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International audience; Corrosion induced by chloride ions has become a critical issue for many reinforced concrete structures. The chloride ingress into concrete has been usually simplified as a diffusion problem where the chloride concentration throughout concrete is estimated analytically. However, this simplified approach has several limitations. For instance, it does not consider chloride ingress by convection which is essential to model chloride penetration in unsaturated conditions as spray and tidal areas. This paper presents a comprehensive model of chloride penetration where the governing equations are solved by coupling finite element and finite difference methods. The uncertainties related to the problem are also considered by using random variables to represent the model's parameters and the materials' properties, and stochastic processes to model environmental actions. Furthermore, this approach accounts for: (1) chloride binding capacity; (2) time-variant nature of temperature, humidity and surface chloride concentration; (3) concrete aging; and (4) chloride flow in unsaturated conditions. The proposed approach is illustrated by a numerical example where the factors controlling chloride ingress and the effect of weather conditions were studied. The results stress the importance of including the influence of the random nature of environmental actions, chloride binding, convection and two-dimensional chloride ingress for a comprehensive lifetime assessment.

International audience; The modeling of in-service behavior is of first importance when reassessing complex structures like harbor structures and when performing risk analysis. To this aim, the monitoring of structures allows assessment of the level of loading and to provide more realistic models for mechanical behavior or input values for their parameters. Moreover, for complex structures and due to building hazards, a stochastic modeling is needed to represent the large scatter of measured quantities. In this article, a step-by-step procedure for structural identification is presented. A decomposition of random variables on Polynomial Chaos is selected and it is shown to represent better the basic variables in comparison to preselected distribution functions, when considering maximum likelihood estimate. The decomposed variables are used for a stochastic analysis to be further updated with available monitoring data. The model can be used to follow the structure behavior during in-service or extreme conditions and to perform a reliability analysis. The proposed procedure will be carried out by using available data from the monitoring of a pile-supported wharf in the Port of Nantes, in France, but it can be generalized to similar monitored structures.

International audience; A probabilistic analysis of the face stability of a tunnel driven by a compressed-air pressurized shield is presented. The collocation-based stochastic response surface methodology (CSRSM) is used. The deterministic model employed in the probabilistic analysis is analytical. A translational multiblock collapse mechanism in the framework of the kinematic theorem of limit analysis forms the basis of the analysis. The soil friction angle and cohesion are considered as random variables. CSRSM was first validated by the comparison of the results obtained from the original analytical deterministic model. Then, the influence of the probabilistic characteristics of the uncertain variables was studied. Contrary to the correlation between c and phi and the coefficients of variation of these variables, which have a significant effect on the variability of the critical collapse pressure, the nonnormality of the distributions of the random variables was shown not to have a considerable effect on the distribution of the output.

International audience; This paper proposes High Dynamic Range (HDR) imaging as a protocol for nondestructive-testing for the first time. HDR imaging protocol has been experimentally validated on images of pitting corrosion in this paper and has been further applied to isolate a range of image backgrounds that arise out of a number of environmental conditions. The superiority of HDR imaging over a standard imaging process has been demonstrated. The results indicate that the proposed protocol is not limited by the examples considered in this paper and can readily be applied to a number of infrastructure maintenance management related applications. The protocol complements and improves standard visual inspection techniques and expert opinions. This approach immediately lends itself to further mathematical and statistical analyses, both qualitative and quantitative.

International audience; The aim of this paper is to determine the collapse and blow-out face pressures of a circular tunnel driven by a pressurized shield. The analysis is performed in the framework of the kinematical approach of the limit analysis theory. Two rotational failure mechanisms are proposed for the active and passive cases. These mechanisms have two significant advantages with respect to the available ones: (i) they take into account the entire circular tunnel face instead of an inscribed ellipse to this circular area, and (ii) they are more consistent with the rotational rigid-block movement observed in the experimental tests. For both the active and passive cases, the three-dimensional failure surface was generated 'point by point' instead of simple use of the existing standard geometric shapes such as cones or cylinders. This was achieved by employing a spatial discretization technique. The numerical results have shown that the present rotational mechanisms provide, in the case of frictional soils (with or without cohesion), a significant improvement with respect to the translational mechanisms. Finally, an extension of the proposed collapse mechanism to include a tension cut-off in the classical Mohr-Coulomb failure criterion is presented and discussed.

