In the present case, a recently acquired system from LUNA FIBRE OPTICS using optical fibers which are glued onto the reinforcement bars is used to measure the complete strain profile all along the sample giving a much more detailed insight into the variations of the strain, especially around cracks. During the course of this project, all necessary procedures with regard to fiber handling and data acquisition are developed and tested. It could be shown that optical fibers present a promising addition to existing instruments, allowing for very detailed analysis of strain profiles by increasing the amount of available data considerably. Furthermore it has been shown that even at low numbers of cycles, there is a significant decrease in shear resistance due to uncontrolled shear crack development. While samples SC75 and SC76 (which represent 27% and 56% of the shear resistance of the sample) show stabilisation of crack openings and fiber strain, sample SC77 at 89% of the resistance failed prematurely during cyclic loading. In addition, extensive crack analysis from DIC imaging as well as analysis of fiber strain data has demonstrated the different behaviour of flexion and shear cracks. In addition it could be shown that the shear of reinforcement bars in pure bending zones due to the eccentric position is not at all negligible.

Le béton textile est un nouveau matériau à haute performance composé d’une matrice cimentaire et d’une armature en fibres synthétique. L’état des connaissances est encore trop peu avancé pour une utilisation à grande échelle mais les nouvelles opportunités offertes par ce matériau sont telles qu’il est nécessaire de les compléter. Le béton textile offre d’une part de nouvelles possibilités architecturales grâce à sa flexibilité et sa finesse et d’autre part pourrait aider à diminuer l’empreinte écologique du domaine de la construction en utilisant moins de ciment et en construisant des structures plus durables. Dans ce projet, on veut à la fois mettre en valeur le matériau et tester ses limites en construisant un abri soumis à des charges importantes et ayant une forme telle que seul le béton textile soit intéressant pour la réaliser. On en profitera pour explorer différentes méthodes de construction en béton textile en faisant varier le mortier et les techniques de coffrage. Dans un premier temps, on conçoit la forme et les dimensions principales puis on construit la coque avant de la tester. En parallèle, on réalise des tests pour caractériser les matériaux utilisés et à partir de ces résultats on construit un modèle éléments finis ainsi qu’un modèle de résistance à la flexion composée. Sur la base de ces deux modèles, on vérifie le dimensionnement de la structure effectué et conçoit un agrandissement de la coque en multipliant sa taille par trois.

Le viaduc de Polcevera (Viadotto Polcevera, nom officiel en italien) est un ouvrage d'art sur l'autoroute italienne A10 permettant la traversée du val de Polcevera dans la ville de Gênes. Le viaduc, d'une longueur totale d'un peu plus d'un kilomètre, franchit la rivière Polcevera ainsi que deux importants parcs ferroviaires et des zones construites. Il a été conçu par l'ingénieur italien Riccardo Morandi, ce qui lui donne le nom plus populaire de Pont Morandi. La construction du pont a été réalisée entre les années 1963 et 1967. Il a été inauguré le 4 septembre 1967 par Giuseppe Saragat, président de la République italienne à cette époque. Le 14 août 2018, une partie du viaduc s'effondre, faisant 43 morts et 16 blessés. Une longueur d'environ 245 mètres de tablier est détruite ainsi que le pylône 9. Cette catastrophe implique donc la mise hors service de l'ouvrage et plonge la ville de Gênes dans une situation chaotique.

