Jean-Louis Tailhan

Influence of accelerated corrosion on the reinforced cover concrete cracking behavior: experimental and numerical study

This article aims to present both experimental and numerical studies of the corrosion induced cracking pattern evolution of a reinforced concrete sample subjected to accelerated corrosion. The beam was not mechanically loaded. Rebars were intentiostatically corroded using a current density of 100μA/cm² of steel, in a chloride pond and for a 30 day period. Electrochemical tests and visual inspections were carried out in order to characterise the rebar state. Width evolution of the main longitudinal cover crack was measured thanks to ball-extensometer. A numerical modeling of the corroded RC beam has also been realised. The experimental and numerical results are in good agreement confirming the efficiency of the proposed modelling Cet article présente les principaux résultats d’une étude combinant approches expérimentale et numérique appliquées à un essai de corrosion accélérée sur un corps d’épreuve en béton armé. Ces résultats portent sur le suivi et la prédiction de l’évolution de la fissuration du béton sous l’effet de l’expansion des produits de corrosion. L’éprouvette n’a pas été chargée mécaniquement. Les armatures ont été corrodées en imposant un courant de densité de 100μA/cm² d’acier dans une solution saline pendant 30 jours. Des essais de caractérisation électrochimique ont été réalisés puis complétés par des inspections visuelles en vue de décrire l’état de dégradation de l’interface acier/béton. Les résultats de la simulation numérique conduisent à une évaluation satisfaisante de l’évolution de la fissure principale démontrant ainsi la pertinence de la modélisation proposée

Creep Behavior of a SFRC Under Service and Ultimate Bending Loads

A research project was carried out to evaluate the flexural creep behaviour of SFRC beams under sustained service loads and the crack propagation under high sustained loads. The evolution of the deflection, the crack width and the crack propagation were measured in service conditions (CMOD ws = 0.1 mm, load level P/Ps = 60 %) and ultimate conditions (wu = 0.5 mm, P/Pu = 60–90 %). The results allowed assessing the impact of the initial CMOD and sustained load levels on creep, crack propagation, damage evolution, and the mechanisms leading to the rupture of the beams. In service conditions, the results show that the deflection and crack opening of SFRC beams under sustained loading stabilises quickly toward an asymptote and that the compliance remains constant. In ultimate conditions, the results show that crack propagation governs the failure mechanisms of SFRC beams subjected to high sustained load levels. Moreover, it was observed that the beams failure occurs when the state of damage defined by the static behaviour envelope is attained.

A Probabilistic Explicit Cracking Model for Steel Fibres Reinforced Concretes (SFRC)

SFRC is increasingly used for structural applications. The present paper is devoted to a probabilistic explicit cracking model developed since 1985. It is used to analyze the cracking behaviour of different SFRC beams submitted to different loading conditions: bending and shear. It is demonstrated that this numerical model is fully capable to provide precise information about the cracking process related to this types of structural behaviour, especially concerning the cracks opening evolution.

Numerical Strategy for Developing a Probabilistic Model for Reinforced Concrete Structures (PMRCS)

This paper introduces a new approach to model cracking processes in large reinforced concrete structures, like dams or nuclear power plants. For these types of structures it is unreasonable, due to calculation time, to explicitly model rebars and steel-concrete bonds. To solve this problem, we developed, in the framework of the finite element method, a probabilistic macroscopic cracking model based on a multi-scale simulation strategy: the Probabilistic Model for Reinforced Concrete Structures (PMRCS). The PMRCS’s identification strategy is case-specific because it holds information about the local behaviour, obtained in advance via numerical experimentations. This information is then projected to the macroscopic finite element scale via inverse analysis. The Numerical experimentations are performed using a validated cracking model allowing a fine description of the cracking processes. The method used in the inverse analysis is inspired from regression (supervised learning) algorithms: data on the local scale – the training data coupled with working knowledge of the mechanical problem – would shape the macroscopic model. Although the identification phase can be relatively time-consuming, the structural simulation is as a result, very fast, leading to a sensitive reduction of the overall computational time. A first validation of this multi-scale modeling strategy is performed on a reinforced concrete slab-beam subjected to 3 point bending. We achieved promising results in terms of global behaviour and macro-cracking (mainly crack openings), and an important reduction in calculation time – up to 99% reduction! So we believe this is a promising approach to solve bigger and more complex structures in shorter time.

Macrocrack Propagation in a Concrete Specimen Subjected to a Sustained Loading: Influence of Tensile Creep

Structures managers need a better prediction of the delayed failure of concrete structures, especially for very important structures like nuclear power plant encasement. Sustained loadings at high level (above 75% of loading capacity of the structure), can lead to structure failure after some time. In this study, a series of 4point bending tests were performed in order to characterize the creep behaviour of pre-cracked beams under high load level. The specimens were made of normal strength concrete. A power law relationship is observed between the secondary deflection creep rate and the failure time. It is also shown that when crack propagation occurs during the creep loading, the creep deflection rate increases with the creep loading level and with the crack propagation rate. INTRODUCTION The delayed failure of concrete structures under sustained loading has been an important issue for researchers and structure managers for a long time. Among other topics, the progression to failure of a structure with a localized macrocrack, subjected to a sustained loading, needs a better understanding. In the past some researchers worked on the interaction between crack propagation and time dependence behaviour of concrete (Rusch (1960), Smadi et al. (1985), Rossi (1989), Rossi and Boulay (1990), Bazant and Gettu (1992), Zhou (1992), Carpinteri et al. (1997), Denarie (2000), Mazzotti and Savoia (2002), Denarie et al. (2006), Omar et al. (2009)). The scientific objective of the present work is to understand the physical mechanisms involved in the possible coupling between crack propagation and delayed behaviour of concrete. The industrial objective is more concerned with the case of the containment vessel of a nuclear power plant. As regards nuclear civil engineering, safety requirements specify durability of