Sustainable Maintenance and Repair of RC Coastal Structures

International audienceMany agencies worldwide have to manage structurally damaged reinforced concrete (RC) coastal infrastructure subjected to chloride ingress that require significant repairs. These repairs should ensure optimal levels of serviceability and safety and minimise costs and environmental impact. However, there is a wide quantity of protocols, techniques and materials for repair and there is no much information about their durability performance. This paper proposes a methodology for evaluating, comparing and/or improving sustainability of maintenance strategies. It was developed within the framework of the MAREO project in collaboration with the different stakeholders involved during the whole structural lifetime. It is based on probabilistic modelling of deterioration and repair, and the sustainability assessment considers costs (with conventional and intergenerational discounting), CO 2 emissions and waste generation. The methodology is illustrated with a numerical example aiming to evaluate and improve the sustainability of a repair technique for RC structures subjected to chloride-induced corrosion damage. Overall results indicate that sustainable solutions increase global costs but they could reduce significantly environmental impact

Optimizing the design of timber components under decay and climate variations

International audienceThe durability of timber structures can be affected by the isolated or combined actions of loading, moisture content, temperature, biological activity, etc. This work focuses on the optimal design of new timber structures subjected to deterioration. Since the deterioration processes and the structural behavior of timber structures are complex, nowadays the deterioration models are not able to account for all influencing factors. Consequently, this study is based on an empirical model that was derived based in-lab experimental studies for the decay growth of brown rot in pine sapwood under variant climate conditions. Such a model is divided into two processes: (i) activation process and (ii) mass loss process. On the other hand, there are significant uncertainties involved in the problem. The uncertainties inherent to materials properties, models and climate are considered throughout a time-dependent reliability based-design optimization (TD-RBDO) approach. The TD-RBDO aims to ensure a target reliability level during the operational life. This approach is applied to design optimization of a new timber component subjected to different French climates. The performance of the optimized solution is compared with a traditional cross-section designed according to the Eurocode 5 in terms of safety. The overall results indicate that an optimized solution ensures a target reliability level during the whole structural lifetime

Probabilistic lifetime assessment of RC structures under coupled corrosion-fatigue deterioration processes

International audienceStructural 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

Coupled reliability model of biodeterioration, chloride ingress and cracking for reinforced concrete structures

International audienceMaintaining 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

Probabilistic Evaluation of the Sustainability of Maintenance Strategies for RC Structures Exposed to Chloride Ingress

International audienceNowadays, 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

A Markov regime-switching framework to forecast El Niño Southern Oscillation patterns

International audienceThe El Niño-Southern Oscillation (ENSO) is an ocean-atmosphere phenomenon involving sustained sea surface temperature fluctuations in the Pacific Ocean, causing disruptions in the behavior of the ocean and atmosphere. We develop a Markov switching autoregressive model to describe the Southern Oscillation Index (SOI), a variable that explains ENSO, using two autoregressive processes to describe the time evolution of SOI, each of which associated with a specific phase of ENSO. The switching between these two models is governed by a discrete time Markov chain (DTMC), with time-varying transition probabilities. Then, we extend the model using sinusoidal functions to forecast future values of SOI. The results can be used as a decision-making tool in the process of risk mitigation against weather and climate related disasters

Influence of weather and global warming in chloride ingress into concrete: a stochastic approach

International audienceReinforced 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

Considération des champs spatiaux des propriétés du matériau dans l'optimisation de l'inspection et du contrôle des structures

L'aléa lié aux processus de dégradation et aux propriétés du matériau ainsi que le bruit des mesures font que l'inspection soit un défi majeur pour les maîtres d'ouvrage. Le but de cette étude est d'optimiser les inspections afin d'avoir des bonnes représentations de l'aléa d'un paramètre donné. On s'intéresse ici à la fiabilité d'une barre sous tension où le champ stochastique, modélisé par une expansion de Karhunen-Loève, représente sa résistance. On introduit un bruit de mesure simulé par une variable normale et on optimisera les inspections pour des différents niveaux de brui

System-level Maintenance Optimization for Power Distribution Systems Subjected to Hurricanes

Overhead electric power distribution systems are vulnerable to extensive damage due to hurricanes. Most of the damage is caused by the failure of distribution poles, which are mostly wood poles. As a natural material, wood is susceptible to strength deterioration over time due to decay. As such, utility companies carry out preventive maintenance actions to minimize the likelihood of failure of the poles due to decay and extreme events (hurricanes). Due to the scarcity of resources for maintenance, an optimization approach to maintenance planning is necessary. Most utilities consider minimizing maintenance cost as the objective in their wood pole maintenance planning. However, due to increasing demand for higher system reliability, the consideration of cost alone in maintenance optimization is not adequate. This paper presents a maintenance optimization framework for power distribution systems under hurricane hazard considering system performance as the objective. Two maintenance strategies are explored: periodic chemical treatment and the use of fiber reinforced polymer (FRP). The distribution system of a virtual city assumed to be located in Florida is used to demonstrate the framework

Probabilistic characterization of uncertainties and spatial variability of material properties from NDT measurements

La maintenance optimale des structures vise à garantir des niveaux minimales de fiabilité et capacité de service en réduisant le nombre d’inspections et de réparations durant la vie utile de l’ouvrage. A fin d’optimiser le planning de maintenance, une réévaluation de la structure existante est nécessaire pour la mise-à-jour des propriétés du matériau et/ou l’état de dégradation de la structure. Les inspections donnent des informations importantes pour cette réévaluation. Les inspections peuvent se appuyer sur des techniques d’auscultation destructives ou de contrôle non destructif (CND). Les résultats issus de techniques semi-destructives ou destructives donnent généralement des valeurs très fiables. Par contre, ils sont couteaux et ne peuvent pas s’effectuer en grand nombre afin de caractériser les incertitudes et la variabilité spatiale des variables d’intérêt. Dans d’autres cas, les difficultés d’accès aux zones d’inspection, privilégient le choix de méthodes CND. A nos jours, des nombreuses études modélisent l’incertitude des propriétés/quantités d’intérêt à l’aide de variables aléatoires et sa variabilité spatiale de par des champs stochastiques. Les incertitudes et sa variabilité spatiale peuvent se caractériser à partir d’inspections CND. Par conséquent, nous proposons ici une méthode pour optimiser la localisation et le nombre d’inspections sous contrainte de la qualité de l’inspection. La caractérisation peut avoir lieu à partir d’un ensemble de mesures expérimentales provenant des campagnes d’inspection où les paramètres mesurés sont des propriétés du matériau et/ou une quantité d’intérêt. Nous supposons que le type de distribution et la nature du champ aléatoire sont connus et nous cherchons à caractériser leurs paramètres. La méthode proposée a été illustrée en étudiant plusieurs cas pratiques où il existe des limitations dans longueur et/ou dans le nombre d’éléments. Les résultats indiquent qu’il y a des configurations d’auscultation optimales qui améliorant la caractérisation de l’aléa et la variabilité spatiale des quantités d’intérêt