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International audience; Chloride-induced corrosion is one of the main causes leading to the lifetime reduction of reinforced concrete (RC) structures in marine environments or subjected to de-icing salts. Modeling chloride ingress into concrete in a comprehensive way is therefore a crucial task to evaluate corrosion initiation risk and carry out preventive maintenance. Nevertheless, this comprehensive modeling is a challenging task that requires solving simultaneously a set of coupled non-linear partial differential equations. This task becomes more complex if the inherent uncertainties of the process are considered for probabilistic lifetime assessment. The present research aims to assess the probability of corrosion initiation of RC structures. The polynomial chaos expansion (PCE) method is employed to propagate uncertainties in a chloride ingress model requiring significant computational time to perform one deterministic simulation. PCE is also applied to perform a sensitivity analysis to determine which are the more influential random variables in the problem. The proposed methodology is applied to RC structures placed in several locations in France (Brest, Marseille, and Strasbourg) and subjected to realistic environmental conditions including climate change. The results show that the PCE-based model is accurate and efficient for lifetime assessment of RC structures subject to chloride-induced corrosion.

International audience; Floating offshore wind farms have become a gateway to reach locations that are technically and economically infeasible to exploit using fixed platforms. However, the high capital investments and the uncertainty associated with the reliability, capacity factor, technology evolution, electricity demand, and regulatory frameworks negatively affect the cost of energy of this approach. Alternative strategies, such as designing for flexibility, have been shown to increase the value of engineering systems subject to highly uncertain environments. In this article, an analysis based on life-cycle costs and Monte-Carlo simulation is used to determine if floating wind farms with flexible installed capacity result in lower costs of energy than traditionally designed wind farms. Flexibility is introduced using an adaptable platform strategy and an over-dimensioned platform strategy. The results show that the adaptable platform strategy has the potential to reduce the cost of energy up to 18% by increasing the energy generation and the lifetime of some components of the wind farm. Nonetheless, the benefits of flexibility depend on new legislation that allows for lifetime extensions and proper flexibility management policies that utilize the potential built into the systems.

International audience; Electric power distribution systems that link the bulk power grid (generation and transmission systems) to customers are the leading cause of power outages due to their vulnerability to extreme wind events, especially hurricanes. The strength of the wood poles that typically support the distribution lines also deteriorate over time. The vulnerability of the poles is expected to increase due to the potential impact of climate change on both hurricane hazard and wood decay rate. As such, an effective maintenance planning method is required for the vast number of poles supporting distribution lines. This paper presents a framework to optimize the maintenance of a network of wood utility poles. Corrective replacement due to failure caused by hurricanes and preventive replacement due to excessive decay are considered. The objective is to find the optimal inspection interval for the preventive replacement to minimize the long-term maintenance cost. To solve the optimization problem, the decay of the poles is modeled as a stationary gamma process. The impact of climate change on the rate of pole failure and replacement is also investigated. Two locations are considered as case studies: Miami, Florida, and New York City, New York. The period from 2010 to 2099 is considered for the study. The results of the case study show that the optimal inspection/replacement cycle determined using the developed framework results in lower total maintenance costs compared to current typical utility practice. Based on the inspection and replacement costs used in the study, the results show that adopting a periodic preventive maintenance policy decreases the failure rate of the poles but increases the total maintenance cost. However, only the cost of replacing the poles is considered here. Other considerations, such as indirect costs due to power outages and the impact of pole failure on system reliability, can render the adoption of a preventive replacement policy cost-effective. The results also show that climate change can increase the total maintenance cost. Based on current typical utility maintenance practice, climate change can increase the total maintenance cost by up to 8% in Miami and 6% in NYC, depending on the emission scenario considered.

Chloride-induced corrosion and load induced concrete cracking affect the serviceability and safety of reinforced concrete (RC) structures. Once these phenomena occur simultaneously, the prediction of RC structures&rsquo, lifetimes becomes a major challenge. The objective of this paper is to propose a methodology to evaluate the effect of loading and cracking on the mechanism of chloride ion penetration in concrete. The proposed methodology will be based on Bayesian networks. Bayesian networks are useful to update the lifetime assessment based on experimental data as well as to characterize the uncertainties of the input parameters of a chlorination model including a chloride diffusion acceleration factor. The proposed methodology is illustrated with experimental data coming from tests on RC beams subjected to static and cyclic loading before being in contact with a solution containing chloride ions. The characterized parameters are then used to evaluate the effect of these two loading conditions (static and cyclic) on the corrosion initiation time and the corrosion initiation probability. The results obtained indicate that the proposed methodology is capable of integrating loading and chlorination test data for the determination of the probabilistic parameters of a model in a comprehensive way.

Bio-colonisation affects the ageing of materials and the behaviour of offshore structures. Mooring systems and umbilicals belong to the family of slender bodies which are components sensitive to bio-colonisation because of a change of dynamic behaviour due to shape, roughness and mass modifications. However, this stochastic process in time and space is hard to predict. The purpose is then twofold: first, to provide a stochastic spatial model of the bio-colonisation on a mooring line, second, to show that in some defined environmental conditions, such as low wave height, low wind and current velocities, the monitoring of mooring lines tension can help to assess and reduce uncertainty on this model. Therefore, a comprehensive stochastic modelling based on mussels colonisation was carried out using on-site videotapes, experimental campaigns and expert knowledge. We studied the efficiency of a virtual sensing network using this model and a conditional entropy metric. It is first shown that the spatial model fits well with experimental data, and second that a denser medium accuracy sensor network is to be preferred to a single high accuracy fairlead sensor to reduce the uncertainty on the model parameters. It is then worth updating bio-colonisation on mooring lines during the life-time of a floating wind turbine.

