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Connolly, Raymond J. "The spalling of concrete in fires." Thesis, Aston University, 1995. http://publications.aston.ac.uk/14310/.
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The occurrence of spalling is a major factor in determining the fire resistance of concrete constructions. The apparently random occurrence of spalling has limited the development and application of fire resistance modelling for concrete structures. This Thesis describes an experimental investigation into the spalling of concrete on exposure to elevated temperatures. It has been shown that spalling may be categorised into four distinct types, aggregate spalling, corner spalling, surface spalling and explosive spalling. Aggregate spalling has been found to be a form of shear failure of aggregates local to the heated surface. The susceptibility of any particular concrete to aggregate spalling can be quantified from parameters which include the coefficients of thermal expansion of both the aggregate and the surrounding mortar, the size and thermal diffusivity of the aggregate and the rate of heating. Corner spalling, which is particularly significant for the fire resistance of concrete columns, is a result of concrete losing its tensile strength at elevated temperatures. Surface spalling is the result of excessive pore pressures within heated concrete. An empirical model has been developed to allow quantification of the pore pressures and a material failure model proposed. The dominant parameters are rate of heating, pore saturation and concrete permeability. Surface spalling may be alleviated by limiting pore pressure development and a number of methods to this end have been evaluated. Explosive spalling involves the catastrophic failure of a concrete element and may be caused by either of two distinct mechanisms. In the first instance, excessive pore pressures can cause explosive spalling, although the effect is limited principally to unloaded or relatively small specimens. A second cause of explosive spalling is where the superimposition of thermally induced stresses on applied load stresses exceed the concrete's strength.
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Jansson, Robert. "Fire Spalling of Concrete : Theoretical and Experimental Studies." Doctoral thesis, KTH, Betongbyggnad, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-128378.
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Fire spalling of concrete is not a new phenomenon. To some degree there has always been a risk during rapid heating of concrete. Therefore, to a certain degree the effect of fire spalling is included in the bank of data from fire tests and fires on which our understanding of the fire resistance of concrete is based. However, the development and modern use of more dense concrete mixes have produced cases of very severe fire spalling which have increased the urgency to understand this phenomenon. In this context, the use of an addition of polypropylene (PP) fibres to the mix to limit the amount of spalling has been one topic of interest for this thesis. During fire tests on a post-tensioned concrete structure made of spalling sensitive concrete, it has been shown that substantially lower amounts of PP fibres than 2 kg/m3, which is recommended in the Eurocode (1992-1-2:2004), can be used with successful results. As part of this study, another important aspect has emerged, i.e. the impact the test method used can have on the fire spalling depths observed in concrete specimens. This has been known for many years but is seldom discussed in the scientific literature. In this thesis it has been shown that results from tests on unloaded cubes do not necessarily correspond to results seen on larger loaded slabs. In the results presented, none of the tested cubes spalled whereas some of the large slabs spalled to the degree that the reinforcement became fire exposed. Further, the difference in spalling depths between small and large post-tensioned slabs was shown to be substantial; although in general the ranking in severity from least to greatest spalling correlated between these two specimen sizes. The correlation to larger specimens was much vaguer in the case when the small slabs were not loaded in compression as there sometimes was no spalling in the small slabs. From time to time the randomness of the fire spalling of concrete has been mentioned. To investigate this further, an analysis of 110 fire tests performed on small slab type specimens was performed. This analyse showed that the spalling behaviour had a good repeatability between two identical tests, which proved that the so called “random factor” relating to spalling depth was low for the chosen data set. It was also possible to make a multiple least squares fit of test parameters that could be used to predict the spalling behaviour which also underlines that a substantial stochastic factor was not present. Regarding the influence of different factors, the results compiled on the influence of ageing show that for three of the tested Self-Compacting Concrete (SCC) mixes, the amount of spalling was reduced with age whereas for the fourth mix (which included the highest amount of limestone filler, 140 kg/m3) the spalling was not reduced with age. In this test series no systematic influence of the intensity of the fire, between standard fire exposure and the more severe hydrocarbon fire, on the spalling depth was detected for this type of specimen. The only major difference was that spalling started earlier during the more severe fire exposure. Pressure measurements conducted as part of the work within this thesis, supported by results from the literature, indicate that there is no relationship between pressure rise due to moisture and fire spalling. Based on this and the fact that the spalling event in many cases happens at relatively low temperatures where the saturation vapour pressure is low two alternative factors to explain the function of PP fibres have been presented: (i) PP fibres reduce the moisture content in the critical zone close to the heated surface which affects the mechanical properties advantageously, and (ii) PP fibres amplify moisture movement leading to larger drying creep and shrinkage which locally relax the thermal stresses. To investigate the influence of the presence of moisture on the compressive strength, specimens were tested after being boiled for varying periods of time in a water bath. The study showed a remarkable reduction of strength due to boiling of the mortar specimens. After boiling mortar in a water bath for 3, 10 or 20 minutes, i.e. approximately the same time span as the initiation of fire spalling during fully developed fires, the strength was only 64% of the corresponding value for a dry specimen. As no strength change was detected between the specimens boiled 3, 10 or 20 minutes, and that the corresponding saturation pressure for steam at 100ºC is negligible compared with the tensile strength of concrete, it was concluded that pore pressure is not a significant contributor to the measured reduction in strength. It appears that the presence of moisture itself rather than an increased pressure is the most important factor reducing strength. This is a clear indication that moisture plays a key role in the fire spalling of concrete but in a different way from previously assumed.QC 20130911
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Jansson, Robert. "Material properties related to fire spalling of concrete /." Lund : Division of Building Materials, Lund Institute of Technology, Lund University, 2008. http://www.byggnadsmaterial.lth.se/.
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Thiruchelvam, Chellathurai. "Deterioration and spalling of high strength concrete at elevated temperatures." Thesis, City University London, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.274476.
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Yanko, William Andrew. "Experimental and numerical evaluation of concrete spalling during extreme thermal loading." [Gainesville, Fla.] : University of Florida, 2004. http://purl.fcla.edu/fcla/etd/UFE0006380.
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Khalid, Nibras Nizar. "STRENGTH REDUCTION OF REINFORCED CONCRETE COLUMNS SUBJECTED TO CORROSION RELATED COVER SPALLING." University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron152536559529405.
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Khoylou, Naysan. "Modelling of moisture migration and spalling behaviour in non-uniformly heated concrete." Thesis, Imperial College London, 1997. http://hdl.handle.net/10044/1/7317.
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Busba, Ezeddin Rafaa. "Effect of Localized Corrosion of Steel on Chloride-Induced Concrete Cover Cracking in Reinforced Concrete Structures." Scholar Commons, 2013. http://scholarcommons.usf.edu/etd/4872.
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Abstract: Concrete cover cracking due to reinforcement corrosion is widely accepted as a limit-state indicator in defining the end of functional service life for existing reinforced concrete (RC) structures undergoing corrosion. Many of the currently available durability prediction models are incapable of providing realistic estimates of remaining service lives of RC structures beyond the corrosion initiation point. Therefore, the need to incorporate the length of the corrosion propagation stage in a comprehensive durability prediction approach has recently received much research attention. Previous research focus however was mostly limited to the case of uniformly corroding reinforcement with only few studies addressing the commonly encountered case of localized rebar corrosion. It was empirically shown in a previous study that localized corrosion can have a mitigating effect on time to concrete cover cracking due to the larger required depth of rebar corrosion penetration (Critical penetration or Xcrit). The present research was focused on developing a model for predicting Xcrit for various degrees of corrosion localization including new cases of highly localized corrosion. Accelerated corrosion testing of controlled anodic regions along axial rebars in sound concrete cylinders suggested that localized corrosion can increase Xcrit by up to about a factor of 10. The effect of corrosion localization on the orientation of corrosion-induced surface cracks was also addressed. Testing of freely corroding pre-cracked RC pipe specimens in a chloride-containing environment indicated that steel corrosion can be localized at intersection regions with the pre-existing cracks and uniformly distributed around the reinforcing steel perimeter. Numerical modeling was undertaken to substantiate the experimentally observed trends on a theoretical basis for various degrees of corrosion localization. A mechanical model was developed to improve understanding of the underlying mechanism responsible for corrosion-induced stresses. A thick-walled multiple-cylinder approach was employed to simulate crack initiation and propagation to account for the residual strength property of concrete after cracking by applying the principles of applied elasticity. For a given concrete cover depth, the amount of Xcrit was shown by modeling to be largely determined by the length of corroding region and the capacity of the induced cracks to accommodate produced rusts. The properties of both concrete-rebar interface and corrosion products were also found to have a significant impact on Xcrit. Based on the model and experimental trends and comparisons with literature data, an improved relationship for the estimation of Xcrit was proposed. An electrochemical model was also formulated to address the possible role of corrosion aggravation due to macrocell coupling in counteracting the mitigating effect of increased Xcrit on time to concrete cover cracking. Findings confirmed that corrosion localization can reasonably be considered a mitigating factor for extending the corrosion propagation stage, and provided more precise quantification to that effect.