Traditionally, the concrete strength is measured on cubes or cylinders having normalized dimensions, suitable vibration and curing conditions and their strength is assessed in laboratory under fast loading rates. However, the in-situ strength of structural elements can considerably differ from that of a small and homogenous control specimen due to a number of issues. Notably, phenomena taking place during the consolidation process of fresh concrete may affect the compressive resistance of tall members as well as the bond strength of reinforcing bars located in top layers. During concrete consolidation, water migrates in the direction of the free surface while concrete settles downwards, phenomena referred as concrete bleeding and plastic settlement respectively. Under these circumstances, a decrease in the concrete properties near the upper surface is observed as well as a development of cracks and voids surrounding horizontal reinforcing bars, causing potential disturbances on the compressive stresses and affecting the mechanical engagement between bars and concrete. In addition, the response of structural concrete may differ from that of material samples due to non-uniform stress states, the material brittleness, the cracking induced by imposed strains, the rheological response of concrete and the presence of embedded disturbances. As a result, the strength measured in material samples needs to be corrected with strength reduction factors to ensure suitable structural analysis. In this thesis, an in-depth investigation is performed on the different phenomena affecting the compressive and bond strength of structural members. These aspects are assessed by means of several testing programmes instrumented with refined measurements techniques such as tomography and Digital Image Correlation. An extensive experimental programme comprising 76 column and prism tests was carried out to evaluate the influence of casting position, loading direction and bar disturbances on the compressive resistance of structural elements. The detailed measurements performed at the fresh and hardened state resulted in the proposal of consistent design rules accounting for the investigated phenomena. Focus was also given on the influence of material brittleness and the implications of internal stress redistributions on the structural response of reinforced concrete columns and compression zones of members in bending. The pertinence of the investigations were validated based on more than 400 column tests collected from the literature. The implications of casting conditions on pull-out and spalling failures were also assessed by means of 137 pull-out tests on reinforcing bars presenting variable diameter, concrete cover, casting height and embedded length. The investigations resulted in the proposal for a physically-consistent approach, evaluating the pull-out resistance as function of casting conditions and reinforcement characteristics. Finally, the phenomenon of cover spalling was examined with respect to the action of a radial inner pressure, as originated by bond engagement or associated to the volumetric expansion of corroded reinforcement. The mechanisms inducing spalling were analysed by means of a comprehensive experimental programme comprising 56 specimens instrumented with Digital Image Correlation. A mechanical model is eventually proposed to evaluate bond-related cases of cover spalling.

Punching shear reinforcement is an efficient method to increase not only the strength but also the deformation capacity of flat slabs supported by columns. Especially, the increase in deformation capacity is desired so that the load can be distributed to other supports preventing a total collapse of the structure in the case of the occurrence of a local failure. Thus, the research presented herein addresses the punching strength as well as the deformation capacity of flat slabs. Thereby, the focus is set on the analysis of the maximum increase in strength and rotation capacity due to punching shear reinforcement. Therefore, the principal aim is the analysis of flat slabs with large amounts of punching shear reinforcement. In addition to an experimental and numerical investigation of flat slabs, another principal objective of the research project was the development of an analytical model that enables accurate predictions of the punching strength and the rotation capacity of flat slabs with large amounts of shear reinforcement. Thus, the research presented herein can basically be divided into three main parts. An experimental investigation of sixteen flat slab specimens with and without shear reinforcement leads to new findings with respect to the punching strength and the load-deformation response of flat slabs. The results of the tests serve for the validation of current design codes and the Critical Shear Crack Theory. In addition to the specimens tested within this research project, tests found in literature are used to investigate the influence of certain parameters on the prediction of the punching strength. A non-linear numerical model on the basis of the Finite Element Method enables the modeling of the test specimens. This approach uses plane stress fields to calculate the moment-curvature response of a discrete slab element. The thereby obtained flexural and torsional stiffness serve as input parameters for a linear-elastic finite element analysis. This analysis enables the modeling of the load-deformation response of the tested slab specimens leading to valuable information regarding the state of deformation at different load levels. The findings of the experimental and the numerical investigation support the development of an analytical model. The theoretical background of this model is the Critical Shear Crack Theory, which describes the punching strength as a function of the slab rotation. Thus, the developed analytical model enables the calculation of the load-rotation response of flat slab specimens. Moreover, the developed failure criteria enable the prediction of the punching strength as well as the maximum rotation capacity. Finally, it is shown that the results obtained from the developed model are in good agreement with results of tests performed within this research project and of tests found in literature.

