京都大学 / 新制・課程博士 / 博士(農学) / 甲第23528号 / 農博第2475号 / 新制||農||1087(附属図書館) / 学位論文||R3||N5359(農学部図書室) / 京都大学大学院農学研究科地域環境科学専攻 / (主査)教授 藤原 正幸, 教授 中村 公人, 准教授 藤澤 和謙 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DGAM

O problema de como descrever a dinâmica efetiva de partículas ou campos confinados a um espaço-tempo de baixa dimensão é de interesse em muitas áreas da física. Vários métodos foram propostos na literatura para atacar este problema. Recentemente, foram relatadas algumas evidências experimentais que são consistentes com a chamada abordagem de potencial confinante. À luz destes resultados, o objetivo desta tese é o de construir uma teoria quântica para partículas confinadas em uma subvariedade, imersa em um espaço-tempo plano, empregando o cenário conceitual da abordagem de potencial confinante. A tese está dividida em duas partes. A primeira parte é dedicada exclusivamente ao estudo da mecânica quântica em uma subvariedade. Para esta finalidade, deduzimos as equações efetivas de Schrödinger, Dirac e Klein-Gordon, em uma subvariedade curva, na presença de um campo electromagnético externo. Examinamos as características singulares estas equações e apresentamos algumas aplicações em física da matéria condensada. Na segunda parte, partimos da mecânica quântica na subvariedade e então formulamos a teoria quântica de campos (TQC) na subvariedade. Mostramos que a TQC \"livre\" em uma subvariedade pode ser representada esquematicamente como uma teoria de campos livres, em um fundo curvo, mais um potencial escalar e um campo externo SO(n - m) de Yang-Mills. Calculamos para essa teoria a ação efetiva em ordem de um laço para bósons e férmions a temperatura e potencial químico não nulos, em todas as ordens, usando a expansão de Seely-DeWitt. Para teorias com interações, demonstramos que a teoria conhecida como eletrodinâmica quântica reduzida (RQEDd?,de) pode ser recuperada a partir da abordagem de potencial confinante. Para uma teoria bidimensional, propomos uma grande classe de extensões do modelo de Schwinger, em que a interação entre férmions vai além do potencial linear. Demonstramos que, notavelmente, essas extensões são exatamente solúveis para férmions sem massa e que não há geração de massa dinâmica para os férmions. Além disso, construímos uma nova família de teorias que podem ser exatamente bosonizadas. Também mostramos que RQED4,2 tem as características necessárias para ser identificada como uma teoria de campo efetivo para fios de grafeno. Finalmente, estudamos o efeito da interação de campos magnéticos e pseudomagnéticos no grafeno. Para este sistema, calculamos o condensado fermiônico, a densidade de carga induzida de vácuo, a ação efetiva em ordem de um laço e a magnetização. Demonstramos que a presença de um campo pseudo-magnético diferente de zero torna possível observar experimentalmente uma densidade de carga induzida de vácuo. Além disso, vamos mostrar que é possível ter controle sobre a magnetização, bem como a massa dinâmica para cada vale no grafeno, quer seja por deformações ou variando o campo magnético aplicado. / The problem of how to describe the effective dynamics of particles or fields confined to a lower dimensional curved space-time is of interest in many areas of physics. In the literature, several methods have been proposed to attack this problem. Recently it has been reported some experimental evidences that are consistent with the so-called confining potential approach. In light of these results, the purpose of this thesis is to construct a quantum theory for particles confined in a submanifold of a flat space-time employing the theoretical framework of the confining potential approach. The thesis is divided into two parts. The first one is dedicated exclusively to the study of quantum mechanics on a submanifold. For this purpose, we derive the effective Schrödinger, Dirac and Klein-Gordon equations on a curved submanifold, in the presence of an external electromagnetic field. We examine the singular features of these equations and present some applications to condensed matter. In the second part of this thesis, we start from the quantum mechanics on the submanifold and then we formulate the quantum field theory (QFT) on the submanifold. We will show that the \"free\" QFT