International audience; The scope of this work is the determination of single-crystals elastic constants (SEC) from X-ray diffraction lattice strains measurements performed on multi-phase polycrystals submitted to mechanical load through a bending device. An explicit three scales inverse selfconsistent model is developed in order to express the SEC of a cubic phase, embedded in a multiphase polycrystal, as a function of its X-ray Elasticity Constants. Finally, it is applied to a twophases (α+β) titanium based alloy (Ti-17), in order to estimate Ti-17 β-phase unknown SEC. The purpose of the present work is to account the proper microstructure of the material. In particular, the morphologic texture of Ti-17 α-phase, i.e. the relative disorientation of the needle-shaped grains constituting this phase, is considered owing to the so-called Generalized Self-Consistent model.

A new two-dimensional 2D limit analysis failure mechanism is presented for the determination of the critical collapse pressure of a pressurized tunnel face in the case of a soil exhibiting spatial variability in its shear strength parameters. The proposed failure mechanism is a rotational rigid block mechanism. It is constructed in such a manner to respect the normality condition of the limit analysis theory at every point of the velocity discontinuity surfaces taking into account the spatial variation of the soil angle of internal friction. Thus, the slip surfaces of the failure mechanism are not described by standard curves such as log-spirals. Indeed, they are determined point by point using a spatial discretization technique. Though the proposed mechanism is able to deal with frictional and cohesive soils, the present paper only focuses on sands. The mathematical formulation used for the generation of the failure mechanism is first detailed. The proposed kinematical approach is then presented and validated by comparison with numerical simulations. The present failure mechanism was shown to give results in terms of critical collapse pressure and shape of the collapse mechanism that compare reasonably well with the numerical simulations at a significantly cheaper computational cost. DOI: 10.1061/ASCEEM.1943-7889.0000196 CE Database subject headings: Tunnels; Limit analysis; Failures; Shear strength; Parameters. Author keywords: Tunnels; Active pressure; Limit analysis; Spatial variability; Local weakness.

National audience; La gestion des infrastructures est souvent basée sur des critères économiques. Cette étude propose une extension à des critères environnementaux : la génération de déchets et le dégagement de dioxyde de carbone. On s'intéresse à l'optimisation de la maintenance et de la réparation de structures en béton armé placées en ambiance maritime. Afin de modéliser les effets de l'inspection et de la maintenance, nous utilisons des processus de Markov et la théorie de la décision. Nous identifions les paramètres des chaines de Markov à partir de simulations de Monte Carlo d'un modèle stochastique de dégradation. Enfin, nous proposons une analyse multicritères pour l'évaluation de l'impact environnemental des stratégies de maintenance.

Nowadays, multiple constraints imposed by economic, social and environmental considerations undergo maintenance planning optimization into a major challenge to designers, owners and users of infrastructure. This study focuses on the management of reinforced concrete (RC) structures placed in marine atmospheres. Under these exposure conditions, chloride penetration generates corrosion of the reinforcing bars reducing the RC durability. Therefore, modeling the deterioration process as well as the maintenance actions carried out during the operational life becomes paramount for the formulation of a sustainable maintenance strategy. The main objective of this thesis is to develop a new methodology for optimizing the performance of maintenance strategies for corroding RC structures. Contrary to classical management of infrastructure that is mainly based on economic constraints, this study proposes an extension to environmental criteria in view to find sustainable maintenance solutions. The management model combines: a comprehensive model of chloride penetration, Markov processes and decision theory. The uncertainty related to material properties, model and environmental actions as well as the effect of imperfect inspections are also integrated to the model. Given that a sustainable maintenance strategy should minimize costs and environmental impact, a multi-criteria approach for decision-making is also implemented. Several numerical examples and real case studies illustrate the aforementioned points throughout the manuscript. In general, it is concluded that the proposed methodology can be useful to improve the environmental performance and the costs of a given strategy by ensuring appropriate levels of serviceability and safety.; A l'heure actuelle, des multiples contraintes économiques, sociales et environnementales transforment l'optimisation de la planification des travaux de maintenance en un défi majeur pour les concepteurs, les propriétaires et les utilisateurs des infrastructures. Cette étude se concentre sur la gestion des structures en béton armé placées dans des environnements marins. Dans ces conditions d'exposition, la pénétration des ions chlorure génère la corrosion des armatures en réduisant la durabilité du béton armé. Par conséquent, la modélisation des processus de dégradation ainsi que des actions de maintenance réalisées au cours de la durée de vie opérationnelle devient primordiale pour la formulation d'une stratégie de maintenance durable. L'objectif principal de cette thèse est de développer une nouvelle méthodologie pour l'optimisation de la performance des stratégies de maintenance des structures en béton armé sujettes à la corrosion. La gestion des infrastructures est principalement basée sur des contraintes économiques. Cette étude propose une extension à des critères environnementaux pour trouver des solutions inscrites dans le cadre du développement durable. Le modèle de gestion combine: un modèle étendu de pénétration des chlorures, des processus de Markov et la théorie de la décision. L'aléa lié aux propriétés des matériaux, au modèle et aux actions environnementales ainsi que les effets des inspections imparfaites sont également intégrés au modèle. Étant donné que la stratégie de maintenance durable doit minimiser les coûts et l'impact environnemental, une approche multicritère pour la prise de décision est également mise en œuvre. Plusieurs exemples numériques et des études de cas réels illustrent les points ci-dessus dans ce mémoire. Il est démontré que la méthode proposée peut être utile pour améliorer la performance environnementale et les coûts d'une stratégie de maintenance donnée en assurant des niveaux appropriés de service et de sûreté.

