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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; 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.

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; 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; 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.

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; 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; 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; 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.

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; 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; 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.

Many 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 range of protocols, techniques and materials for repair and there is not much information about their durability performance. This paper proposes a methodology for evaluating, comparing and/or improving the 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), carbon dioxide 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 significantly reduce environmental impact.

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 initiation and its interaction with service loading could reduce its operational life. Experimental evidence indicates that chloride ingress is highly influenced by weather conditions in the surrounding environment and therefore by climate change. Consequently, both structural design and maintenance should be adapted to these new environmental conditions. This work focuses on the assessment of the costs and benefits of two climate adaptation strategies for new RC structures placed in chloride-contaminated environments under various climate change scenarios. Their cost-effectiveness is measured in terms of the Benefit-to-Cost Ratio (BCR) and the probability that BCR exceeds unity –i.e., Pr(BCR>1). It was found that increasing concrete strength grade is more cost-effective than increasing design cover. The results also indicate that the cost-effectiveness of a given adaptation strategy depends mainly on the type of structural component, exposure conditions and climate change scenarios.

International audience; Probabilistic modelling of deterioration processes is an important task to plan and quantify maintenance operations of structures. Relevant material and environmental model parameters could be determined from inspection data; but in practice the number of measures required for uncertainty quantification is conditioned by time-consuming and expensive tests. The main objective of this paper is to propose a method based on Bayesian networks for improving the identification of uncertainties related to material and environmental parameters of deterioration models when there is limited available information. The outputs of the study are inspection configurations (in space and time) that could provide an optimal balance between accuracy and cost. The proposed methodology was applied to the identification of random variables for a chloride ingress model. It was found that there is an optimal discretisation for identifying each model parameter and that the combination of these configurations minimises identification errors. An illustration to the assessment of the probability of corrosion initiation showed that the approach is useful even if inspection data is limited.

International audience; A probabilistic analysis of vertically and obliquely loaded strip footings resting on a spatially varying soil is presented. The system responses are the footing vertical and horizontal displacements. The deterministic computation of these system responses is based on numerical simulations using the software FLAC3D. Both cases of isotropic and anisotropic random fields are considered for the soil elastic properties. The uncertainty propagation methodology employed makes use of a nonintrusive approach to build up analytical equations for the two system responses. Thus, a Monte Carlo simulation approach is applied directly on these analytical equations (not on the original deterministic model), which significantly reduces the computation time. In the case of the footing vertical load, a global sensitivity analysis has shown that the soil Young's modulus E mostly contributes to the variability of the footing vertical displacement, the Poisson ratio being of negligible weight. The decrease in the autocorrelation distances of E has led to a smaller variability of the footing displacement. On the other hand, the increase in the coefficient of variation of E was found to increase both the probabilistic mean and the variability of the footing displacement. Finally, in the inclined loading case, the results of the probability of failure against exceedance of a vertical and/or a horizontal footing displacement are presented and discussed.

International audience; Chloride ingress into concrete is one of the major causes leading to the degradation of reinforced concrete structures. Its modelling is an important task to plan and quantify maintenance operations of structures. Relevant material and environmental parameters for modelling could be determined from inspection data that is very limited due to time-consuming and expensive tests. The main objective of this paper is to develop a method based on Bayesian updating for selecting appropriate inspection configuration that can provide an optimal balance between accuracy and cost. The results indicate that Bayesian approach could be a useful tool to identify model parameters even from insufficient inspection data.

International audience; Chloride ingress and carbonation cause corrosion of reinforced concrete (RC) structures affecting its operational life. Experimental evidence indicates that these deterioration processes are highly influenced by CO2 emissions and climatic conditions in the surrounding environment - i.e., temperature, humidity, etc. Since studies on global warming announce changes in climate, the impact of changing climate on RC durability should also be considered. This paper links RC deterioration mechanisms to CO2 emissions and global warming. Based on various studies on climate change, models for estimating the effect of CO2 emissions and temperature/humidity changes due to global warming are described. Furthermore, various scenarios of global warming that can be used to assess the effect of climate change in structural reliability are proposed. The proposed approach is then illustrated with a numerical example that calculates the probability of failure of a RC bridge beam for future climate scenarios. The paper then outlines some adaptation strategies, particularly focusing on the needs for risk-based selection of optimal adaptation measures.

