Agradeço primeiramente a Deus, princípio e fim de todas as coisas. A toda a minha família e em especial aos meus pais Gabriella e Lino por sempre me incentivarem nos estudos e por todo o amor incondicional doado. Mãe, pai, para mim vocês são preciosos exemplos de dedicação e altruísmo sincero. A Sonia, amada companheira de caminhada pelas estradas da vida. Longe ou perto, todo o amor, cumplicidade, paciência e apoio a mim dedicados foram fundamentais para eu chegar até aqui. Obrigado. Ao professor e orientador Edson D. Leonel, que com a sua tranquilidade e serenidade forneceu bases sólidas onde pude me apoiar sempre que precisei. Agradeço pela disponibilidade constante, atenção, paciência e confiança depositada em mim. Ao professor André T. Beck pelo incentivo e suporte prestado no aprendizado da teoria de confiabilidade. Em meio a um universo de incertezas, sua expressiva influência na minha formação acadêmica eu considero como certa. Ao professor Caio G. Nogueira, pela grande ajuda na implementação computacional e pelas preciosas sugestões ao longo do desenvolvimento do trabalho. Ao professor Andrés B. Cheung, exemplo de humildade e dedicação, pela amizade, pelas conversas e pelo incentivo, sem os quais provavelmente eu não teria escolhido cursar o mestrado. Obrigado por ter me ajudado a escolher esse caminho que indubitavelmente expandiu meus horizontes.
The reinforcement’s depassivation in reinforced concrete structures occurs when the chloride concentration at the reinforcement’s interface reaches the threshold content. The depassivation phenomenon starts the propagation period, in which huge mechanical degradation processes are triggered. Moreover, it is well established that the propagation period is considerably shorter than the initiation period. Therefore, the accurate prediction of the corrosion time initiation is a major issue in structural durability domain. This study presents a transient formulation based on the Boundary Element Method (BEM) for the corrosion time initiation assessment. The diffusion fields evaluated by the BEM are utilized into a probabilistic framework, which enables the assessment of probabilistic values for corrosion time initiation. Therefore, the formulation handles properly the uncertainties in this problem, which is largely subjected to randomness. Three applications are presented. The robustness and accuracy of the proposed approach over classical analytical models are highlighted.
Every structure is subjected to the effects of time and environment on which they are located. The consideration of these effects and their consequences in design phase is called nowadays as durability analysis of the structural system. The corrosion of the reinforcement steel through the chloride penetration inside the concrete is the main cause of the lifetime deterioration of the reinforced concrete structures. As a direct consequence, the corrosion affects the resistant capacity of the structural elements as the process evolves over time. Therefore, the appropriate prediction of the structural lifetime depends directly of the prevision capacity of those effects over the behavior of the structural systems. In this work, a mechanical model that combines the corrosion effects over the reinforcement and the concrete and steel material nonlinear responses is proposed to predict the resistant loss of reinforced concrete beams over the time. The steel and concrete nonlinear behavior was modeled by model based on unidimensional plasticity theory and damage mechanics, respectively. The Fick’s laws and empirical methods based on the Faraday’s laws were used to represent chloride penetration inside concrete and reinforced degradation, respectively. A simplified process was adopted to simulate the corrosion beginning in different times over the structure. The results showed that the rate of loss resistant capacity of the analyzed beam is higher in the first years after the beginning of corrosion and tend to stabilized in subsequent years. Furthermore, the structural behavior is very sensitive regarding the considered corrosive effects in the analyses.
ResumoThis work aims to study the mechanical effects of reinforcement's corrosion in hyperstatic reinforced concrete beams. The focus is the probabilistic determination of individual failure scenarios change as well as global failure change along time. The limit state functions assumed describe analytically bending and shear resistance of reinforced concrete rectangular cross sections as a function of steel and concrete resistance and section dimensions. It was incorporated empirical laws that penalize the steel yield stress and the reinforcement's area along time in addition to Fick's law, which models the chloride penetration into concrete pores. The reliability theory was applied based on Monte Carlo simulation method, which assesses each individual probability of failure. The probability of global structural failure was determined based in the concept of failure tree. The results of a hyperstatic reinforced concrete beam showed that reinforcements corrosion make change into the failure scenarios modes. Therefore, unimportant failure modes in design phase become important after corrosion start.Keywords: reinforcements corrosion, chlorides ingress, Fick's law, reliability, reinforced concrete, failure scenarios.Este trabalho tem como principal objetivo analisar os efeitos da corrosão de armaduras em vigas em concreto armado na alteração dos possíveis cenários de falha individuais e na falha global da estrutura ao longo do tempo. As equações de estado limite consideradas descrevem analiticamente a resistência à flexão e ao esforço cortante em seções transversais retangulares em concreto armado. Foi também incorporada uma lei que penaliza a resistência ao escoamento do aço em função da evolução da corrosão em conjunto com a lei de Fick, a qual modela a penetração de íons cloreto no interior dos poros do concreto. Equações empíricas baseadas na lei de Faraday foram utilizadas para a determinação da nova área de armadura a cada instante de tempo na análise. A teoria da confiabilidade foi aplicada adotando-se o método de simulação de Monte Carlo para a avaliação das probabilidades individuais dos modos de falha considerados. A determinação da probabilidade de falha global da estrutura seguiu um procedimento baseado no conceito de árvore de falhas. Os resultados da análise de uma viga hiperestática em concreto armado demonstram que a corrosão das armaduras pode alterar os cenários de falha, de forma que, modos de falha não importantes na fase de projeto se tornam importantes à medida que o processo corrosivo evolui.Palavras-chave: corrosão de armaduras, ingresso de cloretos, leis de Fick, confiabilidade, concreto armado, cenários de falha.
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