Durability of reinforced concrete (RC) structures is affected by certain environmental conditions and operational actions which can reduce their lifetime significantly. Among these actions, this paper proposes a stochastic model that accounts for the combined effects of chloride-induced corrosion, climate change and cyclic loading. Separately, corrosion leads to cross-section reduction, climate change produces changes in temperature and humidity and fatigue induces nucleation and propagation of cracks in the rebars. When considered together, pitting corrosion nucleates cracks while environmental factors affect the kinematics of chloride ingress and corrosion propagation. The proposed approach is illustrated with the reliability analysis of a bridge girder subjected to cyclic loading under various environmental conditions. The overall results indicate that climate change effect induces lifetime reductions ranging between 1.4 and 2.3% if fatigue load is neglected. Under cyclic loading, total lifetime reduction increases up to 7%.

International audience; Structural reliability assessment is largely influenced by the spatial variability of material properties or defaults; however, there are still various challenges for their characterization and modeling. Structural Health Monitoring (SHM) could provide useful information in space and time for spatial variability characterization of material properties and mechanical solicitations; nevertheless, this challenge is arduous because of the large number of potential sensor positions of local disruptions/failures. This paper proposes a methodology to optimize the spatial distribution of embedded sensors used for spatial variability assessment of stationary random fields. The optimization criterion relies on the width of the confidence interval of statistics for the characteristics to identify. For sake of simplicity, the paper illustrates the method for one-dimensional problems. The proposed method is applied firstly to a numerical example were several hypothetical structural configurations that could be found in practice are studied. It is finally applied to two case studies (a reinforced concrete beam and a steel wharf) where water content and loss of steel thickness are respectively measured. The results show that the stationary property is useful to deduce the minimum quantity of sensors and their position for a given quality requirement. They also allow us to propose a criterion for defining if regular or non-regular spacing of sensors along the inspection zone is more appropriate depending on the component length and autocorrelation structure of the random field.

International audience; The mechanical and physical properties of wood structural elements and of wood structures are strongly affected by the combination of humidity, temperature variation and biological attack. The aim of this study is to develop a design model able to estimate timber elements decay function of the exploitation climatic conditions (temperature and humidity). The deterioration program may be applied on any type of wood element and is indicating the necessity of increasing the cross section dimensions if and when the specific humidity and temperature become of significant influence. The results of this study are of great importance as the behavior of a non-treated timber element can be surveyed when directly influenced by changes in climatic conditions (relative humidity and temperature).

International audience; Reliability assessment of existing timber structures subjected to deterioration processes is an important task to evaluate their serviceability and safety levels. Towards this aim, data collected after inspection campaigns are often used for updating structural reliability and planning future maintenance/inspection activities. Under natural conditions, timber decay involves a large number of uncertainties related to material properties and environmental exposure. These uncertainties are also affected by temporal and spatial variability of associated deterioration processes. In this context, the main objective of this study is to propose a Dynamic Bayesian Network approach for updating the structural reliability of deteriorating timber structures using inspection data. The proposed approach can account for the uncertainties in the decay process and the effect of spatial variability. It is also useful for reliability updating considering the uncertainties of inspection techniques. The proposed methodology is illustrated with the reliability updating of a timber beam subjected to decay deterioration. Results indicate that this approach is useful for evaluating and updating of structural reliability from spatially distributed inspection data. Reliability updating could also be carried out from partial observations at given areas, which is very useful for large-scale infrastructure.

International audience; Les ouvrages offshores en béton armé sont soumis à des phénomènes couplés de corrosion et de fissuration due aux chargements, qui affectent leurs durabilités. Pour comprendre les effets de couplage, plusieurs essais expérimentaux ont été réalisés puis implémentés. Le modèle numérique élaboré est fait à partir des données de l’étude d’une poutre en béton armé de dimension 300x120x1500 mm soumise à des chargements statiques et cycliques, puis exposée dans un environnement contenant des ions chlorures. Il permet de mettre en évidence les effets du chargement sur le mécanisme de pénétration des ions chlorure dans le béton et d’identifier, par la méthode des réseaux bayésiens, un facteur d’accélération de la diffusion des ions chlorure dû au chargement. Les résultats obtenus indiquent que l’approche utilisée est capable d’intégrer des données des essais de chloration et chargement pour la détermination des paramètres probabilistes d’un modèle.

International audience; This work presents the spatiotemporal evolution of the mechanical characteristics of the Ozigo wood beam (Dacryodes buettneri) subjected to nine years of creep in an unsheltered outdoor tropical climate. These beams were sawn into nine sections of 340 mm in length and subdivided into three portions in the direction of height (upper, middle and lower). From each portion, two flexural, two tensile and four compression specimens were extracted. The present study concerns the 108 compression test pieces with a cross-section of 20 x 20 mm 2 and a length of 120 mm. Longitudinal compression tests yielded the modulus of elasticity and failure stress. There is a decrease in stiffness of about 60% and 56% of the stress due to the combined effects of mechanical loading and environmental variations. This work highlights the thermo-visco-hygro-mechanical effects on a wooden structure exposed in an unsheltered outdoor tropical environment.; Ce travail présente l’évolution spatiotemporelle des caractéristiques mécaniques des poutre de bois d’Ozigo (Dacryodes buettneri) soumises à neuf ans de fluage en climat tropical extérieur non abrité. Ces poutres ont été sciées en neuf tronçons de 340 mm de longueur et subdivisées en trois portions dans le sens de la hauteur (haut, médian et bas). De chaque portion, on extrait deux éprouvettes de flexion, deux de traction et quatre de compression. La présente étude porte sur les 108 éprouvettes de compression de section 20 x 20 mm 2 pour 120 mm de long. Les essais de compression longitudinale ont permis d’obtenir le module d’élasticité et la contrainte de rupture. On observe une diminution de la rigidité de l’ordre de 60 % et 56 % de la contrainte due aux effets combinés du chargement mécanique et des variations environnementales. Ce travail met en lumière les effets thermo-visco-hygro-mécaniques sur une structure en bois exposée dans un environnement tropical extérieur non abrité.