International audience; Welded joints are commonly used for various structures such as civil engineering infrastructures or marine and submarine structures. It is well known that the geometry of the joints has an important influence on the stress concentration factor and thus on fatigue lifetime. Non-Destructive controls during welding work allow to keep parameters inside bounds and to satisfy quality requirements. However, the effect of the geometry characteristics within these bounds on the structural lifetime needs for a statistical analysis and a probabilistic modelling on the one hand and for a specific computational method on the other hand. When considering the first point, only few works have been carried out on the statistical analysis of the geometrical parameters of a welded joint. The measurement of the different parameters of this geometry is a long and scrupulous work. Recently, some laser process allows obtaining a significant quantity of trajectories along a welded joint for these geometrical parameters. This paper aims at analysing these trajectories for reliability purpose. This laser process allowed us to measure the width of the weld, the angle at the junction between weld and welded component and the radius at the weld toe. The study was completely performed for the two first but it was shown that the assessment of the radius remains challenging.

International audience; Tunneling-induced ground movements are investigated in this paper using both deterministic and probabilistic analyses. The deterministic model is based on three-dimensional (3D) numerical simulations using the commercial code FLAC(3D). This model attempts to reproduce some major phenomena during a typical slurry-shield tunnel excavation (ground movements due to the applied face pressure, the overcutting, the shield conicity, the annular void behind the shield, and the grout injection in this void). Moreover, the model provides useful information about the nature and magnitude of the soil movements at the ground surface. A probabilistic study is then undertaken in order to evaluate the impact of the variability of several input variables on the ground movements. An efficient probabilistic method called CSRSM is used to assess this uncertainty propagation. In a last section, the output variables of the model are linked to failure criteria. This allows one to determine probabilities of failure, depending on the probabilistic properties of the input variables and on the admissible threshold of each criterion.

International audience; The computation of the failure probability of geotechnical structures considering the soil spatial variability is generally performed using Monte Carlo Simulation (MCS) methodology. This method is very time-consuming especially when computing a small failure probability. As an alternative, Subset Simulation (SS) approach was proposed by Au and Beck [3] to efficiently calculate the small failure probability. In the present paper, a more efficient approach called “improved Subset Simulation (iSS)” approach is employed. In this method, the first step of the SS approach is replaced by a conditional simulation in which the samples are generated outside a hypersphere of a given radius. The efficiency of the iSS approach is illustrated here through the probabilistic analysis at the serviceability limit state (SLS) of two neighboring strip footings resting on a soil with 2D spatially varying Young’s modulus. The system response is the differential settlement between the two footings. The probabilistic results have shown that the probability Pe of exceeding a tolerable differential settlement computed by the iSS approach is very close to that calculated by the MCS methodology applied on the original deterministic model. The results have also shown that the use of the iSS approach has reduced the number of calls of the deterministic model by about 50% with respect to the SS approach.

International audience; For several decades, many structures have been monitored during maintenance or during their service lives to analyse long-term behaviour. A large number of sensors, properly distributed in the structure, are necessary, especially if the structure is complex and includes significant spatial variability. When probabilistic modelling is applied, because of intrinsic uncertainties in the model as well as uncertain physical parameters, monitoring measurements can be used to identify the parameters of the structural model. This paper presents a monitoring example of a pile-supported wharf in which tie rods are instrumented and the geotechnical characteristics of the soil embankment are identified. The modelling is performed using a meta-model fitted with a numerical database obtained from direct simulations with a finite element model implemented with Plaxis. A full quadratic response surface model (RSM) is the most efficient approximation to fit the original finite element model. The identified soil parameters enable the model to describe the variability of the measured loading in the tie rods.

International audience; The aim of this article is the management optimisation (inspection, maintenance and rehabilitation (IM&R)) of a group of structures. It is supposed that the optimisation is constrained by limited available budget at the beginning of each time period during the entire time horizon thus creating an economical dependence between the decisions related to each of the structures. A Lagrangian relaxation technique is used for the extension of existing dynamic programming methods from single structure to multi-structures level. The methodology is illustrated by using a Generalised Partially Observable Markov Decision Process having a decision tree composed of a sequence of two decisions at the beginning of each time period, namely an inspection decision followed by a maintenance action decision. A numerical example concerning the optimisation of IM&R of 16 different bridges is presented.

International audience; The aim of this paper is to investigate the ability to measure simultaneously the axial and radial strain with a single optical fiber sensor. The discussion begins with the analytical study of a cylinder subjected to pure tensile strain and thermal load. We emphasize the necessity of measuring the radial strain in order to determine the axial strain of an embedded sensor with accuracy. Then, we describe a few sensors able to measure axial and radial strains and study their efficiency. The conclusion is that the best structure is made of the juxtaposition of a short and a long period grating.