International audience; Reinforced concrete (RC) structures are subject to environmental actions affecting their performance, serviceability and safety. Among these actions, chloride ingress leads to corrosion and has been recognized as a critical factor reducing the service life of RC structures. This paper presents a stochastic approach to study the influence of weather conditions and global warming on chloride ingress into concrete. The assessment of chloride ingress is carried out on the basis of a comprehensive model that couples the effects of convection, chloride binding, concrete aging, temperature and humidity. A simplified model of temperature and humidity including seasonal variations and global warming is also proposed in this work. Three scenarios of global warming are defined based on: gas emissions, global population growth, introduction of new and clean technologies and use of fossil sources of energy. The proposed approach is illustrated by a numerical example where it is found that the climate changes may yield to significant lifetime reductions. These results justify the implementation of countermeasures directed to (1) reduce and/or mitigate the action of global warming on weather and (2) minimize the impact of climate changes on RC structures.

International audience; Nowadays, multiple constraints imposed by economical, social and environmental considerations undergo maintenance planning optimization into a major challenge to designers, owners and users of infrastructure. This study presents a simplified methodology to evaluate the sustainability of maintenance strategies used in reinforced concrete structures exposed to chlorides. The proposed approach is illustrated throughout the paper with an application to large-scale maintenance of a real structure (Agri-foodstuffs terminal wharf). The repair strategy consists of demolition of the polluted concrete and rebuilding of cover by using three techniques (wet shotcrete, dry shotcrete and formed concrete). The repair times are estimated by taking the randomness of chloride ingress into account. Three criteria are used to evaluate the sustainability of the repair techniques: present value life-cost, waste production and CO2 emissions. Based on this multi-criteria comparison, a simplified decision-making scheme based on a multi-objective index is proposed.

Durability of reinforced concrete (RC) structures placed in non-aggressive environments is often sat- isfactory. However, under certain environmental conditions there are internal or external actions that significantly reduce their lifetime. Nowadays, lifetime assessment of deteriorating structures is focused on the isolated effect of the main deterioration processes (corrosion, fatigue, creep, etc.). However, it is paramount to study the combined effect of various deterioration processes because such interaction could reduce structural integrity. This study proposes a new model for lifetime assessment of RC structures subjected to corrosion- fatigue deterioration processes. The proposed model distinguishes between the following phenomena: chloride penetration, corrosion of reinforcement, concrete cracking and corrosion-fatigue of reinforcing bars. Chloride penetration determines corrosion initiation. Corrosion reduces the cross-section of reinforcing steel. The accumulation of corrosion products in the steel/concrete interface produces concrete cracking. Fatigue causes the nucleation and the propagation of cracks in steel bars. The interaction between corrosion and fatigue can only be taken into account when modeling the combined problem. Thus, pitting corrosion generates stress concentrations that nucleate cracks in the reinforcing bars. Cyclic loading and environmental factors affect the kinematics of crack propagation. There exists significant uncertainty related to the combined corrosion-fatigue problem. This study also addresses this problem by considering the uncertainty inherent in (1) material properties, (2) model and its parameter and (3) environmental actions. Time-invariant random variables represent the uncertainty of material properties and model. Stochastic processes consider the uncertainty of environmental actions. The proposed stochastic models for weather (temperature and humidity) take into account seasonal variations and global warming. The stochastic models for environmental chloride concentration differentiate between exposure to de-icing salts or the sea. Finally, a fuzzy approach accounts for the uncertainty related to corrosion rate. The proposed model is applied to the reliability analysis of RC members located in various chloride- contaminated environments. Overall results reveal that the combined effect of corrosion-fatigue de- pends on environmental conditions and strongly influences the performance of RC structures leading to large reductions in expected lifetime.