International audience; This study demonstrates the possibility of measuring a local water content without prior calibration using a fiber optic sensor based on Fresnel reflection. The experimental approach was carried out on an epoxy structural adhesive. Three samples were instrumented with fiber optic sensors and immersed in distilled water. The reflected light intensity was analyzed using a Maxwell-Garnett effective medium model that considers spherical water inclusions in an epoxy matrix. The water contents measured in this way were validated by comparing them with the values given by an analytical resolution of the diffusion equation and a finite element simulation. In an industrial setting, this experimental approach could be used to monitor the aging of a polymeric material, an adhesive joint or a composite structure.; Cette étude démontre la possibilité de mesurer, sans étalonnage préalable, une teneur en eau locale à l’aide d’un capteur à fibre optique basé sur la réflexion de Fresnel. L’approche expérimentale a été réalisée sur un adhésif structural époxy. Trois échantillons ont été instrumentés de capteur à fibre optique et immergés dans de l’eau distillée. L’intensité lumineuse réfléchie a été analysée à l’aide d’un modèle de milieu effectif de type Maxwell-Garnett qui considère des inclusions sphériques d’eau dans une matrice époxy. Les teneurs en eau mesurées ont été validées par comparaison avec une solution analytique et avec une simulation par éléments finis. Dans un cadre industriel, cette approche expérimentale pourrait être utilisée pour surveiller le vieillissement d’un matériau polymère, d’un joint de colle ou d’une structure composite.

Problems of uncertainty quantification usually involve large number realiza-tions of a stationary spatial Gaussian random field over a regular grid points. This paper analyzes the convergence of the continuous spectral method for generating a stationary Gaussian random field. The continuous spectral method is the classical approach which discretizes the spectral representation integral to construct an approximation of the field within the Fast Fourier Transform algorithm. The method can be used as an alternative of circulant embedding approach when the discrete covariance matrix is not valid. We demonstrate that the method is computationally attractive when the spectral is a smooth function and decreases rapidly to zero at infinity. In such case, The spectral method is a very versatile approach for generating Gaussian stochastic fields. A simulation results are realized using pseudo-random data based on Monte-Carlo simulations to illustrate the theoretical bound of the method regarding the regularity of the random field and its spectral density.

International audience; Global offshore wind technology shows increasing progress evidenced in the recent reports of wind power capacity, expectations of market expansion and international research projects. Colombia is privileged with several types of natural resources (e.g. wind, sun, water) but there is not a clear legal context to regulate sustainable and safe exploitation of the offshore wind energy considered non-conventional. The development of offshore wind technology in Colombia could attend the energy demand when the hydroelectric system presents low electricity generation during dry hydrological conditions and El Niño-South Oscillations events. This paper analyses international actions that have motivated different countries to establish strategies to reduce CO2, and their advances and challenges in implementing offshore wind technology. The review of the administrative framework of renewable energy in Colombia proved the lack of information for implementing offshore wind

International audience; Relevant material and environmental parameters are required in modelling chloride ingress into concrete. They could be determined from experimental data (concrete cores taken during inspection) but in practice data availability is limited by time-consuming and expensive tests. Consequently, the main objective of this paper is to develop an approach based on Bayesian networks (BN) to improve the parameter identification when inspection data is limited. We aim at proposing appropriate inspection configurations that reduce inspection costs and identification errors for different exposure conditions and materials. It was found that it is possible to define an optimal number of inspection points in depth for allowed identification errors defined by decision makers. The optimal number of inspection points depends on both exposure and material properties. The random variables identified with the improved BN configurations are used to assess the probability of corrosion initiation. The results indicate that the improved BN configurations are useful to identify model parameters even from scarce inspection data.

International audience; Corrosion is one of the most significant threats for onshore pipelines that may lead to a Loss of Containment (LOC). A LOC poses significant consequences over the surrounding people and environment because of the hazardousness of the transporting fluids, so different efforts have been raised to predict pipe failures, which are commonly based on reliability assessments with limit state functions. These functions are gathered in serviceability, leakage, and ultimate conditions, out of which the last two approaches contemplate a LOC. This paper reviews recognized limit state functions for corroded pipelines, and it discusses their assumptions and applicability. Specifically, this paper focuses on burst limit pressures considering the relevance in the academic literature and Oil & Gas standards. Therefore, a thorough comparison is presented based on failure criteria, acceptable defect dimensions, failure probability, and error prediction based on experimental and numerical burst tests. The objective is to evaluate the level of conservatism of each simplified model depending on the material toughness and the corrosion rate. This review aims to support a reliability model selection in corroded pipelines for future intervention strategies.