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Khalaf, Jamal. "Development of non-linear bond stress-slip models for reinforced concrete structures in fire." Thesis, Brunel University, 2017. http://bura.brunel.ac.uk/handle/2438/14863.
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Exposure of concrete structures to high temperatures leads to significant losses in mechanical and physical properties of concrete and steel reinforcement as well as the bond characteristics between them. Degradation of bond properties in fire may significantly influence the load capacity of concrete structures. Therefore the bond behaviours need to be considered for the structural fire engineering design of reinforced concrete structures. At present, the information about the material degradations of concrete and reinforcing steel bars at elevated temperatures are generally available. However, the research on the response of the bond characteristic between concrete and reinforcing steel bar at elevated temperatures is still limited. Due to the lack of robust models for considering the influence of the bond characteristics between the concrete and steel bar at elevated temperatures, the majority of the numerical models developed for predicting the behaviour of reinforced concrete structures in fire was based on the full bond interaction. Hence, the main purpose of this research is to develop robust numerical models for predicting the bond-slip between concrete and the reinforcement under fire conditions. Therefore, the bond-slip between the concrete and reinforcement for conventional and prestress concrete structures at both ambient and elevated temperatures has been investigated in this research. Two models have been developed in this study: the first model is to simulate the behaviour of bond-slip of deformed steel bars in normal concrete at room temperature and under fire conditions. The model is established based on a partly cracked thick-wall cylinder theory and the smeared cracking approach is adopted to consider the softening behaviour of concrete in tension. The model is able to consider a number of parameters: such as different concrete properties and covers, different steel bar diameters and geometries. The proposed model has been incorporated into the Vulcan program for 3D analysis of reinforced concrete structures in fire. The second robust model has been developed to predict the bond stress-slip relationship between the strand and concrete of prestressed concrete structural members. In this model, two bond-slip curves have been proposed to represent the bond-slip characteristics for the three-wire and seven-wire strands. This model considers the variation of concrete properties, strands’ geometries and the type of strand surface (smooth or indented). The degradation of materials and bond characteristic at elevated temperatures are also included in the model. The proposed models have been validated against previous experimental results at both ambient and elevated temperatures and good agreements have been achieved. A comprehensive parametric study has been carried out in this research to examine the influence of bond-slip model on the structural behaviours of normal reinforced concrete structures. The study investigated the most important factors that can affect the bond characteristics between concrete and steel reinforcement at elevated temperatures. These factors are: the concrete cover, spalling of concrete, concrete compressive and tensile strengths.
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Miah, Md Jihad. "The effect of compressive loading and cement type on the fire spalling behaviour of concrete." Thesis, Pau, 2017. http://www.theses.fr/2017PAUU3015/document.
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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 chargésThe 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
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Dauti, Dorjan. "A combined experimental and numerical approach to spalling of high-performance concrete due to fire." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAI062/document.
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Le béton est un matériau très utilisé dans l'industrie de construction. Une limite essentielle à un usage de ce matériau est sa dégradation par écaillage lorsqu’il est exposé au feu. Le phénomène d'écaillage consiste en une éjection du béton sous forme d'écailles à la surface du béton exposée à l'incendie. La section de béton s'en trouve progressivement réduite. De plus, ce phénomène expose les armatures et peut conduire à une rupture prématurée de structures telles que les tunnels, les gratte-ciels, les centrales nucléaires etc. De nombreuses recherches ont été consacrées à la mise au point de méthodes de prévention de l'écaillage et à la détermination des paramètres qui ont une influence sur ce phénomène. Cependant, la physique qui contrôle l'écaillage n'est pas encore entièrement comprise. L'objectif principal de la thèse est de fournir une meilleure compréhension des mécanismes impliqués dans l’écaillage du béton en utilisant une approche numérique-expérimentale, i.e., la tomographie neutronique couplée à la modélisation numérique avancée à une échelle adéquate.Dans ce travail, les premières mesures 3D de la teneur en eau du béton (grandeur locale indispensable au suivi du processus de déshydratation potentiellement responsable de l’écaillage) soumis à un chargement thermique sévère ont été réalisées à l'aide de tomographies neutroniques rapides. Le suivi de la déshydratation rapide du béton a été possible en réalisant un scan 3D toutes les minutes grâce à la source neutrons de l'Institut Laue Langevin (leader mondial), à Grenoble, France. Cette vitesse d'acquisition est dix fois plus rapide que toute autre étude tomographique rapportée dans la littérature. Un dispositif, adapté à l'imagerie neutronique et aux essais à haute température, a été développé pour réaliser de telles expériences. L'influence de la taille des agrégats sur la distribution de l'humidité au sein de l'échantillon est présentée. Les résultats quantitatifs sur l'accumulation d'humidité derrière le front de déshydratation, connue sous le nom de 'moisture-clog" et considérée comme un des facteurs principaux engendrant un excès de pression, sont également présentés et discutésEn parallèle, un modèle thermo-hydro-mécanique (THM) entièrement couplé a été mis en œuvre sur le logiciel élément fini Cast3M afin d'étudier et prédire le comportement du béton à haute température. Le code nouvellement implémenté est remarquablement plus rapide (20-30 fois) que le code existant sur lequel il est basé. Une approche mésoscopique a été adaptée au modèle pour prendre en compte l'hétérogénéité du béton. D'abord, le modèle est appliqué à des expériences de la littérature, qui étu-dient les paramètres standards tels que la température, la pression du gaz et la perte de masse. En-suite, des profils d'humidité 1D obtenus à partir d'expériences de radiographie neutronique sont utili-sés pour vérifier et améliorer le modèle en termes de lois de comportement critiques telles que les courbes de déshydratation et de rétention d'eau. Enfin, le modèle est utilisé pour prédire la distribution d'humidité 3D mesurée dans ce travail de doctorat par tomographie neutronique. Entre autres, des simulations THM mésoscopiques sont effectuées pour étudier l'influence d'un agrégat sur le front de séchageConcrete has been extensively used in the construction industry as a building material. A major drawback of this material is its instability at high temperature, expressed in the form of violent or non-violent detachment of layers or pieces of concrete from the surface of a structural element. This phenomenon, known as fire spalling, can lead to the failure of concrete structures such as tunnels, high rise buildings, nuclear power-plants, underground parkings etc. because the reinforcement steel is directly exposed to high temperature and the designed cross section of the concrete elements (e.g., columns, beams, slabs) is reduced. A lot of research has been dedicated on developing preventing methods for spalling and also on determining the parameters that have an influence on it. However, the physics behind this phenomenon is not yet fully understood.In this doctoral, the first 3D measurements of moisture content in heated concrete, which is believed to be one of the processes directly related to spalling, have been performed using in-situ neutron tomography. In order to follow the fast dehydration process of concrete, one 3D scan (containing 500 radiographs) per minute was captured thanks to the world leading flux at the Institute Laue Langevin (ILL) in Grenoble France. This acquisition speed, which is ten times faster than any other experiment reported in the literature, was sufficient to follow the dehydration process. A dedicated setup, adapted to neutron imaging and high temperature, has been developed for performing such kind of experiments. Concrete samples with different aggregate size have been tested. Quantitative analysis showing the effect of the aggregate size on the moisture distribution is presented. Results on the moisture accumulation behind the drying front, known as the moisture-clog, are also presented and discussed.In parallel, a numerically-efficient coupled thermo-hydro-mechanical (THM) model has been implemented in the finite element software Cast3M for understanding and predicting the complex behavior of concrete at high temperature in the context of spalling. The newly implemented code is remarkably faster (20-30 times) than an existing one, on which it is based. A mesoscopic approach has been adapted to the model for taking into account the heterogeneity of concrete. First the model is applied to experiments from literature monitoring standard parameters such as temperature, gas pressure and mass loss. Then, 1D moisture profiles obtained from neutron radiography experiments are used for verifying and improving the model in terms of some critical constitutive laws such as dehydration and water retention curves. Finally, the model is employed for predicting the 3D moisture distribution measured in this doctoral work via neutron tomography. Among others, mesoscopic THM simulations are performed for investigating the influence of an aggregate on the drying front
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Ichikawa, Yoshikazu. "Prediction of pore pressures, heat and moisture transfer leading to spalling of concrete during fire." Thesis, Imperial College London, 2000. http://hdl.handle.net/10044/1/8721.