The present research represents a theoretical and experimental contribution to the understanding of the structural behaviour of elements made of ultra-high performance fibre-reinforced concrete (UHPFRC). UHPFRC is investigated as an advanced cementitious material offering particular potential in innovative bridge design. The optimised material composition results in high compressive strength and non-negligible tensile strength and ductility, provided by multi-microcracking. This allows significant tensile forces to be sustained by elements in bending even without the use of ordinary reinforcement. Thanks also to the material's resistance to environmental degradation, very thin structural elements can be constructed. This research focuses primarily on the bending behaviour and design of thin UHPFRC beams and slabs. Punching-shear is also investigated as a possible failure mode of thin UHPFRC slabs. One of the main differences between other concretes and UHPFRC is that the latter requires mechanical models capable of taking tensile behaviour into account for rational structural application. Analytical and numerical models are developed in this study to simulate the non-linear bending response of UHPFRC beams and slabs. This permits the assessment of element behaviour at service states and prediction of failure loads. Theoretical research on both bending and punching-shear failure is supported by experimental research on beams and slabs made of BSI® UHPFRC with 2.5 % volume of 20-mm long steel fibres. The analytical model for beams in bending takes both material multi-microcracking and macrocrack propagation with tensile softening into consideration. Multi-microcracking is modelled as a pseudo-plastic tensile behaviour, while the macrocrack is simulated based on the assumptions of the fictitious crack model. The results are in good agreement with experimental data and simulations obtained from a developed finite element model. Using theoretical results and experimental data it is demonstrated that pre-peak behaviour and bending strength are mainly governed by multi-microcracking. The propagation of the macrocrack provides only a minor additional contribution to bending strength, but, in the case of thin beams, plays an important role in providing ductility in bending. Theoretical results demonstrate that, due to the presence of pronounced pseudo-plastic deformations, size effect on bending strength is much less significant for UHPFRC than for other quasi-brittle materials, which corresponds to experimental observations. It is however shown that, even if the pseudo-plastic phase is less pronounced, thin elements develop behaviour similar to that of elements with high pseudo-plastic tensile deformations, owing to the low stress decrease in tensile softening. Nonetheless, in the absence of pseudo-plastic tensile deformations, the behaviour of thick elements approaches that of typical quasi-brittle materials, with a more pronounced size effect. In the case of thin statically indeterminate beams and slabs, it is shown that a high level of tensile ductility can allow sufficient internal force redistribution to occur, leading to a significant increase in load-bearing capacity. Moreover, high rotations can be sustained after cracking while almost constant bending strength is maintained, resulting in a plastic-like behaviour. It is demonstrated that the theory of plasticity can thus be applied: a formulation is proposed to predict the resistant plastic moment, enabling easy estimation of the bending failure load for thin elements. The analysis results show good agreement with test results for slabs of different thicknesses. However, due to the remarkable size effect on ductility in bending, the rotation capacity of UHPFRC elements thicker than approximately 100 mm is limited, and the theory of plasticity does not apply. Experimental and theoretical research on the punching-shear failure of thin UHPFRC slabs demonstrates the influence of structural parameters on achieved shear resistance. A proposal is made for considering fibre contribution in shear resistance as a structure-dependent parameter, relating the critical shear crack opening to slab rotation. This approach results in more accurate predictions for thin elements with larger deformations as compared to current code predictions that overestimate resistances for such elements. With a view to the structural application of UHPFRC in bridge design, the concept of ribbed deck slab is studied. Based on the theoretical and experimental results it is demonstrated that thin UHPFRC slabs (40-60 mm) without ordinary reinforcement can be effectively used in this concept: sufficient bending and punching-shear resistances to locally applied traffic loads can be ensured. With prestressed ribs, UHPFRC ribbed slabs attain high load-bearing capacity, while structural dead weight is significantly decreased. This concept could open up new vistas in the design of new structures and offers effective possibilities for the structural repair or widening of existing bridges.