on a submanifold can be schematically represented as a quantum theory of free fields on a curved background plus a scalar potential and an external SO(n-m) Yang-Mills field. For this theory, we compute the one-loop effective action for scalars and fermions at finite temperature and chemical potential to all orders using the Seely-DeWitt expansion. For interacting theories, we will prove that the theory known as reduced quantum electrodynamics (RQEDd?,de) can be recovered from the confining potential approach. For a two-dimensional theory, we propose a large class of extensions of the Schwinger model, in which the interaction between fermions goes beyond the linear potential. We demonstrate that, remarkably, these extensions are exactly solvable for massless fermions and that there is no dynamical mass generation for the fermions. Furthermore, we construct a new family of exactly bosonized theories. We also show that RQED4,2 has the necessary features to be identified as an effective field theory for graphene wires. Finally, we study the effect of an interplay of real and pseudomagnetic fields in graphene. We compute the fermion condensate, the induced vacuum charge density, the one-loop effective action and the magnetization, for this system. We will show that the presence of a non-zero pseudomagnetic field makes it possible, experimentally, to observe an induced vacuum charge density. Moreover, we will show that it is possible to have control over the magnetization as well as the dynamical mass for each valley in graphene, by straining or varying the applied magnetic field.

Despite advancements in the analysis of statnamic load testing data, there exists uncertainty with underlying procedural assumptions. Two such assumptions are that the system mass and soil-related damping coefficient remain constant throughout the loading event. These assumptions are the culprit of aberrant predictions of the static capacity at small displacements when the overall displacement is large. An exploration of the assumptions may validate prior existing test results as well as solidify the current analysis process. However, an exploration could also reveal an overestimation or underestimation of portions of the predicted static load responses. The testing program outlined herein consists of a two-phase sequential agenda devoted toward the preparation and familiarization of a new laboratory statnamic device. The first phase involves the development of user guidelines for accurately targeting a desired statnamic test, and the second incorporates the guidelines into a preliminary testing regime specifically targeted at determining a suspected strain-dependant statnamic damping coefficient. The steps taken in this thesis are intended to launch future research endeavors toward obtaining a better understanding of the statnamic damping coefficient.

O problema de como descrever a dinâmica efetiva de partículas ou campos confinados a um espaço-tempo de baixa dimensão é de interesse em muitas áreas da física. Vários métodos foram propostos na literatura para atacar este problema. Recentemente, foram relatadas algumas evidências experimentais que são consistentes com a chamada abordagem de potencial confinante. À luz destes resultados, o objetivo desta tese é o de construir uma teoria quântica para partículas confinadas em uma subvariedade, imersa em um espaço-tempo plano, empregando o cenário conceitual da abordagem de potencial confinante. A tese está dividida em duas partes. A primeira parte é dedicada exclusivamente ao estudo da mecânica quântica em uma subvariedade. Para esta finalidade, deduzimos as equações efetivas de Schrödinger, Dirac e Klein-Gordon, em uma subvariedade curva, na presença de um campo electromagnético externo. Examinamos as características singulares estas equações e apresentamos algumas aplicações em física da matéria condensada. Na segunda parte, partimos da mecânica quântica na subvariedade e então formulamos a teoria quântica de campos (TQC) na subvariedade. Mostramos que a TQC \"livre\" em uma subvariedade pode ser representada esquematicamente como uma teoria de campos livres, em um fundo curvo, mais um potencial escalar e um campo externo SO(n - m) de Yang-Mills. Calculamos para essa teoria