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Zaina, Mazen Said Civil & Environmental Engineering Faculty of Engineering UNSW. "Strength and ductility of fibre reinforced high strength concrete columns." Awarded by:University of New South Wales. School of Civil and Environmental Engineering, 2005. http://handle.unsw.edu.au/1959.4/22054.
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The main structural objectives in column design are strength and ductility. For higher strength concretes these design objectives are offset by generally poor concrete ductility and early spalling of the concrete cover. When fibres are added to the concrete the post peak characteristics are enhanced, both in tension and in compression. Most of the available experimental data, on fibre reinforced concrete and fibre reinforced high strength concrete columns, suggest that an improvement in both ductility and load carrying capacity due to the inclusion of the fibres. In this thesis the ductility and strength of fibre reinforced high strength concrete are investigated to evaluate the effect of the different parameters on the performance of columns. The investigation includes both experimental and the numerical approaches with 56 high strength fibre reinforced concrete columns being tested. The concrete strength ranged between 80 and 100 MPa and the columns were reinforced with 1, 2 or 2.6 percent, by weight, of end hooked steel fibres. The effect of corrugated Polypropylene fibres on the column performance was also examined. No early spalling of the cover was observed in any of the steel fibre reinforced column tested in this study. A numerical model was developed for analysis of fibre and non-fibre reinforced eccentrically loaded columns. The column is modelled as finite layers of reinforced concrete. Two types of layers are used, one to represent the hinged zone and the second the unloading portion of the column. As the concrete in the hinged layers goes beyond the peak for the stress verus strain in the concrete the section will continue to deform leading to a localised region within a column. The numerical model is compared with the test data and generally shows good correlation. Using the developed model, the parameters that affect ductility in fibre-reinforced high strength concrete columns are investigated and evaluated. A design model relating column ductility with confining pressure is proposed that includes the effects of the longitudinal reinforcement ratio, the loading eccentricity and the fibre properties and content and design recommendations are given.
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Jerabek, Jakub, Allessandra Keil, Jens Schoene, Rostislav Chudoba, Josef Hegger, and Michael Raupach. "Experimental and Numerical Analysis of Spalling Effect in TRC Specimens." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2009. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1244046893347-05461.
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The paper presents the study of spalling effect occurring under tensile loading in thin-walled TRC specimens. The experimentally observed failure patterns are first classified and the performed experiment design is explained and discussed. A parameter study of spalling effect with varied thickness of concrete cover and reinforcement configurations including both the textile fabrics and the yarns provided the basis for numerical analysis of the effect. The applied numerical model was designed in order to capture the initiation and propagation of longitudinal cracks leading to the separation of concrete blocks from the textile fabrics. A meso-scopic material resolution in a single crack bridge is used for the simulation exploiting the periodic structure of the crack bridges both in the lateral and in the longitudinal direction of the TRC specimens. The matrix was modeled using an anisotropic damage model falling in the microplane-category of material models. The bond between yarn and matrix follows a non-linear bond-law calibrated using pull-out tests. The epoxy-impregnated reinforcement is considered as a homogeneous bar.
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Nince, Andréia Azeredo. "Lascamento do concreto exposto a altas temperaturas." Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/3/3146/tde-27072007-143816/.
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Esta pesquisa foi motivada pela existência de controvérsia na literatura sobre concreto exposto a altas temperaturas, das dúvidas ainda por solucionar acerca da matéria e da lacuna na norma brasileira para a matéria. Este tema reapareceu após os vários acidentes em túneis ao redor do mundo ocorridos nos últimos dez anos, nos quais se verificou a ocorrência de lascamento explosivo de forma intensa, afetando a estabilidade estrutural. O objetivo principal da tese é correlacionar os parâmetros tecnológicos de dosagem (relação água/cimento, teor de argamassa e consumo total de água) às condições de risco de lascamento, associados à umidade ambiente, que indiretamente, influencia no grau de saturação do concreto. O segundo objetivo é otimizar o uso de fibras de polipropileno para minimizar o efeito do lascamento. Adotou-se empregar a curva-padrão H durante 55 minutos em corpos-de-prova cúbicos aquecidos apenas em uma das fases com sua dilatação térmica lateral restringida. O nível de lascamento foi avaliado usando o volume lascado, obtido pela espessura medida diretamente nos corpos-de-prova, multiplicada pela área lascada, calculada pelo AUTOCAD 2000. Os resultados mostraram que o parâmetro tecnológico mais relevante na ocorrência de lascamento foi a relação água/cimento e a umidade ambiente apresentou capacidade de alterar as condições de risco de lascamento. No estudo com as fibras percebeu-se diferentes teores de fibras e diferentes características das fibras para cada grupo de a/c. Conclui-se que a relação água/cimento mais baixa associada a umidade a ambiente mais elevada é a condição mais propícia a ocorrência de lascamento. Conclui-se também que o teor de fibras de 600g/m³ é o teor mínimo para se reduzir o lascamento no grupo a/c=0,50 e 1750g/m³ no grupo a/c=0,25. A fibra L=12mm F=36µm PF=140°C mostrou-se a mais eficaz no grupo a/c=0,50 apenas o comprimento L=6 mm mostrou-se eficiente na redução do lascamento.The present research was motivated by the going controversy in the literature about concrete exposed to high temperatures, the yet unanswered doubts existent on this subject and in the absence of regulation on the matter in Brazil. The theme gained significance after the occurrence of several accidents in tunnels all over the world in the last ten years, in which were observed a very intense form of explosive spalling that affected structural stability of the sites. The main purpose of this work is set up a correlation between technological parameters of dosage in concrete (water cement rate -w/c, mortar content - a, and total water consumption - H) and risk conditions of spalling, which are related to environment humidity that indirectly effects concrete saturation level. The second goal is to optimize the use of polypropylene fiber in order to minimize spalling. The standard H curve was applied during 55 minutes in cubic samples with only a single surface exposed to heat and with restrained lateral thermo dilatation. The response variable was the observed volume of spalling (with multiplied by area of spalling in the sample). The results showed the rate water/cement as the most relevant technology parameter related to spalling risk conditions. Whereas the use of fiber is concerned, efficiency required different fiber content and characteristic for each water/cement rate combined with higher environment humidity provides proper conditions for the occurrence of spalling were 600g/m³ and 1750g/m³ for water/cement ratios of 0,5 and 0,25 respectively. It was also found that the fiber with L=12mm, F=36µm PF=140°C was the most effective in reducing spalling for a water/cement ratio of 0,50 whilst for a effective in reducing spalling for a water/cement ratio of 0,50 whilst for a water/cement ratio of 0,50 whilst for a water/cement ratio 0,25 only the length (L=6 mm) appeared as a significant factor.
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Kirchhof, Larissa Degliuomini. "Estudo teórico-experimental da influência do teor de umidade no fenômeno de spalling explosivo em concretos expostos a elevadas temperaturas." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2010. http://hdl.handle.net/10183/32002.