International audience; Chloride ingress and carbonation are the main factors leading to corrosion initiation of reinforced concrete (RC) structures. Lifetime assessment and maintenance optimization of these deteriorating structures has been based for several practical applications on analytical predictive models. The literature review shows that there are numerous analytical models of chloride ingress and carbonation. It was also found that comprehensive lifetime assessment requires that the selected models be able to propagate uncertainties in a correct manner. Thus, this paper proposes a methodology for probabilistic sensitivity analysis of analytical models for chloride ingress and carbonation. Given that di↵erent parameter notations were found for each model, a homogenization of notations and generic forms are first proposed. The sensitivity analysis is based on the following indicators: elasticity coecient, Pearson coecient, bias of the mean and standard deviation of the response of the model. The results highlighted which parameters are influential for each model by considering three concrete types. Overall results indicated a higher e↵ect of the non-linearity of the models on the sensitivity indicators. It was found that the level of influence of each parameter depends also on the concrete type and the duration of the exposure to chlorides or carbon dioxide.

Vulnerability of seismically deficient bridges, coupled with their ageing and deterioration, pose significant threat to safety, integrity and functionality of the highway network that could result in significant risks to public safety, traffic disruption, and socio-economic impacts. Given the limited funds available for bridge retrofit, there is a need for an effective management strategy that will enable engineers to identify and prioritise the high-risk bridges for detailed seismic evaluation and retrofit. A practical risk-based preliminary seismic screening technique is proposed in this paper that enables to develop a ranking or prioritization scheme for seismically-deficient bridges. The complex interactions between seismic hazard, bridge vulnerability and consequences of failure are handled in a hierarchical manner. A Bayesian belief network based modelling technique is used to aggregate through the hierarchy and generate risk indices by accounting for chloride-induced corrosion deterioration mechanisms. The efficacy of the proposed method is illustrated on two existing bridges that are assumed to be located in high seismic zones and designed under different standards concerning their structural safety under seismic loads and durability performance.

International audience; The characterization of damages from output-only vibration measurements is an important issue for Structural Health Monitoring (SHM), in particular for bridges under ambient excitation. In the last years, a multitude of methods has been proposed for vibration-based damage detection, lo-calization and quantification. In this work, a benchmark application for such methods is proposed, namely a 1/200 scale model of the Saint-Nazaire Bridge, which is a cable-stayed bridge spanning the Loire River near the river's mouth. The region of interest, the central metallic structure, measures 720 meters. The aim of the instrumentation is to assess the capability of damage assessment methods to assess a cable failure. The model is instrumented with ten accelerometers and excited by white noise. A damage localization method is applied to test the proposed setup, namely the statistical damage locating vector approach (S-SDDLV). With this method, vibration measurements from the (healthy) reference and damaged states of the structure are confronted to a finite element of the reference state. Damage indicators are provided for the different structural elements that are easy to compute, without updating the model parameters, and taking into account the intrinsic uncertainty of noisy measurements.

International audience; Cracking initiation and propagation are frequently recognized as main causes leading to failure of timber structures. Since the kinematics of both processes is largely influenced by environmental conditions, a comprehensive reliability assessment of notched structures should take into account such environmental factors. The main purpose of this paper is to propose a methodology for reliability assessment and updating of notched timber components based on mechanical (A-integral formulation) and reliability (simulation and Bayesian networks) methods, and experimental data. The A-integral formulation is used to estimate energy release rates in modes I and II by taking into account thermal effects; but its numerical implementation is time-consuming for uncertainty propagation. In order to deal with this problem, Bayesian networks were used for reliability assessment and updating. The experimental data used for updating purposes were obtained from measurements of deflection, temperature and relative humidity on a notched beam (Douglas Fir specie) exposed to outdoor environment and constant loading. The whole proposed methodology was illustrated with the reliability assessment and updating of the studied notched beam. The results indicated that the proposed approach is able to integrate measurements of temperature and deflection for reliability updating.

International audience; An inflatable beam is an airtight structure made of a soft technical fabric and subjected to an internal pressure which gives it a final cylindrical shape, a pre-stress in the membrane and a bearing capacity. Against all appearances, it is not a standard beam and it requires a specific formulation in order to take account of the internal pressure which plays a key role in its mechanical response. This work deals with inflatable beams made of orthotropic materials. The first part of the paper is concerned with the inflation of the membrane tube, an important stage which is often neglected so far in the literature. As preliminaries of the bending problem studied in the next part of the paper, the constitutive law related to the inflated state of the tube – not the natural state – is investigated. It will be shown that the consti-tutive law related to the inflated pre-stressed state is not the same as the constitutive law related to the natural state. Expressions of the material coefficients involved in the former constitutive law will be established from the material coefficients defined on the natural reference configuration which are the only ones supposed to be known. The second part of the paper deals with the bending of the inflatable beam. The Tim-oshenko beam kinematics will be chosen because of the significant shear effect in the tube wall and the problem will be formulated in finite deformations in order to accounts for all the nonlinear effects, in particular the action due to the internal pressure which is a follower load. The nonlinear system of equations obtained will then be linearized around the pre-stressed configuration and will result in a more tractable linear system. The proposed formulation allows a comprehensive study of the influence of the internal pressure on the geometry and material properties of orthotropic inflatable beams The analytical results will be compared with numerical results obtained from a nonlinear membrane finite element code.

International audience; Concrete is the predominant construction material for buildings, bridges, wharves, and other infrastructure worldwide. A potentially important factor for asset management is the possible influence of climate change. This may alter the environment to which infrastructure is exposed, and in turn may alter the factors known to affect the corrosion of reinforcing steel, including atmospheric CO2 concentration, temperature, humidity, ocean acidification, airborne pollutants, etc. This chapter poses the problem of adaptation of deteriorating RC structures. It describes a framework for evaluating the cost-effectiveness of adaptation measures that accounts for deterioration models, probabilistic methods and cost-benefit analysis. The methodology is illustrated with an example focusing on cost-effective adaptation of existing RC structures placed in the coastal French cities of Saint-Nazaire and Marseille.