a ação efetiva em ordem de um laço para bósons e férmions a temperatura e potencial químico não nulos, em todas as ordens, usando a expansão de Seely-DeWitt. Para teorias com interações, demonstramos que a teoria conhecida como eletrodinâmica quântica reduzida (RQEDd?,de) pode ser recuperada a partir da abordagem de potencial confinante. Para uma teoria bidimensional, propomos uma grande classe de extensões do modelo de Schwinger, em que a interação entre férmions vai além do potencial linear. Demonstramos que, notavelmente, essas extensões são exatamente solúveis para férmions sem massa e que não há geração de massa dinâmica para os férmions. Além disso, construímos uma nova família de teorias que podem ser exatamente bosonizadas. Também mostramos que RQED4,2 tem as características necessárias para ser identificada como uma teoria de campo efetivo para fios de grafeno. Finalmente, estudamos o efeito da interação de campos magnéticos e pseudomagnéticos no grafeno. Para este sistema, calculamos o condensado fermiônico, a densidade de carga induzida de vácuo, a ação efetiva em ordem de um laço e a magnetização. Demonstramos que a presença de um campo pseudo-magnético diferente de zero torna possível observar experimentalmente uma densidade de carga induzida de vácuo. Além disso, vamos mostrar que é possível ter controle sobre a magnetização, bem como a massa dinâmica para cada vale no grafeno, quer seja por deformações ou variando o campo magnético aplicado. / The problem of how to describe the effective dynamics of particles or fields confined to a lower dimensional curved space-time is of interest in many areas of physics. In the literature, several methods have been proposed to attack this problem. Recently it has been reported some experimental evidences that are consistent with the so-called confining potential approach. In light of these results, the purpose of this thesis is to construct a quantum theory for particles confined in a submanifold of a flat space-time employing the theoretical framework of the confining potential approach. The thesis is divided into two parts. The first one is dedicated exclusively to the study of quantum mechanics on a submanifold. For this purpose, we derive the effective Schrödinger, Dirac and Klein-Gordon equations on a curved submanifold, in the presence of an external electromagnetic field. We examine the singular features of these equations and present some applications to condensed matter. In the second part of this thesis, we start from the quantum mechanics on the submanifold and then we formulate the quantum field theory (QFT) on the submanifold. We will show that the \"free\" QFT on a submanifold can be schematically represented as a quantum theory of free fields on a curved background plus a scalar potential and an external SO(n-m) Yang-Mills field. For this theory, we compute the one-loop effective action for scalars and fermions at finite temperature and chemical potential to all orders using the Seely-DeWitt expansion. For interacting theories, we will prove that the theory known as reduced quantum electrodynamics (RQEDd?,de) can be recovered from the confining potential approach. For a two-dimensional theory, we propose a large class of extensions of the Schwinger model, in which the interaction between fermions goes beyond the linear potential. We demonstrate that, remarkably, these extensions are exactly solvable for massless fermions and that there is no dynamical mass generation for the fermions. Furthermore, we construct a new family of exactly bosonized theories. We also show that RQED4,2 has the necessary features to be identified as an effective field theory for graphene wires. Finally, we study the effect of an interplay of real and pseudomagnetic fields in graphene. We compute the fermion condensate, the induced vacuum charge density, the one-loop effective action and the magnetization, for this system. We will show that the presence of a non-zero pseudomagnetic field makes it possible, experimentally, to observe an induced vacuum charge density. Moreover, we will show that it is possible to have control over the magnetization as well as the dynamical mass for each valley in graphene, by straining or varying the applied magnetic field.