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Os concretos de alta compacidade, com resistências elevadas (acima de 40 MPa), estão começando a ser cada vez mais usados em obras de infraestrutura e em edificações de grande porte, devido às importantes vantagens que os mesmos oferecem em termos de capacidade de carga e durabilidade. Um dos pontos acerca de seu desempenho que levanta dúvidas envolve o seu comportamento frente a elevadas temperaturas. Evidências coletadas em incêndios ocorridos em estruturas reais, como o do Channel Tunnel e do Mont Blanc Tunnel, indicaram que, sob certas circunstâncias, existe a possibilidade de ocorrência de um fenômeno, conhecido como spalling explosivo, que causa sérios danos por lascamento ao material, incrementando de forma significativa a degradação térmica. Isso ocorre porque a reduzida porosidade e a baixa permeabilidade favorecem o aprisionamento do vapor de água nos poros, gerando um acréscimo da pressão interna que ocasiona tensões que podem superar a resistência à tração do concreto. O processo de spalling, bem como a sua probabilidade e severidade de ocorrência, dependem de uma série de fatores interdependentes que influenciam o comportamento do material. Contudo, está se formando um consenso de que o teor de umidade é o parâmetro mais influente para o desencadeamento do processo. Estudos efetuados após o reconhecimento da existência do spalling explosivo demonstraram que o mesmo tende a ocorrer somente quando o concreto apresenta teores muito elevados de umidade em sua estrutura de poros. Isso restringe a preocupação a certos tipos de elementos onde o concreto pode estar muito úmido por ocasião do sinistro. Embora estes sejam casos raros, a gravidade dos danos devido ao spalling explosivo justifica que se investiguem as condições nas quais o mesmo pode acontecer e se implementem medidas mitigatórias. Dado o caráter recente das investigações sobre o tema, ainda existe uma carência de estudos específicos que apontem quais as combinações críticas de porosidade e teores de umidade que desencadeiam o fenômeno. Este trabalho foi concebido para ajudar a superar essa lacuna de conhecimento, coletando dados sobre as condições que favorecem o spalling explosivo, bem como averiguando quais são as propriedades mecânicas residuais e as alterações na microestrutura sofridas por concretos com vários patamares de resistência submetidos a altas temperaturas. O trabalho utiliza os dados coletados para fundamentar a proposição de um modelo simplificado de spalling, elaborado com o objetivo de prover uma forma de considerar os efeitos do fenômeno durante uma análise termomecânica. Essa é uma necessidade fundamental para complementar os softwares atualmente utilizados para analisar os efeitos de incêndios sobre estruturas. O módulo de spalling foi implementado computacionalmente de forma que pudesse ser utilizado em consórcio com a ferramenta computacional VULCAN, o que permitiu simular a ocorrência do fenômeno na deterioração de uma viga durante um incêndio. Os resultados indicaram que a perda de seção transversal causada pela ocorrência do spalling explosivo reduz substancialmente o tempo de resistência ao fogo (TRRF), devido à aceleração dos danos e à redução da capacidade portante dos elementos estruturais de concreto. Conclui-se, portanto, que é fundamental considerar a possibilidade de lascamentos explosivos em estruturas suscetíveis ao fenômeno. De acordo com o presente estudo, estas incluem aquelas fabricadas com concretos de resistência maior que 40 MPa, que apresentem grau de saturação em torno ou superiores a 90%.In the last years, the utilization of high-strength concrete (HSC) in the construction industry, with compressive strength grades greater than 40 MPa, has become wide spread due to remarkable characteristics of durability and load bearing capacity. However, the increased use of HSC has raised concerns regarding the behaviour of such concretes in fire. Evidences which were collected from structures exposed to the effects of fires, like Channel Tunnel and Mont Blanc Tunnel, have indicated that there is a possibility of the occurrence of explosive spalling in this condition. The phenomenon causes serious damages to the material and raises its thermal degradation in a significant way. This occurs because of its low porosity and permeability that contribute for the vapour pressure build-up in the pores, generating stresses which can exceed tensile strength of the material. The probability and severity of spalling process depend on a large number of inter-dependent factors that influence the behaviour of HSC in an unexpected manner. There is a consensus that the moisture content is one of the principal factors of the occurrence of explosive spalling. Recent investigations have demonstrated that spalling tends to occur only when the moisture content in the pores of concrete is elevated. Although fire is considered an exceptional event, the seriousness of spalling in concrete structures justifies the investigation of conditions in that the phenomenon can be happen and the implementation of preventive measures. In spite of the recent advances about the spalling process in HSC at high temperatures, there is still a lack of information in relation to the critical combinations of factors which affect the spalling occurrence. This work intends to help overcoming this lack of knowledge from the experimental data analysis with the purpose of establishing some critical conditions which collaborate in the spalling process as well as investigating the residual mechanical properties and changes in the microstructure of different concrete grades submitted to high temperatures. In addition, the experimental data are used to validate the proposition of a simplified model of spalling which was developed with the objective to take into account the effects of spalling in the thermo-mechanical analysis. This is an important need to complement the fire analysis of concrete structures. The spalling model was incorporated in the VULCAN software to simulate the phenomenon occurrence in a concrete beam exposed to fire. The results shown that the loss of mass in the beam cross-section, caused by spalling, reduces substantially its required time of fire resistance whereas it accelerates the damage in the concrete and aids the reduction of load bearing capacity of structural element. In conclusion, it is essential to consider the possibility of concrete spalling mainly in concrete grades greater than 40 MPa that present a saturation degree higher than 90%.
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Bosnjak, Josipa [Verfasser], and Joško [Akademischer Betreuer] Ožbolt. "Explosive spalling and permeability of high performance concrete under fire : numerical and experimental investigations / Josipa Bosnjak. Betreuer: Josko Ozbolt." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2014. http://d-nb.info/1058362151/34.
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Bošnjak, Josipa [Verfasser], and Joško [Akademischer Betreuer] Ožbolt. "Explosive spalling and permeability of high performance concrete under fire : numerical and experimental investigations / Josipa Bosnjak. Betreuer: Josko Ozbolt." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:93-opus-95122.
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Mohammadi, Hosinieh Milad. "Behaviour of High Performance Fibre Reinforced Concrete Columns under Axial Loading." Thèse, Université d'Ottawa / University of Ottawa, 2014. http://hdl.handle.net/10393/30726.
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When compared to traditional concrete, steel fibre reinforced concrete (SFRC) shows several enhancements in performance, including improved tensile resistance, toughness and ductility. One potential application for SFRC is in columns where the provision of steel fibres can improve performance under axial and lateral loads. The use of SFRC can also allow for partial replacement of transverse reinforcement required by modern seismic codes. To improve workability, self-consolidating concrete (SCC) can be combined with steel fibres, leading to highly workable SFRC suitable for structural applications. Recent advances in material science have also led to the development of ultra-high performance fibre reinforced concretes (UHPFRC), a material which exhibits very high compressive strength, enhanced post-cracking resistance and high damage tolerance. In heavily loaded ground-story columns, the use of UHPFRC can allow for reduced column sections.
This thesis presents the results from a comprehensive research program conducted to study the axial behaviour of columns constructed with highly workable SFRC and UHPFRC. As part of the experimental program, twenty-three full-scale columns were tested under pure axial compressive loading. In the case of the SFRC columns, columns having rectangular section and constructed with SCC and steel fibres were tested, with variables including fibre content and spacing of transverse reinforcement. The results confirm that use of fibres results in improved column behaviour due to enhancements in core confinement and cover behaviour. Furthermore, the results demonstrate that the provision of steel fibres in columns can allow for partial replacement of transverse reinforcement required by modern codes. The analytical investigation indicates that confinement models proposed by other researchers for traditional RC and SFRC can predict the response of columns constructed with SCC and highly workable SFRC. In the case of the UHPFRC columns, variables included configuration and spacing of transverse reinforcement. The results demonstrate that the use of appropriate detailing in UHPFRC columns can result in suitable ductility. Furthermore, the results demonstrate the improved damage tolerance of UHPFRC when compared to traditional high-strength concrete. The analytical investigation demonstrates the need for development of confinement models specific for UHPFRC.
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Mullins, Sarah K. "The Evaluation on the Effectiveness of Hydrodemolition and Polyaspartic Sealing for Bridge Parapet Wall Protection." University of Cincinnati / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1543920461272325.
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Barbiero, Marialuisa. "Cover cracking of concrete slabs induced by rebar corrosion." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019.