International audience; Structural deterioration is becoming a major problem when considering long term performance of infrastructures. The existence of a corrosive environment, cyclic loading and concrete cracking cause structural strength degradation. The interaction of these conditions can only be taken into account when modeling the coupled action. In this paper, a new model to assess lifetime of RC structures subject to corrosion-fatigue deterioration processes, is proposed. Separately, corrosion leads to cross section reduction while fatigue induces the nucleation and the propagation of cracks in steel bars. When considered together, pitting corrosion nucleates the crack while environmental factors affect the kinematics of crack propagation. The model is applied to the reliability analysis of bridge girders located in different chloride-contaminated environments. Overall results show that the coupled effect of corrosion-fatigue on RC structures affects strongly its performance leading to large reduction in the expected lifetime.

International audience; The French harbour system has an essential role: on the one hand for French business, tourism and industry; and on the other hand for European defence. Consequently, maintenance of harbour assets is a stake of major importance.This paper focuses on the analysis of actual maintenance practices, associated constraints, but also capacities to fulfil maintenance programs of the built assets of French harbour owners. The needs in risk management and control are also highlighted. The results are presented by focusing the analysis on observed levels of heterogeneity.; Le système portuaire français joue un rôle essentiel : d'une part pour l'économie française, le tourisme et l'industrie, et d'autre part pour la défense européenne. En conséquence, la maintenance du patrimoine portuaire représente un enjeu de tout premier plan. Cet article se focalise sur l'analyse des pratiques actuelles de maintenance, des contraintes associées, mais aussi des capacités des gestionnaires des ports français à respecter les programmes de maintenance établis. Les besoins en termes de gestion et de maîtrise des risques sont aussi soulignés. Les résultats sont présentés en portant une attention particulière aux niveaux d'hétérogénéité observés.

International audience; Maintaining and operating civil infrastructure systems has been recognized as a critical issue worldwide. Among all possible causes of safety reduction during the structural lifetime, deteriora- tion is particularly important. Structural deterioration is usually a slow time-dependent process controlled by safety and operation threshold specifications. This paper presents a model of RC deterioration by coupling biodeterioration (i.e., chemical, physical and mechanical action of live organisms), steel corrosion, and concrete cracking. The final purpose of the model is to compute the reduction of the concrete section and the area of steel reinforcement in order to assess the change of structural capacity with time. Given the uncertainties in both the parameters and the model, the probabilistic nature of loads, the material properties and the difussion process are taken into account to evaluate structural reliability. The model is illustrated with an example where the inelastic behavior of a pile subject to random loading is considered. The results of the analysis have shown that the effect of biodeterioration on the structural performance is significant and can cause an important reduction of its lifetime. On the whole, the paper states that modeling the effects of biodeterioration in RC structures should be included as part of infrastructure planning and design, especially, when they are located in aggressive environments.

International audience; Quantitative data from inspections are necessary to determine the state of a deteriorating structure and to identify the optimal maintenance strategy for the remaining life of the structure. This article presents the development of a two-stage inspection based maintenance management framework, which provides the owner/manager of a structure with a decision tool to optimise the service life costs of a structure. The two stages of an inspection are considered here, detection of defects present and sizing of detected defects. Using this framework, the optimal inspection interval for this study, based on the minimisation of the service life costs, is determined and the effect of inspection quality of the two techniques is studied. By modelling the detection and sizing stage of an inspection separately, the optimum combination of techniques can be determined.

