Étude numérique de la capacité résiduelle d'un tablier de pont existant : évaluation de la fiabilité structurale sans et avec réparation en BFUP

«RÉSUMÉ:L’étude du comportement d’ouvrages existants soumis à des conditions d’utilisation réelles permet de mieux comprendre les mécanismes d’usure et de défaillance. La récente déconstruction d’un pont au Québec fournit une rare occasion d’étudier la fiabilité structurale d’un système complexe en fin de vie utile. L’objectif principal de cette étude est l’évaluation de la capacité résiduelle du système structural de tablier de façon probabiliste et d’étudier l’effet d’une réparation par une couche de béton fibré à ultra haute performance (BFUP) disposée au-dessus des poutres et des dalles intercalaires. Une approche numérique sophistiquée basée sur des analyses non-linéaires en éléments finis 3D est utilisée. La modélisation 3D du tablier permet une redistribution des charges dans l’ensemble du système structural composé de plusieurs éléments redondants comme les poutres. Le modèle implique plus de 700 000 degrés de liberté, considère des lois de comportement non-linéaires pour les matériaux et pour la configuration avec réparation, il tient compte d’une interface de contact cohésive entre béton et couche de BFUP. L’étude de la corrosion, basée sur les données des plus récents rapports d’inspection, indique une forte influence de la distribution de la corrosion au sein du tablier.»

Abstract

«ABSTRACT: Studying the behavior of existing structures under real-life conditions provides a better understanding of wear and failure mechanisms. The recent deconstruction of a bridge in Quebec provides a rare opportunity to study the structural reliability of a complex system at the end of its service life. The main objective of this study is to probabilistically assess the structural capacity of the deck, and to investigate the effect of a top layer reinforcement using ultra-high-performance fiber-reinforced concrete (UHPFRC) placed above the girders and spacer slabs. A sophisticated numerical approach based on non-linear 3D finite element analysis is used. The 3D modeling of the deck enables load redistribution throughout the structural system, which is made of several redundant elements such as beams and transverse diaphragms. The model involves over 700,000 degrees of freedom, considers non-linear constitutive laws for the materials and, in the final phase of this research, considers a cohesive contact interface between concrete and UHPFRC layer. The corrosion study, based on data from the most recent inspection reports, indicates a strong influence of corrosion distribution within the deck. To incorporate the probabilistic aspect of the results, the Rosenblueth point estimation method is used, due to its convenience for assessing mean and variance or resistance, using complex analysis tools. To assess the residual deck capacity, two new approaches for evaluating existing bridges are tested. The first approach (intermediate level) uses the overall safety factor concept, while the second (advanced level) is based on the target reliability index. The probabilistic study without repair yielded somewhat different conclusions with both the intermediate and advanced levels approaches. A smaller capacity-to-demand ratio was achieved with the intermediate approach, making it more conservative. For most of probabilistic analyses in the unrepaired condition, the final failure mode was a combined flexural-shear failure involving the edge beam and a number of adjacent beams mobilized by the slabs and diaphragms. The ultimate limit of prestressing steel has never been reached. The probabilistic study with UHPFRC repair was performed only with the advanced level methodology. The addition of a 50 mm repair layer increases the bridge’s live load capacity factor by 16%. The failure mechanism remains almost the same as in the case without repair. Evidence of damage to the repair interface at mid-span and in the vicinity of the edge beam appears to be visible near the failure but did not primarily contribute to the failure. There was little evidence of damage to the UHPFRC layer. All Rosenblueth analyses (with or without repair) showed that the corrosion level in the cables was by far the most influential random variable on the strength of the deck.»