The behaviour of reinforced concrete flat plate structures, subjected to various combinations of vertical and horizontal loads, was studied. Being mainly experimental, the investigation consisted of (i) The development and the design of the instrumentation systems to obtain the appropriate information; (ii) the observation of the behaviour at various stages and under various load combinations, and (iii) the evaluation of the experimental data which resulted in a suggestion for a method of analysis applicable to the design of structures of this particular type. Two large scale test structures, consisting of a 21 ft. x 21 ft. and 4 in. thick plate supported on nine columns spaced at 10 ft. centres, were designed, instrumented and tested. The studies of the behaviour of these two test structures concentrated on two main aspects of the problem: i. The general flexural behaviour of the test structure, under various load combinations, ii, The local behaviour of various types of slab-column connections, with particular reference to the punching shear strength problem. For both of the above aspects, various methods of analysis are applied; and compared with the experimental findings. A number of conclusions are drawn from these comparisons as well as from the observations. Some suggestions are also made for further research on the subject.

The behaviour of slab column junction of reinforced concrete flat slab structures, subjected to various combinations of vertical load and moment, was studied. Two different failure modes were investigated, (i) Shear failure. (ii)Flexural failure. The theoretical approach of the shear failure based on the equilibrium of the internal forces in a slab and the compatibility of the deformation of the concrete and steel. The failure criteria is assumed to be the failure of a concrete cone under biaxial compression in the compressive zone at the vicinity of the column faces. The analysis of the flexural failure was achieved by studying the yield line patterns and using the virtual work method. The theoretical method of analysis was applied for internal columns and extended to the case of external columns. To fill in the gap of available experimental data ten square slabs of 5 ft. side lengths and three circular slabs of 5 ft, diameter, and 4 in. thick simply supported along the edges were specially designed and tested under different combinations of axial load and bending moment. The proposed analysis is applied to these slab tests and a comparison between the observed and predicted failure loads is presented. The theoretical analysis is applied to all other available slab tests and compared with the experimental findings. Good agreement is obtained between the test and calculated loads. A number of conclusions are drawn from these comparisons as well as from the experimental observations. Some suggestions are also made for further research on the subject.

The results of an experimental and theoretical investigation into the behaviour of reinforced concrete flat slab-column connections are presented. In the experimental programme 33 lightweight and 8 normal weight slabs were failed in punching shear. The specimens were simply supported and loaded vertically through central, monolithic column stubs. Three lightweight aggregates were used, and the concrete strength and section depth varied. It was found that slabs made with Lytag, Solite and limestone aggregates failed at similar loads, but slabs made with Leca aggregate concrete failed at approximately 70% of the former group (other variables being equal). In the theoretical investigation an analysis was developed to model the various stages of the slabs' behaviour under increasing load. The analysis enabled the critical pre-failure and punching loads to be calculated. Satisfactory agreement was established between the pre-failure values. The load at which failure occurred in the compression zone was computed using one of two methods designed to accommodate the differing characteristics of the concretes used. The methods depend on an idealisation of the behaviour of the shear crack which enables the compression zone stresses to be. established. Comparison of these stresses with a criterion of failure gives the concrete failure load. The ultimate punching load includes the enhancing effects, on the concrete failure load, of inplane stresses and dowel action. Good agreement between the theoretical, and. experimental punching values was established. The thesis includes a review of previous experimental and analytical work performed on normal and lightweight aggregate slabs. The existing empirical data is shown to be limited in several areas, especially for lightweight aggregate concrete tests. The application of existing formulae to the present experimental work does not provide a satisfactory agreement with the results. Three of the equations axe re-evaluated to pr6vide a closer fit with the present test results and for a wider based group of lightweight aggregate tests. The provisions of ACI 318-71 and CP. 110 : 1972 are also applied to the slabs of the present test series, and are shown to be conservative. Finally recommendations for future work are given.