Le projet de Master prévoit la conception et le dimensionnement d’un pont submergé dans le lac Léman qui permettra de connecter les villes de Lausanne et Genève avec un système de transport à haute vitesse du type MAGLEV. Ce genre de structure représente une alternative performante aux ponts traditionnelles pour le franchissement des surfaces d’eau grâce à l’exploitation d’une ouvrage complétement submergé situé à une profondeur fixe. La solution proposé est composée entièrement de modules préfabriqués en béton armé précontrainte liée monolithiquement ensemble sur place. Le tunnel est réalisé avec 199 éléments cylindrique de ϕ=14.5m et 190m de longueur disposé sur un nombre équivalent de pile avec une configuration structurelle typique des ponts a joint Gerber. Les piles, d’hauteur variable entre 7.5 et 45m, ont une section cylindrique de ϕ=6.0m qui est élargis en tête pour accueillir les appareilles mécaniques d’appuis. Un système de 20 pieux battue ouvert en acier assure la transmission des actions au sol de fondation. Les pièces du pont sont conçues pour avoir une certaine capacité de flottage nécessaire pour les opérations de remorquage. Cette aptitude est réglable à travers deux compartiments de ballast disposé dans le caisson qui permet soit de submergé les pièces que de régler les charges gravitaires pour qu’elles soient parfaitement en équilibre avec la poussée d’Archimède lors de la phase de service. Le tracé du pont se développe principalement le long de la côte du lac à profondeur fixe d’environ 30m. Cette alignement permet de réduire considérablement les actions hydrodynamiques et environnementales tous en garantissant des profondeurs contenues qui facilite les opérations de mise en oeuvre. Le concept structurel proposé peut être certainement adapté pour d’autres projet de ce type.

Aggregate interlocking is a phenomenon occurring when the opposite sides of a concrete crack slide relative to each other. Due to surface roughness, protruding material from one crack-side can engage with the opposite one and thus exchange forces. This affects the load-carrying capacity for structures where the failure is determined by the development of large cracks, like beams and slabs without transverse reinforcement. In such cases, aggregate interlocking contributes significantly to the various shear-transfer actions, allowing forces to traverse cracks. Aggregate interlocking has been studied for several decades, leading to various experimental and theoretical approaches. However, a number of aspects remain unclear, like the development of new cracks from the initial one and the influence of certain concrete properties on the interlocking forces (e.g. aggregates, crack surface roughness). The present research project comprises three scientific publications focusing on the fundamentals of interlocking and force transfer across concrete cracks and other interfaces related to concrete structures. It is based on the results of an extensive experimental campaign performed with an arrangement allowing to apply precise kinematics upon material discontinuities. The tested specimens include pre-cracked concrete prisms subjected to simultaneous crack opening and sliding and steel-to-concrete interfaces characterized by simple geometries (spheres and rebar-surfaces). Particular attention is given to the roughness properties of the tested cracks and interfaces, several of which were scanned at high resolution. The experimental results are used to develop a new model for estimating aggregate interlocking forces as a function of crack kinematics. The model is based on the approach originally introduced by Li and Maekawa (1987) with the Contact Density Model and allows estimating the contact properties using 2D crack-profiles. Depending on the crack width, two contributions to force transfer are considered. For contacts occurring in wide cracks, contact forces are calculated using an elastic-plastic material law, whereas for small crack opening the effect of residual material soundness is considered. The model can be applied on surfaces corresponding to tests with various failure modes, thus considering different levels of roughness. Finally, the bond between steel rebar-ribs and concrete is investigated using steel-to-concrete interface specimens, and several similarities with aggregate interlocking are discussed. The previously introduced model is extended to the case of interlocking rebar-ribs, where it can estimate the bond and confinement stresses and the decrease in bond strength for cases where cracks develop parallel to the rebars. The thesis ends with an extensive appendix containing details on the performed tests which can be of interest for future researchers.