Sublevel caving (SLC) is a mass mining method relying on the flowability of the blasted material. The ore is blasted in slices against caved material which is mainly waste rock. The result of the confined blast is greatly influenced by the interaction between the blasted material and the caved material. During blasting both materials change characteristics; the blasted material increases its porosity and compressibility due to breakage and swelling while the caved material is compacted and decreases in porosity and compressibility. The understanding of the mechanisms involved in this process is of significant importance. The behavior of the caved material (confining material) was studied in laboratory under dynamic loading. A new apparatus was developed to conduct impact tests to simulate blasting conditions. The tested material was a blend of crushed waste rock from drift development in the Kiirunavaara mine with maximum particle size 32 mm. The material was tested for two conditions, i.e. dry and wet (pendular state), and with different impact velocities (low (5 m/s), medium (8 m/s) and high (10-12 m/s)). During the impact tests, two types of measurements were taken; dynamic measurements based on the recordings from the installed accelerometers on the machine and static measurements pre- and post-impact. Additionally, the angle of repose, the impact duration, and the fragmentation was measured. In addition to the laboratory tests, small-scale blasting tests were carried out to investigate the burden behavior in confined conditions. The blasted specimen was a cuboid magnetic mortar block and the confining material was crushed concrete with maximum particle size 16 mm. The blocks were instrumented with custom-made incremental displacement sensor. After the analysis of the results from the above experimental work, two confined pillar tests (test #1 and test #2) were carried out at the Kiirunavaara mine. The preparation work for the pillar tests involved the development of instrumentation and installation techniques. The experimental configuration contained two blastholes and measurement holes in between the blastholes drilled from the neighboring drift. Test #1 mainly focused on the evaluation of the instrumentation and techniques while test #2 was focused on the interaction between the blasted burden and the confining material. The confining material in test #1 was a blend of ore and waste material from drift development at the Kiirunavaara mine. The characteristics of the material were unknown. Test #2 was split into two parts, the confining material in the first part was the same as in the laboratory impact tests and the second part of the pillar was confined by caved masses. The instrumentation was installed in the burden of the pillars and was equipped with accelerometers and displacement sensor. Additional instrumentation was also installed in the confining material. The burden in the small-scale blasting tests reached maximum velocity 29 m/s and maximum displacement 12.6 mm. In pillar tests, the burden movement was in the range of 0.9 to 1.1 m. In both pillar tests, burden erosion material was observed in the gap between the intact and the blasted burden. This material was finer compared to the blasted burden. The origin of this material was from the vicinity of the blastholes. The results of the laboratory tests showed that the wet material exhibited larger compaction zone than that of the dry material. The wet material showed apparent cohesion close to the impact surface of the tested material. A similar observation was made in test #2 where an agglomeration of the confining material, as a result of apparent cohesion, was observed on the surface of the blasted burden. The displacement data from the instrumentation in the burden and inside the confining material showed that the compaction zone follows an inverse exponential behavior. After the blast steeper angles of repose were measured indicating higher frictional forces between the particles. Moreover, the evidence of apparent cohesion and a larger angle of repose indicated the introduction of tensile strength in the material. The mass of the confining material was compressed elastically and plastically during the blast. After the blast, the material recovered its elastic deformation and pushed the blasted burden backward as observed in the small-scale blasting tests and the pillar tests. At this stage, the burden erosion material was compacted. Hence, there were 3 materials, i.e. burden erosion material, burden and confining material, which were compacted with different compaction rates. This condition promotes interlocking of the particles in the materials. If this behavior is correlated with a production SLC ring, then it indicates disturbances in flowability of the blasted material.

No description available.

Ce travail de thèse concerne la prédiction des structures en béton soumises à des chargements extrêmes. Il s'intéresse plus particulièrement au comportement du béton sous fort confinement où la contrainte peut atteindre des niveaux de l'ordre du giga Pascal. La modélisation de ce comportement doit être capable de reproduire la compaction irréversible. Pour ce faire, deux lois de comportement élasto-plastique - endommageable ont été développées et implantées dans un code aux éléments discrets. Les paramètres utilisés dans ces lois sont calibrés par les simulations des essais de traction/compression uniaxial, des essais hydrostatiques et triaxiaux. Une fois les paramètres calibrés, la loi montrant le meilleur agrément avec l'expérience a été choisie pour la prédiction de la réponse du béton sous différents niveaux de confinement. Les résultats du modèle sont analysés non seulement à l'échelle macroscopique mais également à l'échelle de l'élément discret. La nécessité de prendre en compte une loi d'interaction de type élasto-plastique-endommageable est aussi montrée. La deuxième partie du travail de thèse développe une méthode de couplage entre