International audience; A reliability-based analysis of a strip foundation subjected to a central vertical load is presented. Both the ultimate and the serviceability limit states are considered. Two deterministic models based on numerical simulations are used. The first one computes the ultimate bearing capacity of the foundation and the second one calculates the footing displacement due to an applied load. The response surface methodology is utilized for the assessment of the Hasofer–Lind reliability indexes. Only the soil shear strength parameters are considered as random variables while studying the ultimate limit state. Also, the randomness of only the soil elastic properties is taken into account in the serviceability limit state. The assumption of uncorrelated variables was found to be conservative in comparison to the one of negatively correlated variables. The failure probability of the ultimate limit state was highly influenced by the variability of the angle of internal friction. However, for the serviceability limit state, the accurate determination of the uncertainties of the Young’s modulus was found to be very important in obtaining reliable probabilistic results. Finally, the computation of the system failure probability involving both ultimate and serviceability limit states was presented and discussed.

International audience; This paper deals with a national investigation within the GEROM project that aims to analyse the patrimony of harbours owners and the actual practice of maintenance. Results are analysed with a special care to the use in risk analysis and a risk analysis is applied to a lock for illustration.; Cet article présente une enquête menée au sein du projet GEROM et visant à questionner les exploitants de structures portuaires sur leur patrimoine et leurs pratiques actuelles de maintenance. Les résultats sont commentés avec un angle « analyse de risque » et l’illustration d’une analyse de risque quantitative est proposée sur une écluse.

International audience; In structural analysis, stochastic finite element methods offer a robust tool to deal with randomness on material properties or loadings. Unfortunately, there is still no available efficient strategy to deal with uncertainties on the geometry. Here, we bring an answer to this problem by proposing a new method based on an extension to the stochastic framework of the eXtended Finite Element Method (X-FEM). This method lies on three major points : the implicit description of geometry by the level-set technique, the use of Galerkin approximation at space and stochastic levels and the use of the partition of unity method for the enrichment of the finite element approximation space.; Les méthodes éléments finis stochastiques offrent un outil robuste pour la prise en compte dans le calcul de structure des aléas sur les propriétés matériau et les chargements. L’aléa portant sur la géométrie reste cependant un point mal maîtrisé dans le cadre de ces techniques. Afin de répondre à cette problématique, nous proposons une nouvelle méthode basée sur une extension de la méthode éléments finis étendus (X-FEM) au cadre stochastique. Cette méthode repose sur trois points : la description implicite de la géométrie par des level-sets aléatoires, l’utilisation d’une approximation de Galerkin au niveau stochastique et spatial et l’utilisation de la méthode de la partition de l’unité pour l’enrichissement de l’espace d’approximation.

International audience; Inflatable structures are under increasing development in various domains. Their study is often carried out by using 3D membrane finite elements and for static loads. There is a lack of knowledge in dynamic conditions, especially for simple and accurate solutions for inflatable beams. This paper deals with the research on the natural frequencies of inflatable Timoshenko beams by an exact method: the continuous element method (CEM), and by the classical finite element method (FEM). The dynamic stiffness matrix D(ω) is here established for an inflatable beam; it depends on the natural frequency and also on the inflation pressure. The stiffness and mass matrixes used in the FEM are deduced from D(ω). Natural frequencies and natural modes of a simply supported beam are computed, and the accuracy of the CEM is checked by comparisons with the finite element method and also with experimental results.