International audience; Nowadays, environment effects, and in particular the reduction of greenhouse effect, are one of the most important issues that are of great concern to the research community. As per the Kyoto protocol and the COP 21 meeting, the use of wood in civil engineering structures reminds one solution for the regulation of these effects by minimizing both CO 2 emission and the use of grey energy. Since the wood mechanical behaviour is quite complex due to its anisotropic constitution, the coalescence of various defects (nodes, orientation of annual rings, …) during its service life, the increasing use of wood as structural material in civil engineering is a major challenge, and needs to increase scientific efforts in understanding the mechanical behaviour of timber structures. In order to bring some responses to these scientific problems, the JCJC 2013 CLIMBOIS research project (Moutou Pitti et al. 2014) is dealing with the effects of climatic and mechanical variations on the durability of notched timber structures. Material cracking is one of the most important factors involved in the collapse of structures. However, if the crack initiation is detected earlier, and the monitoring of the crack propagation within the materials is under control, the structural integrity of buildings can be easily evaluated by sending alerts. Within the framework of this research project, the study carried out herein is devoted to both an identification of failure

International audience; The investigation of tropical behaviour woods in their environment is a real challenge for the prediction of the structural responses of tropical timber structures subjected to thermo-hygro-mechanical loadings. The present study is focused on the experimental characterization and modelling of the spatial variability of the physical-mechanical parameters (density, modulus of elasticity, compression and flexion) of a solid wood beam subjected to outdoor conditions in the south of Gabon into equatorial Region. Figure 1: (a) Beams in sheltered outside climate; (b) specimens, (c) cross-sections, (d) Spatial specimen modelling; (e) Experimental device modelling.

International audience; Non-destructive monitoring of crack growth within material becomes an essential tool to better understand cracking mechanisms of materials, and therefore to reduce failure risks. This paper presents results from laboratory static tests that were conducted to investigate the monitoring of crack tip growth within wood material. Double Cantilever Beam specimens with variable inertia were tested in opening mode configuration. Acoustic emission (AE) technique was used to monitor the acoustic activity within wood material. In a first step, the reliability of the crack tip monitoring is evaluated in terms of Probability of Detection (PoD). Results show that for all specimens the PoD is larger than 70% for a detection threshold of 1 mm. In a second step, a K-means++ algorithm was used to perform a cluster analysis of AE data, and to allow the AE events that were generated by the crack tip growth to be identified. Evolutions of both strain energy and AE energy are compared, and the experimental results show that the first AE events appear when the wood material reaches its limit to store strain energy, so at the vicinity of the end of its linear elastic behaviour.Highlights DCB wood specimens with variable inertia were tested in opening mode configuration. Unsupervised classification of AE events to identify three failure mechanisms. Probability of Detection to evaluate the reliability of the crack tip monitoring. Probability of Detection is larger than 70% for a detection threshold of 1 mm.

International audience

International audience; Vulnérabilité et coûts des mesures d'adaptation des logements exposés au risque de submersion marine axel.creach@univ-nantes.fr emilio.bastidas@univ-nantes.fr Références : Creach A., Pardo S., Guillotreau P. et Mercier D. (2015), The use of a micro-scale index to identify potential death risk areas due to coastal flood surges: lessons from Storm

International audience; Most of the approaches for diagnosis or prognosis of deteriorated reinforced concrete(RC) structures are based on two stages: acquiring data (concrete properties, quantitative degradation information), and then predicting the evolution of degradation by using appropriate models. Spatial variability of both properties and degradation processescannot be neglected in the lifecycle assessment and implies that (i) data should be acquired for a representative part of the concrete surface and (ii)models should be capable of dealing with this variability.However, the assessment and modeling of spatial variability is not a straightforward task particularly when uncertainties affect the measurementsorwhen the number of measurements is limited.The present paper aims at studying the capability of analytical carbonation models to deal with the spatial variability of model inputs in terms of spatial correlation of model outputs.Analytical models are considered herein because they provide practical and usual tools in engineering. This paper focuses on the case of a RC wallexposed to atmospheric carbonation where concrete properties and carbonation depths were measured by destructive techniques at several points over a linear portion of a wall within the framework of the French ANR EVADEOS project.Uncertainties due to experimental devices and procedures are estimated and propagated throughout random field models to account for spatial variability of spatial observations. Correspondence indexes are proposed to rank carbonation models with respect to their ability of reflecting the observed correlation profiles of carbonation depth. It was found that for the available database the proposed correspondence index that incorporates uncertainties was useful to assess the capabilities of models to deal with the spatial variability.

International audience; This paper presents a digital image correlation method able to detect and measure a contour or silhouette in a digital image, with a sub-pixel precision. A virtual image that describes a simple contour or silhouette roughly similar to the physical object to detect is created. The matching with the physical image of the object is then performed based on digital image correlation. We look for the displacement field which transforms the physical image which is the closest to the virtual one. In order to keep a problem of finite dimension, this field is decomposed on a B-spline basis. The algorithm is close to the digital image correlation method; an efficient implementation is proposed that makes use of levelsets. The full method is tested over both synthesized and real images, one of a star shaped toy and one on an ill-defined image of a high temperature metallic specimen on which no other boundary measurement was possible. The influence of the arbitrary choice of the virtual image contour or silhouette arbitrary parameters is discussed with respect to the precision of the method. This one is shown to be sub-pixel in any case.