Le projet du terminal de Southampton situé dans la ville du Havre propose une réactivation et régénération du secteur économique et touristique normand, mis en difficulté après la crise des années 2008 à 2014. Le port, endroit stratégique situé sur le front de mer et le sud de la ville, n'avait pas survécu à la Seconde Guerre mondiale, et c'est dans cette zone de reconstruction d'après-guerre que s’insère le projet. L'énoncé théorique « Havre délire » a été l’occasion d’effectuer un rapprochement audacieux entre une vision quasi paranoïaque de la ville de Rem Koolhaas, développée dans son manifeste "New York délire", et la ville du Havre, véritable manifeste du classicisme structurel d’Auguste Perret. Le projet de diplôme tente quant à lui, d'incarner et donner forme aux fruits de cette union. Ainsi, le projet résulte de la tension entre la vague de mer Normande, libre et fugace, qui tente d'échapper au diktat de la grille structurelle en béton armé, brut de décoffrage. Si chaque plateforme constitue un maillage rigide de poutres métalliques, profil HEA 220, les espaces, eux, échappent à la simple compréhension du plan, coupe et élévation.

En las losas soportadas por apoyos puntuales y en aquellas que están sometidas a importantes cargas concentradas, así como en zapatas y en otras estructuras superficiales, es necesario verificar la resistencia frente a esfuerzo cortante alrededor del soporte o de las cargas concentradas, ya que frecuentemente ésta es la condición que determina el espesor de la losa o la zapata y también las dimensiones de los soportes o los capiteles. Este fenómeno se conoce como punzonamiento. La rotura por punzonamiento en losas sin armadura de cortante se produce de manera frágil, por lo cual es particularmente indeseable y conviene prestarle gran atención tanto en la concepción como en la ejecución. De manera frecuente, la presencia de pilares de borde y esquina es elevada y su proporción respecto a las columnas interiores es grande. Es por ello que resulta necesaria una buena comprensión del fenómeno del punzonamiento en este tipo de estructuras. El punzonamiento en losas es uno de los problemas más estudiados en las estructuras de hormigón, pese a ello, resulta ser todavía parcialmente desconocido y carece de una unificación en su tratamiento. El dimensionamiento basado en la verificación de un esfuerzo cortante nominal (medido sobre un perímetro llamado crítico) comparado con una resistencia obtenida por métodos empíricos, se impone en casi todas las normativas debido a su simplicidad. Los ensayos muestran que otros parámetros como la cuantía de armadura, el tamaño de árido o el efecto escala tienen también influencia sobre la resistencia nominal. Los objetivos de esta tesina son contribuir a la comprensión del punzonamiento en losas de hormigón armado sin armadura de punzonamiento sobre pilares de borde y esquina, comparar la predicción de las diferentes normas respecto a diversas series de ensayos recogidas en la literatura y verificar el buen comportamiento de la teoría de la fisura crítica. El cálculo de la resistencia al punzonamiento según la teoría de la fisura crítica se basa en un criterio de rotura por el cual la resistencia al punzonamiento VR es inversamente proporcional a la rotación de la losa ψ alrededor del pilar. Cuanto mayor es la rotación de la losa, menor es su resistencia al punzonamiento. O expresado de otra forma, cuanto más rígida es la losa a flexión, más resistirá al punzonamiento. Para determinar la resistencia al punzonamiento de una losa con ayuda del criterio de rotura, es necesario establecer la curva de comportamiento Carga V - Rotación ψ de la losa. Las características de rigidez de la losa definen esta relación V - ψ. La resistencia VR queda definida como la ordenada del punto de intersección entre el criterio de rotura y el comportamiento en flexión de la losa. 3 Los resultados derivados del estudio realizado muestran un mejor comportamiento de la nueva norma suiza (SIA 262-2010) comparado con las otras normas estudiadas, debido principalmente a que se fundamenta en un modelo físico como es la teoría de la fisura crítica y no en modelos empíricos. En general los resultados obtenidos con el Eurocódigo 2 son también satisfactorios, pero en ocasiones se obtiene gran dispersión y por tanto menor fiabilidad. La norma americana ACI 318 resulta ser siempre la más conservadora, obteniéndose también mucha dispersión sobre todo para pilares de esquina. Esta tesina ha sido realizada en el marco de una línea de investigación desarrollada en el departamento de estructuras de hormigón (IBETON) de la École Polytechnique Fédérale de Lausanne, bajo la supervisión de Luca Tassinari y la dirección de Aurelio Muttoni.