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The phenomenon of concrete cracking due to corrosion of embedded reinforcement steel bars in concrete has been investigated for years. As a consequence of the steel corrosion that is accelerated by cold climates, sea water, spray and from chloride-based acceleration agents, internal cracks form. These agents originate a slow propagation of corrosion products around the embedded steel, forming a passive film, which can be elementary understood as a radial force present all around the steel, creating compressive stresses in concrete. This pressure causes the formation of microcracks that permit the passive film to infill in the structure and propagate. A finite element analysis will be carried out, in order to study the relationship of reinforced concrete features. These are the bar diameter, space between the rebars, concrete strength and the cover thickness. In order to simulate and describe the behaviour of the concrete, the Concrete Damaged Plasticity – CDP, is used. The elastic is easily described by the elastic modulus and the Poisson’s ratio, while the non-linear is more complex. The CDP method considers both compression and tension strengths, gaining as output the cracking pattern. The simulation proposed consists by the modelling of a two-dimensional model, in which the reinforced steel bars will be inserted as holes in the geometric features. The model features internal boundary conditions placed on each side of the rebars/holes. At the end, four groups of simulations are proposed, in which various combinations of the parameters considered, are provided. These corresponds of four different concrete strengths, three different diameters of the steel rebars, five different cover thicknesses and four different spacings between the rebars. The simulations show the probable cracking paths, based on the internal displacement given by the pressure formed by the corrosion products.
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Hothan, Sascha, and Daniel Ehlig. "Hochtemperaturverhalten von Stahlbetonplatten mit Textilbetonverstärkung." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-78024.
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Die Verwendung von Endlosfilamenten aus Carbon als Bewehrungsmaterial für Beton, sogenannter Textilbeton, bietet die Möglichkeit der Sanierung und der Verstärkung bestehender Stahlbetonkonstruktionen. Dabei muss die Frage nach dem Feuerwiderstand von derart verstärkten Tragwerken beantwortet werden. Aufschluss darüber liefern Brandversuche. Mit Textilbeton verstärkte Stahlbetonplatten haben in Brandversuchen nach der Einheits- Temperaturzeitkurve bei 33 % der Traglast mehr als 60 Minuten standgehalten. Bei 50 % der Traglast kam es nach einer Branddauer von 55 Minuten, bei 65 % nach 30 Minuten, zu einem Zugversagen der textilen Verstärkungsschicht. Bei während des Brandes unbelasteten bzw. gering belasteten Platten lagen die im Anschluss ermittelten Resttragfähigkeiten bei 65 % der Bruchlast nach 30 Minuten Branddauer bzw. bei 50 % der Bruchlast nach 60 Minuten Branddauer. Während und nach der Beflammung waren zunehmende Durchbiegungen und Rissbreiten erkennbar. Es traten aber keine Abplatzungen auf, weshalb die Verstärkungsschicht aus Textilbeton als zusätzliche Betondeckung für die Stahlbewehrung angerechnet werden kann. Diese außerordentlich positiven Ergebnisse zeigen, dass für verstärkte Konstruktionen Feuerwiderstandsklassen von F60 bzw. R60 ohne zusätzliche Maßnahmen erreicht werden können. Dies ist von hoher Relevanz für die wirtschaftliche Anwendung dieser Verstärkungsmethode. Für ein umfassendes Verständnis der Interaktion zwischen den Bewehrungen Textil und Stahl sowie der Versagensmechanismen während des Brandes, sind weitere Erkenntnisse über die mechanischen Eigenschaften von Textilbeton im Hochtemperaturbereich nötig. Auch der Einfluss der Oxidation des Carbons konnte nicht abschließend beurteilt werdenUsing endless carbon filaments for concrete reinforcement, so called textile reinforced concrete, the possibility of reconstruction and strengthening of existing concrete structures arises. The question concerning fire resistance of structures strengthened like this has to be answered. Fire tests provide answers. Steel reinforced concrete slabs strengthened with textile reinforced concrete loaded with 33 % of ultimate load survived an ISO-fire for 60 minutes. Loaded with 50 % and 65 % of ultimate load the slabs failed after 55 minutes and 30 minutes of fire exposure due to tension failure of the textile reinforcement layer. Slabs not loaded or with a low load level during fire exposure showed remaining bearing resistances of 65 % of ultimate load after 30 minutes and 50 % of ultimate load after 60 minutes of fire exposure. During and after fire exposure rising deflections and growing crack widths were observed. However no spalling occurred. Therefore the textile reinforced concrete layer can be taken into account as concrete covering for the steel reinforcement. Those extraordinary positive results document, that reinforced concrete structures with additional fibre reinforced concrete can achieve fire resistance classes of R60 without additional provisions. To achieve comprehensive understanding of interaction between steel and fibre reinforcement and failure mechanisms in case of fire more knowledge concerning the mechanic properties of fibre reinforced concrete at high temperatures is essential. The influence of oxidation of the carbon fibres could not fully be answered
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Lukic, Bratislav. "Mise au point d'une technique de mesure de champs pour la caractérisation du comportement dynamique du béton en traction." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAI028/document.
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Ce travail thèse a pour objet une méthode expérimentale combinant un essai de traction indirect par écaillage et une mesure de champs à partir d’images obtenues par caméra ultra rapide, ceci à des fins d’identification des propriétés de rupture du béton sous chargement de traction dynamique. Cette méthode, proposée dans la littérature peu de temps avant le démarrage de ces travaux, fait ici l’objet d’une étude approfondi ainsi que d’une série de développements et d’amélioration. Les images obtenues sont traités par une technique de grille et la méthode des champs virtuels est appliquée pour identifier le comportement local des matériaux quasi-fragiles soumis à de hautes vitesses de déformation (plusieurs 100 1/s}). Dans un premier temps, afin de valider la technique de traitement maus aussi d’étudier l’incertitude de mesure associée, un simulateur de la chaîne de mesure complète a été mis au point. Il a été ainsi possible d’étudier l’influence de différentes sources potentielles d’erreurs qui peuvent être rencontrées dans le protocole expérimental. Cette étude a permis de retenir des recommandations sur les conditions de réalisations réelles de l’essai afin d’améliorer la fiabilité des mesures obtenues. D’un point de vue expérimental, différents capteurs ultra haute vitesse ont été utilisés afin d’étudier leur performances vis-à-vis des mesures réalisées. Ainsi, les campagnes d’essais ont été réalisées sur un matériau aux caractéristiques bien identifiées permettant l’étude des performances métrologiques de toute la chaine d’identification, pour chaque modèle de capteur. Enfin, le protocole expérimentale a été mis en place pour étudier le comportement de plusieurs types de béton soumis en traction dynamique. L’objectif, ici, est d’identifier leur comportements mécaniques ainsi que leur caractéristiques de rupture et fragmentation sous traction dynamique. En ce qui concerne la résistance à la traction, les valeurs identifiées dans cette étude sont inférieures, pour chaque cas, à celles rapportées dans la littérature et obtenues, pour la plupart, à partir du traitement de la vitesse matérielle mesurée en face arrière de l’échantillon. Pour ce qui est de l’énergie spécifique de rupture, les valeurs obtenues dans ces travaux sont égalements inférieures à celles publiées dans les revues scientifiquesIn this thesis a recently proposed photomechanical spalling experiment has been used in light of identifying concrete failure properties under dynamic tension.The experimental technique uses ultra-high speed imaging, the grid method and the virtual fields method.First, in order to investigate the accuracy and validate the processing technique, a methodology of using simulated experiments has been developed by numerically simulating the entire identification process.In this way, several potential sources of errors have been investigated allowing to place guidelines on how to perform the experiment in a more reliable manner.Second, several latest ultra-high speed acquisition systems have been used in order to investigate their contribution to a possible measurement refinement.In this case, the trial experiments have been conducted on a material of known characteristics which allowed investigating the metrological performance of the acquisition system on the entire identification chain.Finally, the experimental methodology has been applied to testing several grades of concrete in light of identifying the material constitutive response as well as their fracturing characteristics under dynamic tension.The identified tensile strengths in this work were found to be consistently lower than those obtained from the standard processing of the rear-face velocity profile.Moreover, the values of the identified specific fracture energy were also found to be markedly lower than the ones often reported in the literature
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Maluk, Cristian. "Development and application of a novel test method for studying the fire behaviour of CFRP prestressed concrete structural elements." Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/15926.