le modèle éléments discrets et un modèle d'écoulement compressible en tenant compte des mécanismes physiques fondamentaux d'interaction entre l'écoulement interne et les particules solides d'un matériau poreux. Le problème d'écoulement est résolu par une méthode en volumes finis, où le volume est discrétisé en tétraèdres issus d'une triangulation régulière de Delaunay. Notre modèle est une adaptation aux fluides compressibles d'un modèle développé initialement pour les écoulements incompressibles. Ce couplage a été utilisé pour simuler le comportement triaxial des bétons humides et saturés sous différents niveaux de confinement. Les résultats nous montrent une bonne reproduction du comportement non-drainé du béton saturé sous faible confinement. Pour fort confinement, les simulations ne se rapprochent des résultats expérimentaux qu'au prix d'une compressibilité du fluide plus faible que celle de l'eau. Par ailleurs, la contrainte effective était une variable pertinente pour décrire le comportement du béton humide par un état limite intrinsèque indépendant du degré de saturation. / This thesis work deals with the predicting of concrete structures submitted to some extreme loadings, and, more particularly, focuses on behavior of concrete under a high-confining pressure. At this range of pressures, irreversible compaction of the material occurs and needs to be considered. Doing so, two elasto-plastic-damaged constitutive laws have been developed and implanted into a discrete element numerical code. Local parameters to be used in these constitutive laws are identified by simulating reference uniaxial traction/compression tests and triaxial compression tests. Once these parameters have been obtained, the law showing the best agreement with the experimental data has been chosen to predict the reponse of concrete sample for triaxial compressive tests at different levels of confinement. The numerical results have been analyzed not only at macroscopic scale but also at discrete element scale. The need of a constitutive law taking into account the elasto-plastic-damaged behavior has been also proved. The second objective of the thesis work was to develop a fluid flow – coupled discrete element model by considering fundamental physical mechanisms of the interaction between the internal fluide flow and the solid particles of a porous material. The flow problem is solved by the finite volume method, where the volume is discretized into tetrahedra issue of a regular Delaunay triangulation. Our model is an adaptation for elastic fluids of a model originally developed for incompressible flows. The developed fluid-flow coupled discrete element has been used to simulate the undrained triaxial behavior of concrete under different levels of confinement. The results show a good reproduction of undrained behavior of saturated concrete under low confinement. For high confinement, the simulations only resemble the experimental results when the fluid compressibility is lower than that of water. Moreover, the effective stress was a relevant variable to describe the behavior of the wet concrete by an intrinsic limit state independent of the degree of saturation.

Ce mémoire de thèse est consacré au développement de nouveaux systèmes catalytiques dérivés de métallocyclodextrines. Les travaux qui y sont décrits ont trait à la mise au point de méthodes de fonctionnalisation régiosélective de la face primaire des cyclodextrines donnant accès à des ligands hétérodentés de type P,P’ à chiralité inhérente. Ces derniers forment quantitativement des complexes chélate de géométrie cis, dont les versions rhodiées ont été testées en hydrogénation eten hydroformylation asymétriques d’oléfines prochirales. L’étude des propriétés complexantes et catalytiques de deux phosphines confinantes dérivées d’α- et de β-cyclodextrine a également étér éalisée. L’ancrage rigide de l’atome de phosphore (III) au sein de la matrice cyclodextrine permet de confiner le centre métallique au coeur du macrocycle, ce qui se traduit par la formation exclusive de complexes mono-ligandés en phosphore. Les complexes monophosphine de rhodium (I) catalysent l’hydroformylation asymétrique du styrène avec une très forte sélectivité en produit branché et une énantiosélectivité très élevée. Le pontage de diaminocyclodextrines par l'acénaphtènequinone permet d’obtenir des ligands potentiellement confinants dans lesquels l’anse azotée de type N-(2-N’-alkylaminoacenaphthenyl)alkylimine est dissymétrique. L’oxydation du pont par voie chimique ou électrochimique conduit à une anse imidazole 1,2-disubstitué très courte qui provoque une forte déformation du squelette cyclodextrine. / This manuscript is concerned with the design of novel catalytic systems derived from metallocyclodextrins. The first part describes new ways of functionalising the cyclodextrin primary face regioselectively for accessing inherently chiral P,P’ chelators. These heterodentate ligands gavequantitatively cis-chelate complexes with various d8 cations. Their rhodium(I) complexes were assessed in the asymmetric hydrogenation and hydroformylation of prochiral olefins. Thecoordination and catalytic properties of two phosphines derived from a- and b-cyclodextrin are also reported. With their phosphorus lone pair pointing toward the CD core, these confining ligands force the coordinated metal centre to stay within the CD hollow and promote the formation of singly phosphorus-ligated complexes. Rhodium (I) monophosphine complexes of this type catalyse the asymmetric hydroformylation of styrene with both very high isoselectivity and enantioselectivity. Capping of diaminocyclodextrins with acenaphthenequinone resulted in the formation of a nonsymmetricN-(2-N’-alkylaminoacenaphthenyl)alkylimine handle with two intra-annular nitrogen atoms. A strong deformation of the cyclodextrin scaffold was shown to take place upon chemical or electrochemical oxidation of the bridging unit into the very short 1,2-disubstituted imidazole moiety.