International audience; A probabilistic analysis of the face stability of a pressurized tunnel is undertaken in this article. First, two existing velocity fields based on the limit analysis theory are briefly described. They allow one to compute the values of the critical pressures of collapse and blowout of a pressurized tunnel face in cases of both frictional and nonfrictional soils. These models, which have the great advantage of a low computational cost, are validated by comparison with a computationally expensive numerical model. Then, an efficient probabilistic method called collocation-based stochastic response surface methodology (CSRSM) is applied on these velocity fields to perform the uncertainty propagation. This method makes it possible to compute the probability of failure of the tunnel face against both collapse and blowout. In the case of a frictional soil, it appears that the blowout of the face is extremely unlikely and that the collapse is the only probable failure mode. On the contrary, in a purely cohesive soil, it appears that both failure modes are likely to appear and should be considered in the analysis. Finally, this paper presents a discussion concerning the application of the proposed probabilistic method for an economic and safe design of a pressurized shield.

International audience; This paper addresses the topic of long-term characterisation and probabilistic modelling of chloride ingress into reinforced concrete (RC) structures. Since the corrosion initiation stage may cover various decades, normal tests which simulate chloride penetration into concrete in laboratory conditions as the same as natural conditions, will require significant experimental times. Hence, long-term lifetime assessment of RC structures under chloride attack remains still a challenge. In practice this problem is solved through the use of accelerated tests which speed up the chloride ingress rate and provide valuable mid-and long-term information on the chloride penetration process. Nevertheless, this information cannot be directly used for parameter statistical characterisation if the equivalent times required in natural conditions to reach the same chloride concentrations in the accelerated tests are unknown. Consequently, this study proposes a novel iterative approach based on Bayesian network updating to estimate chloride ingress model parameters from the data obtained under accelerated laboratory conditions. The Bayesian Network structure and iterative approach are first tested with numerical evidences. Thereafter, the complete proposed methodology is verified with results from real experimental measurements. The results indicate that combining data from normal and accelerated tests significantly reduces the statistical characterisation error of model parameters.

International audience; Flexible piezoelectric device has been realized by depositing lead zirconate titanate (PZT) thin films by Chemical Solution Deposition (CSD) onto very thin aluminium foil (16 µm) and using polyethylene terephthalate (PET) laminated film (150 µm) as encapsulation. A ruthenium dioxide layer has been used in order to enhance the quality of the PZT/Al interface, improving the dielectric, ferroelectric and piezoelectric properties of the PZT film. The obtained piezoelectric generators have been subjected to large bending motions at low frequencies ranging from 0.1 to 8 Hz and the experimental values of the output voltage, output current and harvested power have been compared to theoretical values (derived from the electrokinetic model of the piezoelectric material) with a very good agreement. Due to the increase of the permittivity of the PZT film by the use of RuO2 interlayer, moderate decrease of the harvested power at the optimal load resistance is found (from 185 nW to 143 nW at 4.4 Hz), despite the enhancement of the piezoelectric properties. This type of very flexible film able to withstand small radius of curvature (1 cm) may yield promising avenue in the field of low frequency mechanical energy harvesting.

International audience; Chloride penetration is among the main causes of corrosion initiation in reinforced concrete (RC) structures producing premature degradations. Weather and exposure conditions directly affect chloride ingress mechanisms and therefore the operational service life and safety of RC structures. Consequently, comprehensive chloride ingress models are useful tools to estimate corrosion initiation risks and minimize maintenance costs for RC structures placed under chloride-contaminated environments. This paper first presents a coupled thermo-hydro-chemical model for predicting chloride penetration into concrete that accounts for realistic weather conditions. This complete numerical model takes into account multiple factors affecting chloride ingress such as diffusion, convection, chloride binding, ionic interaction, and concrete aging. Since the complete modelcould be computationally expensive for long-term assessment, this study also proposes model simplifications in order to reduce the computational cost. Long-term chloride assessments of complete and reduced models are compared for three locations in France (Brest, Strasbourg and Nice) characterized by different weather and exposure conditions (tidal zone, de-icing salts and salt spray). The comparative study indicates that the reduced model is computationally efficient and accurate for long-term chloride ingress modeling in comparison to the complete one. Given that long-term assessment requires larger climate databases, this research also studies how climate models may affect chloride ingress assessment. The results indicate that the selection of climate models as well as the considered training periods introduce significant errors for mid-and long-term chloride ingress assessment.

National audience

This paper reports a simple, quick and cheap method for transferring Pb(Zr,Ti)O 3 (PZT) thin film onto polymer substrate. To achieve a low-cost transfer process, piezoelectric thin film are deposited onto a sacrificial commercial aluminium substrate to target polymer substrate by a wet etching technique. This novel flexible piezoelectric structure was characterized to evaluate its crystal structure and its morphologic properties. This new process should allow to develop novel applications for low frequency vibrations energy harvesting.