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A novel type of precast, prestressed concrete structural element is being implemented in load-bearing systems in buildings. These structural elements combine the use of high-performance, self-consolidating concrete (HPSCC) and non-corroding carbon fibre reinforced polymer (CFRP) prestressing tendons; this produces highly optimized, slender structural elements with excellent serviceability and (presumed) extended service lives. More widely, the use of new construction techniques, innovative materials, and ground-breaking designs is increasingly commonplace in today's rapidly evolving building construction industry. However, the performance of these and other structural elements in fire is in general not well known and must be understood before these can be used with confidence in load-bearing applications where structural fire resistance is a concern. Structural fire testing has traditionally relied on the use of the standard fire resistance test (i.e. furnace test) for assuring regulatory compliance of structural elements and assemblies, and in many cases also for developing the scientific understanding of structural response to fire. Conceived in the early 1900s and fundamentally unchanged since then, the standard testing procedure is characterized by its high cost and low repeatability. A novel test method, the Heat-Transfer Rate Inducing System (H-TRIS), resulting from a mental shift associated with controlling the thermal exposure not by temperature (e.g. temperature measured by thermocouples) but rather by the time-history of incident heat flux, was conceived, developed, and validated within the scope of the work presented in this thesis. H-TRIS allows for experimental studies to be carried out with high repeatability, imposing rationally quantifiable thermal exposure, all at low economic and temporal cost. The research presented in this thesis fundamentally seeks to examine and understand the behaviour of CFRP prestressed HPSCC structural elements in fire, with emphasis placed on undesired 'premature' failure mechanisms linked to the occurrence of heat-induced concrete spalling and/or loss of bond between the pretensioned CFRP tendons and the concrete. Results from fire resistance tests presented herein show that, although compliant with testing standards, temperature distributions inside furnaces (5 to 10% deviation) appear to influence the occurrence of heat-induced concrete spalling for specimens tested simultaneously during a single test; fair comparison of test results is therefore questionable if thermal exposure variability is not explicitly considered. In line with the aims of the research presented in this thesis, H-TRIS is used to carry out multiple comprehensive studies on the occurrence of concrete spalling and bond behaviour of CFRP tendons; imposing a quantified, reproducible and rational thermal exposure. Test results led to the conclusion that a "one size fits all" approach for mitigating the risk of heat-induced concrete spalling (e.g. prescribed dose of polypropylene (PP) fibres included in fresh concrete), appears to be ineffective and inappropriate in some of the conditions examined. This work demonstrates that PP fibre cross section and individual fibre length can have an influence on the risk of spalling for the HPSCC mixes tested herein. The testing presented herein has convincingly shown, for the first time using multiple repeated tests under tightly controlled thermal and mechanical conditions, that spalling depends not only on the thermal gradients in concrete during heating but also on the size and restraint conditions of the tested specimen. Furthermore, observations from large scale standard fire resistance tests showed that loss of bond strength of pretensioned CFRP tendons occurred at a 'critical' temperature of the tendons in the heated region, irrespective of the temperature of the tendons at the prestress transfer length, in unheated overhangs. This contradicts conventional wisdom for the structural fire safety design of concrete elements pretensioned with CFRP, in which a minimum unheated overhang is generally prescribed. Overall, the research studies presented in this thesis showed that a rational and practical understanding of the behaviour of CFRP prestressed HPSCC structural elements during real fires is unlikely to be achieved only by performing additional standard fire resistance tests. Hence, H-TRIS presents an opportunity to help promote an industry-wide move away from the contemporary pass/fail and costly furnace testing environment. Recommendations for further research to achieve the above goal are provided.
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Silva, Janaina Salustio da. "Estudo de concretos de diferentes resist?ncias ? compress?o submetidos a altas temperaturas sem e com incorpora??o de fibras de politereftalato de etileno (PET)." Universidade Federal do Rio Grande do Norte, 2013. http://repositorio.ufrn.br:8080/jspui/handle/123456789/14844.
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The reinforced concrete structures are largely used in buildings worldwide. Upon the occurrence of fire in buildings, there is a consensus among researchers that the concrete has a high resistance to fire, due mainly to its low thermal conductivity. However, this does not mean that this material is not affected by exposure to high temperatures. Reduction of the compressive strength, modulus of elasticity, discoloration and cracking, are some of the effects caused by thermal exposure. In the case of concretes with higher resistance occurs even desplacamentos explosives, exposing the reinforcement to fire and contributing to reducing the support capacity of the structural element. Considering the above, this study aims to examine how the compressive strength and porosity of concrete are affected when subjected to high temperatures. Were evaluated concrete of different resistances, and even was the verified if addition fibers of polyethylene terephthalate (PET) in concrete can be used as an alternative to preventing spalling. The results indicated that explosive spalling affect not only high strength concrete whose values of this study ranged from 70 to 88 MPa, as well as conventional concrete of medium strength (52 MPa) and the temperature range to which the concrete begins to suffer significant changes in their resistance is between 400 ? C and 600 ? C, showing to 600 ? C a porosity up to 188% greater than the room temperature
As estruturas de concreto armado s?o largamente utilizadas nas edifica??es em todo o mundo. Quando da ocorr?ncia de inc?ndio em edifica??es, ? consenso entre os estudiosos, que o concreto apresenta uma elevada resist?ncia ao fogo, devido principalmente a sua baixa condutividade t?rmica. No entanto, isto n?o significa que esse material n?o seja afetado pela exposi??o a elevadas temperaturas. Redu??o de resist?ncia ? compress?o e no m?dulo de elasticidade, altera??o na colora??o e aparecimento de fissuras, s?o alguns dos efeitos causados pela exposi??o t?rmica. No caso de concretos com resist?ncia mais elevada, ocorre ainda desplacamentos explosivos, expondo as armaduras ao fogo, e contribuindo assim para a redu??o da capacidade suporte do elemento estrutural. Diante do exposto, o presente trabalho tem por objetivo analisar como a resist?ncia ? compress?o e a porosidade do concreto s?o afetadas quando submetido a elevadas temperaturas. Foram avaliados concretos de diferentes resist?ncias, e ainda foi verificado se a incorpora??o de fibras de politereftalato de etileno (PET), em matriz de concreto, pode ser usada como alternativa a preven??o do lascamento. Os resultados indicaram que lascamentos explosivos acometem n?o somente os concretos de alta resist?ncia, cujos valores desta pesquisa variaram de 70 a 88 MPa, como tamb?m o concreto convencional de m?dia resist?ncia (52 MPa), e que a faixa de temperatura para o qual o concreto come?a a sofrer altera??es expressivas em sua resist?ncia fica entre 400 ?C e 600 ?C, apresentando aos 600 ?C uma porosidade at? 188% maior que a apresentada a temperatura ambiente
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Malmros, Catrine, and Johnson Andrea. "Brandpåverkan på skyddskonstruktioner i funktionsskyddsrum : En undersökning av resthållfasthet i betongbalkar." Thesis, Mälardalens högskola, Akademin för ekonomi, samhälle och teknik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:mdh:diva-40032.
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In the beginning of the 21st century decisions were made regarding the decommission of the total defence in Sweden. Since then the security policy situation has changed, regarding both the risk of war and other types of treats such as terrorism. Due to this the total defence is now being re-established. The Swedish Fortifications Agency and Research Institutes of Sweden (RISE) has initiated the Centre of excellence for fortification (CFORT) to support the development of competence in fortification. In case of a crisis or war secured function shelters constitutes a significant part of the Swedish total defence by protecting important technology and activity.The purpose of this bachelor thesis is to investigate the remaining load bearing capacity in concrete constructions in secured function shelters after exposure to fire. This will provide a foundation for further research within the area of the effects of fire in secured function shelters. To achive this, experiments were conducted on nine concrete beams which were casted according to calculations based on the structural codes of the Swedish Fortifications Agency (FKR). Since fully scaled beams are difficult to manage and would not fit in the equipment being used, the beams were casted in a smaller size; 2000 x 150 x 210 mm. Samples of the concrete and the reinforcement were sent to the Swedish Cement and Concrete Research Institute (CBI) for tests which provided actual values of the compressive strength, yield point and modulus of elasticity. Six of the beams were in pairs exposed to fire in a specially built oven according to three different temperature curves. All the beams were later subjected to load until failure. Calculations regarding load bearing capacity were executed with both theoretical and actual values obtained from CBI. The results were compared to the results from the loading tests. During the last fire experiment the beams spalled, most likely due to the quickly rising temperature. The loading test showed that the strength of the beams which had not spalled were not significantly lower than the unaffected beams. Those beams showed a reduction of only 0 – 6 %. However, the beams which had spalled showed a reduce in strength of approximately 20 %.Centrum för fortifikatorisk kompentens
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Ehlig, Daniel, Frank Jesse, and Manfred Curbach. "Stahlbetonplatten verstärkt mit Textilbeton unter Brandbelastung." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2009. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1244050720109-69672.