This thesis includes an experimental investigation of the behaviour of steel fibre reinforced high performance concrete (SFRHPC) under biaxial loading conditions. Also included are constitutive models to enable numerical predictions of the strength behaviour of such a material. Within the experimental stage a large biaxial test machine was designed and manufactured. The load capacity of each axis was 2000 kN. Special thought was given to the load platen system because of the friction which occurs between the platen system and the concrete specimen. Brush bearing platens and solid steel blocks with and without Teflon friction reducing pads were tried. Because the brush platen and the Teflon pads were constantly damaged during testing, solid steel block platens were finally used. For tests where tension loads were involved, experiments were carried out with dog-bone shaped specimens and specimens glued on to the platens. Finally, the tension loads were transferred through threaded rods cast into the specimens and connected to the machine patterns with screws. Modern control schemes and high speed data acquisition systems were used to monitor the material response and to collect experimental stress and strain results. The principal deformations were monitored and the crack patterns and failure modes examined. Failure envelopes were developed based on the strength data for each fibre variable. The load capacity of SFRHPC under biaxial load conditions was found to be larger than for plain HPC for all fibre types and volume fractions. The stress-strain recordings indicated a linear behaviour almost up to failure. The examined failure mode between plain and steel fibre HPC was similar and all specimens failed very suddenly with a splitting failure type. The test variables included four different types of hooked ended steel fibres with different fibre volume fractions from plain to 2% in 0.5% steps. The specimens were tested under the entire range of stress combinations including uniaxial compression and tension and biaxial compression-compression and compression-tension. As a result the specimen still failed in an explosive manner but the pieces were still connected together by fibres after failure. The biaxial strength compared to the uniaxial strength increased more, as observed with normal strength concrete. With the addition of fibres the biaxial strength behaviour of HPC was almost the same as for plain normal strength concrete. The deformation characteristics of plain and SFRHPC showed a linear behaviour up to a higher stress than normal strength concrete. In fact the linear limit was almost as high as the failure load. The examined strength data was used to model the biaxial strength envelopes of HPC and SFRHPC using different methods. These included the Ottosen failure criterion and the Willam and Warnke failure criterion.

Experiments were carried out to study: a) the parameters which influence the efficiency and quality of remote robotic hydroerosion for removing defective concrete, b) the flexural behaviour of 6 different types of generic repair materials, c) the water permeability of the above 6 types of generic repair materials, and d) the parameters which influence the adhesive strength of patch repairs. In order to evaluate the efficiency and quality of remote robotic hydroerosion, 4 sets of parameters (concrete, pressure, generating unit, demolishing unit and nozzle parameters) were investigated using 7 series of tests. The flexural behaviour of 6 different types of generic repair materials was investigated by performing 160 flexural tests on solid, unrepaired and repaired beam specimens. The water permeability of the above 6 different types of repair materials was investigated by using ISAT and absorption by immersion tests on 100x100x100 mm cubes. Finally, 4 parameters (type of substrate surface, strength of substrate, type of repair material and use of bonding/agent primer), which influence the mode of failure and value of the adhesive strength of patch repairs were investigated by performing 300 pull-off tests. In the experimental study, fringe-based laser interferometry was used to measure and characterise the roughness of concrete substrates prior to repair. Results obtained using the above method proved the ability of remote robotic hydroerosion to produce surfaces with higher roughness values which in turn promote the adhesive strength between concrete substrates and repair materials.

The present research is concerned with investigating the structural effect of using steel fibre-reinforcement on the punching shear behaviour of ground-suspended slabs with internal columns. The main objectives of this research were to develop a constitutive model for steel fibre-reinforcement (SFRC), to study experimentally the punching shear behaviour of SFRC with no longitudinal reinforcement and to develop a finite element model that can accurately predict the behaviour of SFRC slabs subjected to punching shear. In this respect, a literature review of the work undertaken by previous researchers on punching shear behaviour of concrete slabs is presented. After that, a constitutive model for SFRC was developed. This is followed by a preliminary finite element analysis (FEA) and experimental study of SFRC slabs. Finally, a finite element model was developed. The literature review revealed that little work has been carried out to study the effect of fibre-reinforcement on the punching shear capacity of concrete slabs. Furthermore, structures, hence a thorough investigation in this area was mandatory. A constitutive model for SFRC in post-cracking stage was developed. This enables one to estimate the tension stiffening behaviour of SFRC based on a simple beam bending test and a statistical model developed in this research, this constitutive model was used later on in the modelling of the SFRC slabs using FEA. In the preliminary FEA, sufficient information for the size and the design of test specimens that were used in the experimental programme was produced. In the experimental study, eight steel fibre-reinforced concrete slab-column connection specimens were tested. The variables of the test specimens include the concrete compressive strength, fibre dosage and fibre aspect-ration.