International audience; This paper presents an extension to a partially observable Markov decision process so that its solution can take into account, at the beginning of the planning, the possible availability of free information in future time periods. It is assumed that such information has a Bayesian network structure. The proposed approach requires a smaller computational effort than the classical approaches used to solve dynamic Bayesian networks. Furthermore, it allows the user to (1)take advantage of prior probability distributions of relevant random variables that do not necessarily have a direct causal relationship with the state of the system; and (2)rationally take into account the effects of accidental or rare events (such as seismic activities) that may occur during future time periods of the planning horizon. The methodology is illustrated through an example problem that concerns the optimization of inspection, maintenance, and rehabilitation strategies of road pavement over a 14-year planning horizon.

International audience; In this paper, an analytical solution is proposed for a pressurized cylindrical tube made of an orthotropic membrane, with the orthotropy directions oriented at an arbitrary angle, not necessarily parallel to the tube axis. The formulation is made in the framework of finite deformations and results in a system of three non-linear equations, giving the final radius, length and rotation of the cross-sections of the tube, in the deformed configuration. The set of equations is solved for balanced and unbalanced materials, with various internal pressures and orientations of the membrane. The numerical results obtained are shown to agree very well with those of an independent finite element code.

International audience; Inflatable tubes must be pressurized before they are able to resist to external loadings. While there are many studies dedicated to the behavior of inflated tubes under bending or twisting, few results are available on the inflating stage when the beam is only submitted to the internal pressure. In this paper, an exact solution is proposed for a cylindrical tube made of an orthotropic membrane, with the orthotropy axes parallel to the circumferential and longitudinal directions of the cylinder, and undergoing finite deformations under internal pressure. The solution of the problem amounts to solving a cubic equation and analytical relations are given for the inflated geometry as well as the resultant stresses in the membrane. Numerical results are shown to compare very well with those obtained from a finite element code.

Preventive maintenance allows us to ensure an acceptable level of reliability during the structural lifecycle. A conditional maintenance policy is based on periodic inspections of degradation, which eventually trigger alarms related to repairs and replacements. In practice, however, quantitative knowledge of the state of degradation and operation conditions presents many uncertainties, which leads to a difficult decision-making process. Therefore, reliability-based maintenance becomes mandatory for decision-making.

International audience; Owners of civil infrastructure base their maintenance decision schemes mainlyon both structural integrity assessment and consequence analysis. Some inputs come frominformation collected by inspections with non-destructive or destructive tools.Uncertainties and errors of measurement can lead to bad decisions but are rarelyintegrated into the decision process. Currently, Risk Based Inspection (RBI) provides thebasic concepts for optimizing the maintenance plans of existing structures while insuringsatisfactory safety and availability of the structure during its service life. It lies both onreliability computations and probabilistic modeling of inspection results. This last pointleads to introduce the Probability of Detection, and the Probability of False Alarms thatare usually considered as parameters in Risk Based Inspection. However, when data frominter-calibration campaigns are available, the whole Receiver Operating Characteristicscurves should be used. Then the comparison of Non destructive Testing tools in terms ofcost/benefit is difficult as well as the method for optimizing a given technique. This paperpresents the αβ method that gives a new performance indicator in this context. It isapplied to the field of inspection of harbor structures.

International audience; Although a cardinal symptom of Parkinsonian disease, up to now, rigidity has been investigated much less than spasticity in hemiplegic patients. Many pathophysiological mechanisms may at least theoretically contribute to Parkinsonian rigidity, from altered viscoelastic muscle properties to inability of parkinsonian patients to relax. However, as demonstrated many years ago, motoneuron responses to muscle afferent volleys are involved in rigidity since afferent volleys are suppressed after dorsal root section. To our knowledge, homosynaptic depression (i.e. the fact that motoneuron responses to Ia afferent volleys exhibit a frequency-related depression) has not been studied in parkinsonian disease, despite the fact that in spastic patients, changes in homosynaptic depression are significantly correlated at wrist and ankle levels with the severity of spasticity. Thus, in the present series of experiments, we investigated in parkinsonian patients with chronic implantation of both subthalamic motor nuclei, the amount of homosynaptic depression at wrist and ankle levels on and off deep brain stimulation. Off deep brain stimulation, the frequency-related depression disappeared, the patients became rigid and the amount of homosynaptic depression was significantly correlated with the severity of rigidity. On deep brain stimulation, the frequency-related depression was restored and the rigidity suppressed, suggesting that homosynaptic depression is one of the mechanisms underlying rigidity in Parkinson's disease. Moreover, the unexpected finding that changes in the rigidity score and the amount of homosynaptic depression are time-locked to the onset of deep brain stimulation leads us to reconsider the mechanisms underlying changes in homosynaptic depression.

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; 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.

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.

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; 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; 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; 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.