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Im Rahmen experimenteller Untersuchungen wurden Stahlbetonplatten hergestellt, mit verschiedenen textilen Bewehrungen verstärkt, mit 125 % Gebrauchslast vorgeschädigt und anschließend unter Gebrauchslast mit einer Brandbelastung nach der Einheitstemperaturkurve (ISO-834, Cellulosic curve) beaufschlagt. Alle Platten hielten der Brandbelastung bei gleichzeitiger Biegebeanspruchung mehr als 60 Minuten stand und zeigten weder Betonabplatzungen noch andere optische Schädigungen auf. Die für dieses überraschend positive Ergebnis verantwortlichen Mechanismen werden diskutiert, sind aber noch nicht vollständig verstanden. Eine Schlüsselrolle spielt dabei vermutlich das gute Rissverhalten von Textilbeton und interne Umlagerungen zwischen Textil und Stahlbewehrung.
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Dvořáková, Michaela. "Studium chování betonu při působení vysokých teplot." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2014. http://www.nusl.cz/ntk/nusl-226711.
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The aim of this diploma thesis is to focus on the resistance of concrete exposed to high temperatures especially with focus of resistance against explosive spalling as well as clarifying the mode of action of various types of polypropylene fibres. The theoretical part is an introduction to the issues of explosive spalling, its mechanisms and majority influencing factors. Further description of the processes taking place in the structure of concrete under extreme thermal load, distribution and size of pores in concrete, thermal load, temperature-time curves and their applications, methods of elimination of negative behaviour of concrete exposed to thermal loading (passive and active methods), mode of action of polypropylene fibres and more is also included in the theoretical part. The main aim of experimental part is to verify the function of polypropylene fibers of various Melt Flow Indexes (MFI) and dosage. Primarily, the test samples with content of the PP-fibers are compared to the reference sample without fibers. Secondarily, the samples with standard PP-fibers (with MFI 25) with dosage 2.0 kg/m3 are compared to samples with modified PP-fiber (with MFI 2500) of dosage 0.9 kg/m3. Photogrammetric images were used for evaluation and comparison of spalled surfaces and its depth. Determination of the softening temperature and melting point of the modified and standard PP-fibers was made by using a high temperature microscope video. The second part of the experimental work was to define concrete permeability at different temperatures and pressures. Permeability was measured at temperatures of 20°C, 90°C, 150°C, 175°C, 200°C, 225°C and 250°C and at pressure of 0.2, 0.4 and 0.6 MPa.
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Phan, Minh Tuyen. "Modélisation explicite de l’écaillage sous incendie du béton : approche thermo-hydro-mécanique avec des conditions aux limites évolutives." Thesis, Paris Est, 2012. http://www.theses.fr/2012PEST1155/document.
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Dans les dernières années, les incendies majeurs dans les tunnels ont causé des dommages importants. Dans ces conditions extrêmes (la température dépasse rapidement 1200 °C), l'augmentation de pression dans les pores, la dilatation thermique empêchée, l'incompatibilité de dilatation thermique entre la pâte du ciment et des granulats, la déshydratation ... sont des principaux mécanismes de dégradation qui peuvent être à l'origine de l'écaillage. L'écaillage progressif pendant l'incendie se manifeste par le détachement de la surface du béton par petits morceaux réduisant ainsi la section résistante et pouvant conduire à une rupture prématurée de la structure. Dans cette thèse, un modèle éléments finis THM est enrichi par un modèle d'écaillage progressif en proposant un critère d'écaillage de type détachement-flambement. La partie thermo-hydrique du modèle THM est basée sur l'approche à trois fluides en milieux partiellement saturés. Le comportement mécanique est développé dans le cadre d'une approche thermo-poro-mécanique couplée à l'endommagement et à la plasticité adoucissante. Cette modélisation de l'écaillage conduit à un problème avec frontière et conditions aux limites évolutives. Une stratégie de résolution numérique sans remaillage a été développée pour transférer les conditions aux limites THM simultanément avec l'occurrence de l'écaillage. L'implémentation du modèle dans le code aux éléments finis CESAR-LCPC a permis de procéder à différentes études paramétriques et à des confrontations avec des essais pour évaluer les capacités opérationnelles du modèle à décrire l'occurrence de l'écaillage et identifier les paramètres majeurs qui la contrôlentIn the recent years, there were major tunnels fires which caused fatalities and severe traffic restrictions. In such extreme conditions (temperatures exceeding 1200 °C for considerable time spans), pore pressure build-up, restrained thermal dilatation, cement paste to aggregate incompatibility, dehydration... are some main degradation mechanisms of concrete that may cause its thermal spalling. Progressive concrete spalling occurring during a fire presents as the breakdown of surface layers which flake into small pebble-like pieces. Then, the resistant section of the structure reduces which may lead to its premature failure.In this thesis, a THM finite element model is enriched with a detachment-buckling type criterion for progressive spalling. The thermo-hygral part of the THM model is based on the three fluid approach for partially saturated porous media. The mechanical part is derived within the framework of thermo-poro-mechanics coupled to damage and softening plasticity.The adopted modeling of spalling leads to a problem with evolving boundary and boundary conditions. A suitable numerical solution strategy without remeshing is then developed in order to transfer properly the THM boundary conditions simultaneously with spalling occurrence.The efficiency of the model THM-Spalling is illustrated by some numerical examples and by parametric studies. These studies identify the influence, on spalling, of size variation of spalling flakes, the average spalling velocity and uncertainties on different material parameters. Confrontation with experimental tests shows satisfactory capacity of the THM-Spalling model in reproducing qualitatively the occurrence of spalling
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Šottl, Jiří. "Vývoj správkové malty s odolností proti vysokým teplotám." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2014. http://www.nusl.cz/ntk/nusl-226731.
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Currently, increasing reinforced concrete structures and concrete structures that require repair in the form of remediation. The master’s thesis deals with the development of repair mortars with resistance to high temperatures, which would allow the re-profiling of the fire damaged parts of the structures and restore its function. Development of repair mortars is based on a literature review of articles dealing with research materials resistant to high temperatures.
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Sultangaliyeva, Fariza. "Formulation of fluid fire-resistant fiber-reinforced cementitious composite : Application to radioactive waste disposal." Thesis, Pau, 2020. http://www.theses.fr/2020PAUU3041.