Η εργασία αυτή αποτελείται από επτά κεφάλαια: Στο Πρώτο κεφάλαιο γίνεται μια πρώτη γνωριμία με τα Ινοπλέγματα Ανόργανης Μήτρας. Συγκεκριμένα γίνεται αναφορά στις ιδιότητες και είδη των υλικών που συνθέτουν τα παρα-πάνω στοιχεία. Στη συνέχεια στο Δεύτερο κεφάλαιο γίνεται μια παρουσίαση των έως τώρα εφαρμογών των στοιχείων ΙΑΜ. Το Τρίτο κεφάλαιο πραγματεύεται την παρουσίαση των βασικών μηχανισμών λειτουργίας των λεπτότοιχων στοιχείων ΙΑΜ έναντι διαφόρων εντατικών καταστάσεων. Επίσης παρου-σιάζονται και εξισώσεις σχεδιασμού που δίδονται από την διεθνή βιβλιογραφία. Στο Τέταρτο κεφάλαιο παρουσιάζεται μια βιβλιογραφική ανασκόπηση που έχει ως στόχο την κατανόηση της λειτουργίας των σύμμικτων στοιχείων που αποτελούνται από σύνθετα υλικά και σκυρόδεμα. Στην βιβλιογραφική ανασκόπηση παρουσιάζονται εργασίες που ασχο-λούνται με την διερεύνηση της συμπεριφοράς: • Συστημάτων ενίσχυσης στοιχείων με ΙΑΜ, • Παραμενόντων τύπων από Ινοπλισμένα Πολυμερή • Παραμενόντων τύπων από Ινοπλέγματα Ανόργανης Μήτρας. Στο Πέμπτο κεφάλαιο γίνεται η παρουσίαση της πειραματικής μεθοδολογίας που ακολου-θήθηκε, ενώ στα κεφάλαια έξι και επτά γίνεται η παρουσίαση των πειραματικών αποτελε-σμάτων και των συμπερασμάτων που εξήχθησαν από αυτά αντίστοιχα. / -

Cette thèse de doctorat est réalisée en partenariat avec EDF et s’inscrit dans le cadre de la gestion du parc de tours aéroréfrigérantes des centrales nucléaires. Certaines tours présentent des fissures qui peuvent favoriser la carbonatation du béton d’enrobage et ainsi accélérer l’initiation de la corrosion des armatures. L’objectif de ce travail est de caractériser l’impact de ces fissures sur l’initiation et la propagation de la corrosion des armatures. Un programme expérimental dédié est détaillé. Dans un premier temps, un protocole de fissuration permettant de reproduire les fissures observées sur les tours est défini. Une attention particulière a été portée à la limitation de l’endommagement de l’interface acier/béton. Les éprouvettes fissurées sont ensuite carbonatées (de manière accélérée) dans le double but de mesurer la longueur de la zone d’interface altérée et de dépassiver l’armature en fond de fissure pour permettre l’initiation de la corrosion. La corrosion est contrôlée en laboratoire par l’intermédiaire de cycles de pluie/séchage et l’état de corrosion est caractérisé par différentes techniques (desquamation, microscopie optique, spectroscopie Raman, suivi de potentiel de corrosion libre). Différentes configurations représentatives du service des tours aéroréfrigérantes sont testées (3 ouvertures de fissures, 2 orientations de fissures, température, HR, etc.). Les résultats obtenus permettent de montrer qu’après une période d’initiation, la vitesse moyenne de corrosion décroit rapidement et que l’acier tend à se repassiver. Cette repassivation est liée à la formation d’une couche d’oxydes en fond de fissure qui limite l’accès de l’oxygène et de l’eau à l’armature. / This thesis is performed in partnership with EDF in the framework of concrete ageing management of cooling towers of Electricity of France (EDF) nuclear power plants. Indeed some of them can be affected by cracks which may promote the carbonation of the concrete cover and accelerate the reinforcement corrosion initiation. The objective of this work is to characterize the impact of these cracks on the initiation and propagation of reinforcement corrosion. A dedicated experimental program is detailed. Firstly, a cracking protocol reproducing cracks found in the concrete of cooling towers is defined. Particular attention was paid to limit the damage along the steel/mortar interface. Cracked specimens are thereafter exposed to accelerated carbonation for the dual purpose of measuring the length of the damaged interface and accelerating the depassivation of the rebar deep in the crack in order to accelerate the corrosion initiation. The corrosion is controlled in the laboratory via raining/drying cycles and its state is characterized by several technics (desquamation, optical microscopy, Raman spectroscopy, monitoring of the free corrosion potential). Different configurations representative of the cooling towers are tested (three crack openings, 2 crack orientations, temperature, relative humidity, etc.). Obtained results show that after the corrosion initiation period, the corrosion kinetics decreases rapidly and the reinforcement tends to repassivation. This repassivation is related to the formation of oxide layer deep in the crack limiting therefore the access of water and oxygen to the rebar.

