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Evaluation fiabiliste de l'impact des facteurs climatiques sur la corrosion des poutres en béton armé : application au cas libanais

Abstract : When exposed to aggressive environment, reinforced concrete structures are subject to a degradation mechanism that affects their integrity. Among various environmental attacks, the corrosion of RC structures is considered the most dangerous. The process is launched by the penetration of aggressive agents, precisely the chlorides and carbon dioxide into the concrete. The chlorides induce a localized corrosion, also called pitting corrosion, while on the other hand the carbon dioxide leads to a general corrosion called uniform corrosion. This corrosion phenomenon depends on several factors such as the materials characteristics,loadings, geometry and the environment. All these components include different levels of uncertainties that are taken into account throughout a probabilistic approach. In this work, we propose two models for the corrosion mechanisms induced separately by the chlorides and the carbon dioxide. These models take into account the effect of the climatic condition that is mainly described by the temperature and the relative humidity. In addition to that, as a study case we have treated in details the Lebanese climatic context. We have proposed a physical model of steel corrosion in reinforced concrete beams that occurs in two phases : - An initiation phase where aggressive agents like the chlorides and carbon dioxide penetrate into the concrete and reach a critical concentration values causing the depassivation of the steel ; - A propagation phase in which the active corrosion of steel decreases the strength of the beam leading to its failure. All the factors that have uncertainties are treated as random variables. Several probabilistic models are listed and discussed in the literature while only the models that match with our context are selected. The reliability analysis allowed us to assess the reliability of beams subjected to corrosion in ULS and SLS. The loss of steel section due to the corrosion mechanism induces a decrease of the bearing beam capacity, and an increase in the tension stress in the concrete.This causes an increase of the width of cracks openings. Thus, taking into account the serviceability limit state, the safety margin goes to zero when the width of crack opening exceeds the acceptable width as recommended by the Eurocode 2. The limit state function in ULS is the bending strength. The failure occurs when the applied moment equals or surpasses the resisting moment. The reliability calculations are carried out using Monte-Carlo simulations. Finally, several applications to the corrosion model are proposed via this work. The first application concerns the sensitivity analysis of the corrosion models for the different parameters. The effects of the mean values and the variability of the random variables on the model response are also examined. The impact of climatic factors on the corrosion phenomenon took the biggest part of this work. We have applied the chloride’s corrosion model with the real temperatures and relative humidity of three coastal cities having different climatic characteristics. Then a comparative study showing the effect of the ba rdiameters and the cover thickness on the reliability of the RC beam subjected to aggressive environment is carried out. (...)
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Submitted on : Wednesday, September 21, 2011 - 6:47:20 PM
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Jinane El Hassan. Evaluation fiabiliste de l'impact des facteurs climatiques sur la corrosion des poutres en béton armé : application au cas libanais. Autre. Université Blaise Pascal - Clermont-Ferrand II, 2010. Français. ⟨NNT : 2010CLF22064⟩. ⟨tel-00625536⟩



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