Il est couramment admis que la déformation plastique des phases MAX est dueau glissement de dislocations dans les plans de base s'organisant en empilements et murs. Cesderniers peuvent former des zones de désorientation locale appelées kink bands. Cependant, lesmécanismes élémentaires et le rôle exact des défauts microstructuraux sont encore mal connus. Cemanuscrit présente une étude expérimentale multi-échelle des mécanismes de déformation de laphase MAX Ti2AlN. A l'échelle macroscopique, deux types d'expériences ont été menés. Des essaisde compression in-situ à température et pression ambiantes couplés à la diffraction neutroniqueont permis de mieux comprendre le comportement des différentes familles de grains dans le Ti2AlNpolycristallin. Des essais de compression sous pression de confinement ont également été réalisés dela température ambiante jusqu'à 900 °C. À l'échelle mésoscopique, les microstructures des surfacesdéformées ont été observées par MEB et AFM. Ces observations complétées par des essais denanoindentation ont montré que la forme des grains et leur orientation par rapport à la directionde sollicitation gouvernent l'apparition de déformations intra- et inter-granulaires ainsi que lalocalisation de la plasticité. Finalement à l'échelle microscopique, une étude détaillée par METdes échantillons déformés sous pression de confinement a révélé la présence de configurations dedislocations inédites dans les phases MAX, telles que des réactions entre dislocations, des dipôleset des dislocations hors plan de base. À la vue de ces résultats nouveaux, les propriétés mécaniquesdes phases MAX sont rediscutées. / It is commonly believed that plastic deformation mechanisms of MAX phases consistin basal dislocation glide, thus forming pile-ups and walls. The latter can form local disorientationareas, known as kink bands. Nevertheless, the elementary mechanisms and the exact role ofmicrostructural defects are not fully understood yet. This thesis report presents a multi-scale experimentalstudy of deformation mechanisms of the Ti2AlN MAX phase. At the macroscopic scale,two kinds of experiments were performed. In-situ compression tests at room temperature coupledwith neutron diffraction brought new insight into the deformation behavior of the different grainfamilies in the polycrystalline Ti2AlN. Compression tests from the room temperature to 900 °Cunder confining pressure were also performed. At the mesoscopic scale, deformed surface microstructureswere observed by SEM and AFM. These observations associated with nanoindentationtests showed that grain shape and orientation relative to the stress direction control formationof intra- and inter- granular strains and plasticity localization. Finally, at the microscopic scale,a detailed dislocation study of samples deformed under confining pressure revealed the presenceof dislocation configurations never observed before in MAX phases, such as dislocation reactions,dislocation dipoles and out-of-basal plane dislocations. In the light of these new results, mechanicalproperties of MAX phases are discussed.