International audience

International audience; The quality of a statistical estimation process is directly linked to the richness of the available database. In Civil Engineering, it is rare to consider that the structures forming a database are homogeneous. We are always in the compromise between a sufficient number of observations and the homogeneity of the database. In this paper, we are interested in the relationship between the specific characterization of the behaviour of an individual from a given population and the qualification of a database according to its level of heterogeneity. To this aim, we propose to analyse the performance of the estimation process in terms of statistical relevance to degradation model using simulated databases with different levels of heterogeneity. This study aims to draw the first points for methodological qualification of a heterogeneity in database decision support in a context of risk management and maintenance. The studied degradation model is based on a bi-variate, state-dependant stochastic processes with a gamma distribution.; La qualité d’un processus d’estimation statistique est directement liée à la richesse de l’échantillon disponible. Dans un contexte de Génie Civil, il est rare de pouvoir considérer que les structures formant cet échantillon soient homogènes. Nous sommes donc toujours dans le compromis entre un nombre suffisant d’observations et l’homogénéité de ce même échantillon. Nous proposons dans cette communication de nous intéresser à la relation entre la caractérisation spécifique du comportement d’un individu parmi une population donnée et la qualification d’une base de données en fonction de son niveau d’hétérogénéité. Pour cela, nous proposons d’analyser les performances en termes d’adéquation statistique au modèle de dégradation sur la base de données simulées présentant des niveaux d’hétérogénéité différents. Cette étude permet de dessiner les premiers points pour une méthodologie de qualification d’une base de données en terme d’hétérogénéité orientée aide à la décision dans un contexte de gestion des risques et de maintenance. Le modèle de dégradation étudiée est basé sur des processus stochastiques, dépendant de l'état, non stationnaire, et ayant une distribution gamma.

International audience; The quality of a statistical estimation process is directly linked to the richness of the available database. In Civil Engineering, it is rare to consider that the structures forming a database are homogeneous. We are always in the compromise between a sufficient number of observations and the homogeneity of the database. In this paper, we are interested in the relationship between the specific characterization of the behaviour of an individual from a given population and the qualification of a database according to its level of heterogeneity. To this aim, we propose to analyse the performance of the estimation process in terms of statistical relevance to degradation model using simulated databases with different levels of heterogeneity. This study aims to draw the first points for methodological qualification of a heterogeneity in database decision support in a context of risk management and maintenance. The studied degradation model is based on a bi-variate, state-dependant stochastic processes with a gamma distribution.; La qualité d’un processus d’estimation statistique est directement liée à la richesse de l’échantillon disponible. Dans un contexte de Génie Civil, il est rare de pouvoir considérer que les structures formant cet échantillon soient homogènes. Nous sommes donc toujours dans le compromis entre un nombre suffisant d’observations et l’homogénéité de ce même échantillon. Nous proposons dans cette communication de nous intéresser à la relation entre la caractérisation spécifique du comportement d’un individu parmi une population donnée et la qualification d’une base de données en fonction de son niveau d’hétérogénéité. Pour cela, nous proposons d’analyser les performances en termes d’adéquation statistique au modèle de dégradation sur la base de données simulées présentant des niveaux d’hétérogénéité différents. Cette étude permet de dessiner les premiers points pour une méthodologie de qualification d’une base de données en terme d’hétérogénéité orientée aide à la décision dans un contexte de gestion des risques et de maintenance. Le modèle de dégradation étudiée est basé sur des processus stochastiques, dépendant de l'état, non stationnaire, et ayant une distribution gamma.

International audience; Multiple constraints imposed by economic, social and environmental considerations lead maintenance planning optimization to a major challenge for designers, owners and users of infrastructure. This study focuses on the management of reinforced concrete (RC) structures placed in chloride-contaminated 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 comprehensive maintenance strategy. This paper presents a new methodology for improving the performance of maintenance strategies for corroding RC structures. The proposed approach is based on preventive maintenance and combines: a numerical 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 in the model. The aforementioned points are illustrated with a numerical example. In general, the overall results indicate that the proposed methodology can be useful to improve the costs of a given maintenance strategy by ensuring appropriate levels of serviceability and safety.

International audience; In this paper, a probabilistic analysis is presented to compute the probability density function (PDF) of the ultimate bearing capacity of a shallow strip footing resting on a rock mass. The rock is assumed to follow the modified Hoek-Brown failure criterion. Vertical and inclined loading cases are considered in the analysis. In this study, the deterministic models are based on the kinematic approach of the limit analysis theory. The polynomial chaos expansion (PCE) methodology is used for the probabilistic analysis. Four parameters related to the modified Hoek-Brown failure criterion are considered as random variables. These are the geological strength index (GSI), the uniaxial compressive strength of the intact rock (sigma(c)), the intact rock material constant (m(i)) and the disturbance coefficient (D). The results of the vertical load case have shown that (i) the variability of the ultimate bearing capacity increases with the increase in the coefficients of variation of the random variables; GSI and sigma(c) being of greater effect, (ii) the non-normality of the input variables has a significant effect on the shape of the PDF of the ultimate bearing capacity, (iii) a negative correlation between GSI and sigma(c) leads to less spread out PDF, (iv) the probabilistic footing breadth based on a reliability-based design (RBD) may be greater or smaller than the deterministic breadth depending on the values of the input statistical parameters. Finally, it was shown in the inclined load case that the variability of the ultimate bearing capacity decreases with the increase of the footing load inclination.

International audience; In the past years, an increasing number of structures have been equipped with permanent monitoring systems, able to record the structural response in terms of displacements and strains over very long periods of time, and theoretically, for the entire life of the structure (Structural Health Monitoring). Despite the high number of applications, to date, very few studies have been presented aimed at interpreting the data, in particular, when the spatial and behavioral complexity of the structure under investigation requires a non-model-based approach. This article shows that the interpretation of data from a long-term static monitoring can be very helpful for the comprehension of the structural behavior under complex interaction structure-environment. The discussion aims at underlining that a scheduled and unique procedure is very hard to define depending on the great variety of structures and applications and on the right identification of the parameters able to explain structural degradation evolutions or sudden changes. In these cases, a multi-step algorithm with different signal processing techniques applied in cascade seems to be the only reliable approach. The proposed procedure will be carried out using available data from the long-term monitoring of a quay wall in the Port of Genoa, in Italy, but it can be generalized to several structures under cyclic environmental loading (tides, temperature, etc.). The characterization of the structural behavior under temperature variations will be used here to define the representative features of the quay. Once defined, these parameters will provide a means for detecting and localizing the insurgence of damage or material degradation from the measurements.