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Le but de ce travail est de développer un béton fluide résistant au feu renforcé en fibres de polypropylène pour les colis de stockage des déchets radioactifs de moyenne activité à vie longue. Le défi de ce travail consiste à utilizer des fibres de polypropylène qui, même ajoutées en petite quantité, améliorent la résistance au feu mais diminuent de manière significative la maniabilité des bétons frais. Des essais à l’échelle du laboratoire sont effectués afin d’évaluer les comportements rhéologique et à haute température des matériaux cimentaires contenant des fibres de polypropylène. Dans la première partie, une étude du comportement rhéologique des matériaux cimentaires avec des fibres de polypropylène a été réalisée. Le but de cette étude est d’étudier l’influence de ces fibres sur le seuil d’écoulement des pâtes de ciment et des mortiers. Un modèle qui permet d’évaluer la quantité de pâte supplémentaire nécessaire pour compenser l’effet des fibres de polypropylène en fonction de la fluidité du béton frais a été développé.Ensuite, une étude expérimentale et numérique sur le comportement des matériaux cimentaires avec des fibres de polypropylène à haute température a été réalisée afin d’optimiser le choix des fibres pour améliorer la stabilité thermique d’un matériau cimentaire. Des essais de perméabilité résiduelle radiale et des essais feu sur les trois matériaux avec squelettes granulaires différents contenant des fibres de polypropylène de différentes géométries et dosages ont été réalisés dans un but de sélectionner une géométrie et un dosage optimal des fibres. Puis, des simulations thermomécaniques ont été développées à l’échelle macroscopique et mésoscopique. Le choix du diamètre, de la longueur et du dosage des fibres a été fait en fonction de la taille maximale des granulats.Finalement, une méthode de formulation du béton autoplaçant avec des fibres de polypropylène optimisé à la fois du point de vue de la rhéologie et de la résistance au feu a été présentée. Avec cette méthode, la conformité aux critères imposés sur les propriétés à l’état frais et à l’état durci du béton est vérifiée. Des éprouvettes de bétons sont testées sous chargement mécanique uniaxial et, en fonction des résultats, les formulations finales sont sélectionnées pour les futurs essais feu à l’échelle plus importanteThe aim of the thesis is to design a self-compacting concrete with polypropylene fibers resistant to fire for a use in storage containers of medium activity long-lived waste. The challenge of the work is presented by the use of polypropylene fibers that enhance fire resistance but drastically diminish workability of concrete even when added at small volume fractions. Tests on laboratory scale are conducted with a purpose of evaluating rheological behavior and high temperature behavior of cementitious materials containing polypropylene fibers.In the first part, a study of rheological behavior of cement-based materials containing polypropylene fibers was done. The aim of this study is to investigate the influence of polypropylene fibers on the yield stress of cement pastes and mortars. A model is proposed to be able to evaluate the quantity of paste necessary to compensate the addition of polypropylene fibres according the fluidity of fresh concrete.Then an experimental and numerical investigation of behavior of cementitious materials with polypropylene fibers at high temperature was done so as to optimize the choice of polypropylene fibers for cementitious material to improve its thermal stability. Three different cementitious materials with three different granular skeleton containing various polypropylene fiber geometries and dosages were tested (residual radial permeability test and fire test) in order to select an optimal fiber geometry and dosage. Then thermomechanical computations was developped at maco and meso scale. Then, a choice of diameter, length and dosage of fibres is proposed according to the maximum size of gravels.Finally, a method of concrete formulation with polypropylene fibers optimized from perspectives of rheology and resistance to fire is presented. In this method, fresh and hardened state properties are verified to ensure an accordance with performance criteria specified by the project. At the end, designed mixes were tested in fire tests conducted on uniaxially compressed prisms and, based on outcomes, final mixes are selected for further fire tests on higher scale concrete
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Sovová, Kateřina. "Studium chování vysokopevnostních betonů při působení vysokých teplot." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2017. http://www.nusl.cz/ntk/nusl-295664.
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This master’s thesis is divided into two parts; practical and theoretical. The theoretical part of this study describes the influence of high temperature on concrete structure and chemical, mechanical and physical changes, which take place during the exposure to high temperatures. The thesis also evaluates spalling of concrete and the methods to prevent it, as well as the function of polypropylene and cellulose fibers in the concrete. The practical part deals with design, production and testing of the cement-based concrete with the use of different fibers (polypropylene fibers and cellulose fibers). The properties and the means of applications in high temperatures are also included. The practical part also assesses the influence of high temperature on strength, porosity, visual changes of specimens, changes of surface and degradation of testing specimens due to heat loads according to normative heat curve (ISO 834) and also according to hydrocarbon curve. For clearer arrangement, the experimental tests are divided into two parts and the measured values are evaluated at the end of each part. The conclusion resumes all data obtained by testing and evaluates what is the most suitable formulation. The approach for further research is also discussed.
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Fiala, Jiří. "Studium chování betonů při působení vysokých teplot." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2015. http://www.nusl.cz/ntk/nusl-227178.
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This thesis deals with the behavior of cement concrete at high temperature with a focus on the impact behavior of aggregate, cement type and polypropylene fiber reinforcement. The theoretical part describes the issue of cement concrete at high temperatures, especially processes in the cement matrix, aggregates and polypropylene fibers. Furthermore, theoretical part describes the selection of a suitable type of cement and aggregates in concrete exposed to high temperatures. In the experimental part was designed the concrete composition with various kinds different types of aggregates and two types of cements. The temperature stress of test samples was performed according to ISO standard temperature curve 834. Subsequently, was made the verification of the physic-mechanical properties such as changes in bulk density and compressive strength after heat load. Moreover, the surface appearance of samples after heat load was evaluated, especially the occurrence of samples, the crack width and explosive spalling. Mineralogical composition changes of prepared samples before and after heat load were observed via X-ray diffraction analysis. Finally, we made a photogrammetry on a test plates after heat load which defined the size of the area and depth of spalling concrete surface.
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Rozsypalová, Iva. "Stavebně technický průzkum objektu poškozeného požárem." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2015. http://www.nusl.cz/ntk/nusl-227489.
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Diploma thesis summarizes knowlegde related to the behavior of structures and material in the fire, focusing mainly on concrete and reinforced concrete structures. It deals with the design and implementation of diagnostic work of Building no. 103 in complex Svit Zlín affected by a large fire. There are presented evaluation of laboratory experiments of samples and static analysis.
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Dunkman, David Andrew. "Bursting and spalling in pretensioned U-beams." Thesis, 2009. http://hdl.handle.net/2152/ETD-UT-2009-12-406.
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An experimental program was conducted at the Ferguson Structural Engineering Laboratory of The University of Texas at Austin, under the auspices of Texas Department of Transportation (TxDOT) Research Project 5831, to investigate the tensile stresses that develop in the end regions of pretensioned concrete U-beams at transfer of prestress. Understanding the effect of these “bursting” and “spalling” stresses is essential in order to design standard details that might lead to reliably-serviceable end regions.
Two full-scale beam specimens, designed to be worst-case scenarios for bursting and spalling, were fabricated. Each beam had one square and one highly skewed end. Extensive instrumentation, including strain gages on transverse and lateral reinforcing bars, was employed in the end regions of these U-beams. Experimentally determined bursting and spalling stresses in these bars were compared to results of past projects (from the literature) investigating I-beams and inverted T-beams.
Preliminary recommendations are made for changes in the standard reinforcing details for U-beam end regions. Such recommended details will be tested in the upcoming phase of Research Project 5831.text
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ZHENG, JI_CHENG, and 鄭吉誠. "Spalling of Flowable Steel Fiber Reinforced Concrete at High Temperature." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/20980487739220480138.
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Luckai, Jeffrey W. "Evaluating the Effects of Spalling on the Capacity of Reinforced Concrete Bridge Girders." Thesis, 2011. http://hdl.handle.net/10012/6229.
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Corrosion of the reinforcing steel is a primary deterioration mechanism for reinforced concrete bridges. Heavy use of de-icing salts is believed to be a major contributor in Ontario to severe girder soffit spalling in certain cases. This thesis develops an assessment methodology to evaluate spalled bridges based on ultimate limit states. Specifically, a deterministic program is developed for assessment. It is subsequently compared to laboratory test results and used as a basis for a probabilistic reliability study.
A modified area concept is proposed in this thesis to consider the effects of exposing reinforcement at various locations along the girder length. A multipoint analysis program, BEST (Bridge Evaluation Strength Tool), is developed that employs this concept, along with graphical spalling surveys and structural drawings, to evaluate reinforced concrete bridge girders. The program is adapted for a full bridge analysis and to consider the other effects of corrosion, such as bar section loss and bond deterioration.
A case study bridge is evaluated to show that the BEST program offers a viable tool for the rapid assessment of spalled bridge girders and to facilitate the prioritization of rehabilitation projects. This evaluation indicates that the spatial distribution of the spalling along a girder, relative to bar splices and laps, has the most significant influence on structural capacity. Single girders show strength deficiencies in flexure and shear due to spalling. In general, the consideration of system effects improves the predicted bridge condition, while considering section loss and bond deterioration has the opposite effect.
Laboratory work is used to validate the proposed model and identify a number of areas for future research. The laboratory test results also suggest that the current repair methods are effective in restoring bond and strength.
In order to further explore potential uses for the BEST program, modifications are made so that it can be used to perform reliability analyses using Monte-Carlo simulation techniques.
A simplified approach for estimating the reliability index as a function of the deterministic resistance ratio is proposed based on the reliability analysis results.
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Wu, Miin Chyi, and 吳敏祺. "Factors affect the spalling behavior of high strength concrete in fire and its material properties after fire." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/41229957923159006925.
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