International audience; Owners of structures and infrastructure base their maintenance decision schemes mainly on structural integrity assessment and consequence analysis. The major inputs come from information collected by inspections employing non-destructive or destructive tools. Uncertainties and errors of measurement can lead to bad decisions but these effects are rarely integrated into the decision making process. Risk Based Inspection (RBI) provides the basics for optimizing the maintenance plans of existing structures while ensuring satisfactory safety and availability of the structure during its service life. This basis depends both on computation of reliability index and probabilistic modeling of inspection results. Probabilistic modeling of inspection results leads to specifying the Probability of Detection (PoD), the Probability of False Alarms (PFA) and the Receiver Operating Characteristics (ROC) curve that are usually considered as key parameters in RBI. Under these circumstances the comparison of Non destructive Testing (NDT) tools in terms of cost/benefit is difficult to be established as well as the method for optimizing a given technique. This paper starts from the αδ method that gives a new performance indicator in this context, and apply it to the field of inspection of steel harbor structures, after a detailed analysis of uncertainties during corrosion assessment by ultrasonic measurements.; Les gestionnaires de structures et d’infrastructures fondent leurs décisions de maintenance sur des analyses d’intégrité structurelle et des conséquences de défaillances. Les entrées principales de ces méthodes sont les inspections par contrôles destructifs ou non destructifs. Les erreurs de mesure peuvent conduire à de mauvaises décisions, celles-ci étant rarement prises en compte dans les analyses de risque. Les méthodes d’inspection basées sur les analyses des risques fournissent le cadre méthodologique d’optimisation des inspections. Les résultats dépendent de l’évaluation de la fiabilité et de la modélisation probabiliste des données d’inspection. Cette dernière est généralement basée sur l’évaluation des Probabilités de Détection, Probabilités de Fausses Alarmes et Courbes ROC. Au vu de la difficulté d’une évaluation précise de ces grandeurs, il reste difficile de disposer des outils d’optimisation du rapport coût/bénéfice ou de comparaison des techniques. Cet article s’appuie sur la méthode αδ qui fournit un indicateur de performance dans ce contexte appliqué au contrôle de la corrosion de palplanches métalliques; on décrit et modélise en particulier les incertitudes de mesure par ultrasons selon différents protocoles.

International audience; Maintenance and management policies are usually focused on minimizing the life-cycle cost only. Therefore the optimal solution in this context does not necessarily result in a satisfactory long-term structural performance. In this paper, we will present an approach for modeling the degradation of structures and infrastructures for maintenance purposes. The degradation is modeled using probabilistic data-driven state dependent stochastic processes, hereafter called meta-model. This work implements this degradation model into a maintenance framework and carries out two numerical examples in order to show the applicability of our meta-model in a maintenance and management optimization context. This paves the road for future work on meta-model updating and maintenance optimization by considering a multi-objective optimization policies.

International audience; Measuring the true extent of damage in a structure remains a difficult task for inspectors. For visual inspections, an accurate assessment of the damage state is often subjective in nature and prone to error, especially when an inspection is conducted in hostile surroundings or when there are challenging environmental conditions present. While incorporating some form of Non-Destructive Technique (NDT) is generally useful for the inspection process, its performance may similarly degrade in the presence of environmental conditions. It is thus of great practical importance to have a measure of the performance of an NDT for a host of varying conditions, thereby allowing the inspector to determine whether it could be successfully applied in a given situation. In this paper, a measure of the effectiveness of an NDT technique is probabilistically determined for various environmental conditions through the use of Receiver Operating Characteristic (ROC) curves. ROC curves offer a convenient way of characterising and comparing the performance of an NDT under various conditions. The NDT considered in this paper is an image processing based damage detection technique which uses texture information in conjunction with Support Vector Machine (SVM) classification to identify damaged regions. The variability of this technique is evaluated for various damage forms that are subjected to two changing parameters; turbidity and lighting. There were three set levels (low, medium, high) for each parameter. The conditions that were conducive to good detection were isolated and ranked using the α-δ method as part of the ROC analysis. The technique is applied to standard dynamic range (SDR) images and high dynamic range (HDR) images in order to assess their respective sensitivities to the changing parameters.

International audience; The El Niño-Southern Oscillation (ENSO) is an ocean – atmosphere phenomenon that involves sustained sea surface temperature fluctuations in the Pacific Ocean. This causes disruption in the behavior of the ocean and the atmosphere having important consequences on the global weather. This paper develops a stochastic model to describe El Niño-Southern Oscillation patterns. A Markov Switching Autoregressive model (MS-AR) was implemented to fit the Southern Oscillation Index (SOI), a variable that explains the phenomenon. The model consists of two autoregressive processes describing the time evolution of SOI, each of which associated with a specific phase of ENSO (El Niño and la Niña). The switching between these two models is governed by a discrete time Markov chain. We study the advantages of incorporating time-varying transition probabilities between them and show that the fitted model provides an adequate description of the time series, and demonstrate its utility in analysis and evaluation of the phenomenon