International audience; Reinforced concrete (RC) structures placed in chloride-contaminated environments are subjected to deterioration processes that affect their performance, serviceability and safety. Chloride ingress leads to corrosion initiation and its interaction with service loading could reduce its operational life. Chloride ingress and corrosion propagation are highly influenced by weather conditions in the surrounding environment including climate change. Therefore, both structural design and maintenance should be adapted to these new environmental conditions. This study focuses on the assessment of the costs and benefits of climate adaptation strategies for existing RC structures subjected to chloride ingress and climate change. We studied RC structures built at different periods under different construction standards in France. The cost-effectiveness of adaptation measures was measured in terms of the Benefit-to-Cost Ratio (BCR) and the probability that BCR exceeds unity –i.e., Pr(BCR>1). The results of the paper could provide practical advice to policy makers to improve the management of existing RC structures under a changing climate by discussing the influence of the following factors on the mean BCR and Pr(BCR>1): specific exposure conditions, climate change scenarios, risk reduction due to the implementation of adaptation strategies, type of structural component, years of construction and adaptation, discount rates and damage costs.

International audience; The 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.

National audience

International audience; Characterization of randomness and spatial variability of material properties, loading or deterioration processes of structures, from inspection, is a very challenging task that concentrates the improvement of Non Destructive Testing (NDT) tools on more efficient and higher structural coverage. In case of characterization of random loading or material properties, this challenge is arduous because of the limited number of measures and the quasi-infinite potential positions of local failures. This paper presents a two stages procedure for the stochastic characterization of random fields from NDT measurements. According to the stationarity property, the optimal quantity of NDT measurements and their position can be assessed once a quality requirement is included. The proposed procedure allows: (i) to quantify the properties of the ergodic stationary field, and (ii) to assess the second order parameters of the studied random variables. The paper ends illustrating the methodology with an application that considers the inspection of a concrete beam with a capacitive technique. The results indicate that the proposed methodology is useful to identify the parameters of a random field by reducing the number of NDT measures under given quality requirements.

The reassessment of existing structures leads to analyse the impact of local defects on the structural behaviour. This paper proposes a cracked beam finite element with a view to introducing the effect of large through-cracks in the structural analysis for framed structures like jacket offshore platforms. The model parameters are identified for several joint typologies using 3D finite element results. Copyright © 2007 John Wiley & Sons, Ltd.

International audience; Concrete biodeterioration in sewers and structures subjected to environments rich in hydrogen sulfide has been related to the activity of sulfur oxidizing bacteria (SOB). In previous studies, the effect of the activity of SOB on concrete structures has been linked mainly to weight loss. In our work we have investigated, in addition to the weight loss, the variations in porosity and compressive strength. The main objective of this paper is to explore, under controlled conditions, the effect of biodegradation of non-submerged samples, on both the physical properties and the mechanical performance. Towards this aim, cement mortar samples inoculated with pure cultures of Acidithiobacillus thiooxidans, Halothiobacillus neapolitanus, and a consortium containing both strains, were exposed to an H2S-rich environment. Changes in physical properties, including weight and porosity, and compressive strength were measured over 300 days. The results showed that the greatest reduction of weight and compressive strength was observed in samples inoculated with the consortium (7 and 52 %, respectively); while the largest variation in porosity was observed in samples inoculated with A. thiooxidans (27 %). These results were used to obtain relationships between the amount of sulfur available over time with specific physical and mechanical properties; i.e., compressive strength, porosity, weight loss, and physical appearance.

The mechanical and physical properties of timber structures could be affected by a combination of loading, moisture content, temperature, biological activity, etc. This paper focuses on the optimal design of new timber structures subjected to fungal decay. Among the optimization methods available in the literature, this study considers a Time-Dependent Reliability Based-Design Optimization approach. This method aims at ensuring a target reliability level during the operational life by considering deterioration and the uncertainties related inherent to materials properties, models and climate. This approach is applied to design optimization of a timber truss subjected to an aggressive (very humid) French climate. The performance of the optimized solution is compared, in terms of safety, with solutions estimated from Deterministic Design Optimization and the classical Reliability-Based Design Optimization approaches. The overall results indicate that the optimized solution obtained by the Time-Dependent Reliability Based-Design Optimization approach ensures the target reliability level during the whole structural lifetime.

In this work, the acoustic emission is used as a measurement technique to detect and locate the progress of the crack tip in a wooden specimen subjected to thermo-hygro-mechanical stresses. Under these stresses, the material response results in the release of energy in the form of transient elastic waves that are recorded by acoustic emission sensors. The post-processing of these acoustic signals is used to detect the position of the crack. There are many parameters that can affect the accuracy of acoustic emission such as noise signals, geometry, wood specie, etc. Consequently, this study combines repetitive tests and probabilistic approaches to characterize uncertainties and improve the acoustic emission protocol. In the experimental program, breaking of graphite mines at various known positions simulated acoustic sources. The differences between the real and detected positions are used to calibrate the tests and to improve the configuration of the sensors., Academic Journal of Civil Engineering, Vol 33 No 2 (2015): Special Issue - ICBBM 2015

The 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., Academic Journal of Civil Engineering, Vol 33 No 2 (2015): Special Issue - ICBBM 2015