Cette thèse s’intéresse à l’étude l’effet de la corrosion sur les propriétés mécaniques des armatures corrodées et les performances mécaniques résiduelles des poutres corrodées. L’étude est basée sur deux poutres corrodées notées B2CL2 et B2CL3, conservées respectivement 26 ans et 28 ans en ambiance saline. Deux poutres non corrodées B2T2 et B2T3 conservées en conditions ambiantes ont également été testés afin d’identifier l'effet de la corrosion indépendamment du vieillissement.Les propriétés mécaniques des armatures corrodées ont été étudiées par des essais de traction.La limite d'élasticité et résistance à la rupture ont été étudiées sur la base de la section transversale résiduelle évaluée par perte de masse. Les résultats ont montré que les effets de la corrosion sur la diminution ductilité étaient très importants. La forme de la section transversale résiduelle apparait comme étant un paramètre essentiel affectant la ductilité de l'armature.Les performances résiduelles en flexion des poutres corrodées ont été étudiées. Les résultats montrent que la corrosion réduit la capacité portante et de façon plus significative, la flèche maximale à rupture en raison d’un changement de mode de rupture. La diminution de la charge de plasticité apparait en relation avec la perte de section d’acier tendu due à la corrosion Des poutres de portées courtes ont été réalisées à partir des poutres corrodées après les essais de flexion. Les tests mécaniques ont été effectués en flexion pour vérifier la réponse des poutres courtes corrodées. Les poutres courtes corrodées ont péri en flexion avec une bonne ductilité tandis que les poutres courtes non corrodées ont péri comme prévu en cisaillement suivant un mode de rupture fragile, qui a montré que la corrosion de l'armature pouvait modifier les modes de défaillance.Les produits de corrosion ont été recueillis à partir de l'armature corrodée de B2Cl3. Des expériences XRD et TG ont été menées afin d'identifier la composition des produits de corrosion. Le coefficient d'expansion des produits de corrosion a été déduit, ce qui pourrait être utile pour les recherches futures concernant le mécanisme de fissuration du béton d'enrobage. / The thesis aims to study the influence of chloride corrosion on the mechanical properties ofthe reinforcement and RC beams. The experiments were based on two corroded beams named B2Cl2 and B2Cl3, with a corroded age of 26 years and 28 years respectively. Two noncorroded beams B2T2 and B2T3 which were cast in the same condition and same time were also tested in order to make clear the corrosion effect.The mechanical properties of the corroded reinforcement were investigated by the tensiontests. The yield strength and ultimate strength were studied based on the residual gravimetrical cross-section. The results found that the impact of corrosion on the ductility was more significant than that of the strength. The shape of residual cross-section was considered to be in deep relationships with the ductility of the reinforcement.The flexural performances of the beams were studied. The results showed that the corrosion deteriorated the capacity and the ductility of the corroded beams. The corrosion degree of reinforcement was found in linear with the residual yield capacity of the corroded beams.The short-span beams were formed from the corroded beams after bending tests. Mechanical tests were carried out directly to check the response of the corroded beams. The corroded short-span beams failed in bending mode with good ductility while the non-corroded beams performed a brittle shear failure mode, which showed that the corrosion of reinforcement could change the failure modes.The corrosion products were collected from the corroded reinforcement of B2Cl3. XRD andTG experiments were conducted so as to identify the composition of the corrosion products.The expansive coefficient of the corrosion products was deduced, which could be helpful forthe further research on the cracking mechanism of the concrete cover

Les objectifs de la thèse sont d’étudier l’influence de la pré-fissuration sur le développement de la corrosion des armatures du béton armé, les corrélations entre les pertes de section d’armatures dues à la corrosion et la fissuration du béton d’enrobage en résultant et l'effet de la corrosion sur les propriétés mécaniques des structures en béton armé soumis à un environnement salin. Les essais ont été réalisées pour étudier les différentes propriétés mécaniques comme la résistance à la flexion, la résistance au cisaillement, etc. Le travail expérimental est constitué de deux parties: dans la première partie des petits échantillons annulaires en mortier ont été testés afin d'observer l'effet des fissures sur la corrosion. Les résultats montrent que quelque soit l’ouverture des fissures, la corrosion démarre en fond de fissure et se propage le long de l’interface acier-béton endommagée en fond de fissure par la création de la fissure. Dans la deuxième partie, une étude approfondie a été réalisée sur une poutre en béton armé qui a été corrodée dans un environnement salin pendant 26 ans et une poutre non corrodée de même âge pour mieux comprendre l'effet de la corrosion sur les propriétés mécaniques (flexion, cisaillement , propriétés mécaniques de l’acier corrodé) d’éléments en béton armé. Un nouveau modèle a été proposé pour la relation entre la largeur des fissures de corrosion et la perte de section d'acier / The thesis aims to study the effect of corrosion on the mechanical properties of reinforced concrete reinforced concrete structures in chloride environment. Experiments were carried out in order to investigate the different mechanical properties such as bending strength, shear strength etc. The experimental work consists of two parts; in the first part small annular cement sand mortar samples were tested in order to observe the effect of cracks on corrosion. Results show that cracks whatever their width allows the corrosion onset at bottom of cracks and along the steel-concrete interface damaged zone caused by the creation of cracks. In the second part an extensive study was carried out on a 26-year-old corroded reinforced concrete beam and a non-corroded of same age in order to better understand the effect of corrosion on reinforced concrete members in flexion and shear. Impact of corrosion on the mechanical properties of steel in reinforced concrete was studied. A new model was proposed for the relationship between corrosion cracks width and loss of steel cross-section