La recherche présentée dans cette thèse vise à examiner le mécanisme d’écaillage des bétons exposés au feu et comprendre l’influence du chargement mécanique appliqué en compression durant le chauffage. Des cubes (200 x 200 x 200 mm3) et des dalles (800 x 800 x 100 mm3) de béton fabriqués avec des ciments CEM II et CEM III (B40-II et B40-III: fc28days ≈ 40 MPa) ont été exposés à un feu ISO 834-1 sous différents niveaux de chargement uniaxial (cubes) et biaxial (dalles). En outre, l'effet du chargement mécanique (pression de confinement et charge uniaxiale) sur la perméabilité résiduelle au gaz a été étudié. Afin de mieux analyser les résultats expérimentaux et comprendre les mécanismes à l’origine de l'écaillage, des calculs numériques ont été réalisés en utilisant un modèle thermo-mécanique du code aux éléments finis CAST3M. Les résultats expérimentaux ont clairement montré que les éprouvettes chargées (uniaxial et biaxial) présentent un risque d’écaillage plus important que les éprouvettes non chargées. L’écaillage augmente avec le niveau de contrainte appliquée. Une partie des essais mais pas tous, ont montré que le B40-II (3% de laitier) présente un écaillage plus important que celui du béton B40-III (43% de laitiers).À partir de cette étude sur deux bétons ordinaires, il peut être mis en évidence qu'un certain niveau de contrainte de compression externe (uniaxiale ou biaxiale) est nécessaire pour induire l'écaillage du béton ordinaire. Les pressions des pores se combine avec les contraintes thermiques dûes aux gradients thermiques. Les contraintes de compression appliquées empêchent la création de certaines fissures générées par l'incompatibilité des déformations thermiques de la pâte de ciment et des granulats et des gradients thermiques. Pour l'échantillon non chargé, la création de fissures augmente la perméabilité et empêche naturellement le développement des pressions de pores.Pendant un feu réel, les membres structurels en béton sont toujours chargés ou retenus. La présence d'un chargement compressif pendant le chauffage augmente considérablement le stress de compression (diminue le stress de traction) et la grandeur de la pression des pores, ce qui augmente le risque d'écaillage. Ensuite, le stress compressif appliqué est un facteur clé très important que la conception de la résistance au feu des structures en béton devrait prendre en compte lors de l'écaillage. Par conséquent, il est recommandé que les essais d'écaillage ne soient pas effectués uniquement sur des échantillons non chargés. / The research presented in this thesis seeks to examine and understand the mechanism of fire spalling role played by the external compressive loading during heating. Concrete cube (200 x 200 x 200 mm3) and slab (800 x 800 x 100 mm3) specimens made with CEM II and CEM III cements (B40-II and B40-III: fc28days ≈ 40 MPa) were exposed to ISO 834-1 fire curve under different levels of external uniaxial (for cube) and biaxial (for slab) compressive stress. Additionally, the effect of external compressive loading (confining pressure and uniaxial load) on the residual gas permeability of concretes have been investigated. In order to better analyse the experimental results and to provide more insight into the mechanism behind the fire spalling behaviour of concrete, numerical computations were carried out by using the existing thermo-mechanical model implemented in a finite element code CAST3M. The experimental results have clearly shown that the loaded specimens (uniaxial and biaxial) are more prone to spalling than unloaded specimens, with increasing amounts of spalling for higher values of applied compressive stress. Part of the tests, but not all have shown that B40-II (3% of slag) exhibited higher spalling than the B40-III (43% of slag).From this study on two ordinary concretes, it highlights that a certain level of external compressive stress (uniaxial or biaxial) was necessary to induce spalling. A possibility is that the applied compressive stress prevents the creation of cracks naturally due to thermal mismatch between cement paste and aggregates and thermal gradients. For unloaded specimen, the creation of cracks increases the permeability and naturally prevents the pore pressure to exceed a value that favours spalling.During a real fire, concrete structural members are always loaded or restrained. The presence of compressive loading during heating significantly increases the compressive stress (decreases the tensile stress) and the magnitude of pore pressure, which increase the risk of fire spalling. Then, the applied compressive stress is a very important key factor that the fire resistance design of concrete structures should take into account when considering spalling. Hence, it is recommended that the fire spalling test should not be carried out only on unloaded specimens, especially for the ordinary concrete.