Probabilistic evaluation to improve design of impact–echo sources

The aim of the study reported in this paper was to provide rational aid tools to quantify the performance of nondestructive testing (NDT) tools. This study focused on the quantification of the performance of impact-echo sources (steel balls of varied diameters), applied with a new, contactless robot, for duct void detection and thickness measurements in a reinforced concrete wall. Because of uncertainties during the testing, the data were analyzed in a probabilistic context, with the knowledge that on-site inspections were affected by uncertainties. The αδ method was used in this regard, where the probabilities of detection and false alarm rates were used to build receiver operating characteristic curves. The methodology was applied to data measured on the same wall with two steel ball diameters: 0.16 and 0.125 m. The quantity analyzed here was the impact-echo method (resonance) frequency. This methodology could be extended to other parameters of the impact-echo setup as well as to other NDT methods

Sustainable Maintenance and Repair of RC Coastal Structures

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

Detection of pitting corrosion in steel using image processing

This paper presents an image processing based detection method for detecting pitting corrosion in steel structures. High Dynamic Range (HDR) imaging has been carried out in this regard to demonstrate the effectiveness of such relatively inexpensive techniques that are of immense benefit to Non – Destructive – Tesing (NDT) community. The pitting corrosion of a steel sample in marine environment is successfully detected in this paper using the proposed methodology. It is observed, that the proposed method has a definite potential to be applied to a wider range of applications

Risk assessment based on performantial criterion for inspection of offshore structures in presence of large cracks

International audienceWhen performing risk analysis, it is often uneasy to find the link between limit state and consequences. This paper focuses on efficiency based limit states in case of large cracks on offshore structures. Randomness and uncertainties on loading as well as on crack measurement and detection are introduced.Les analyses de risque sont souvent délicates par manque de lien direct entre la fonction d’état et les conséquences. Cet article propose des fonctions d’état de type performantiel (déplacement) dans le cas d’apparitions de fissures traversantes dans des tubes métalliques de structures offshore. Les aléas sur le chargement, la mesure de la fissure et la performance des inspections sont intégrés dans l’analyse de risque

An image analysis based damage classification methodology

Measurement of the extent of damage in a real structure is extremely important in terms of any maintenance strategy. However, this measurement often turns out to be difficult, time consuming and error – prone. The necessity of a simple, fast and relatively inexpensive damage monitoring system with reliable measurements is growing for quite sometime. The paper proposes a camera based image analysis technique to quantify and classify damage in structures at various levels of scale. The general method has been applied to corroded plate specimens in the laboratory with the aim to identify the affected areas on a steel pile due to pitting corrosion. The method depends on the contrast of the corroded region with respect to its surroundings, performs intelligent edge detection through image processing techniques and computes each affected and closed region to predict the total area of the affected part along with its spatial distribution on a two dimensional plane. Moreover the performance of the camera allows defining a detection threshold and the so-called probability of detection (PoD) and probability of false alarms (PFA). PoD are suggested as functions of the area of the pitting for the construction of Receiver-Operating-Characteristic (ROC) curves. The methodology can be used as a tool for the owners/managers of the structure for objectively quantifying and localising the extent of pitting corrosion, rather than providing information through a subjective visual assessment. Moreover, it allows introducing the probability of detection and probability of false alarms in the decision chain and in risk analysis. The method is shown to be robust, reliable, simple and inexpensive

Reliability based assessment of structures in marine environment

The Atlantic Zone in Europe, like any coastal region, has many harbours, communication infrastructures and tourist buildings. These infrastructural elements are necessary for the economic life and sustainability of the region. The managers/owners of such structures in the region are therefore confronted with questions concerning the damage, maintenance, rehabilitation and the extent to which this maintenance or rehabilitation should be carried out. Since there are many parameters affecting the damage of a structure, it is of prime importance to know which of those parameters are guiding and what their relative importance are. Also, the effects of various critical limit states, possible conflicts between the engineer’s and the owners criteria of failure and the mutual interrelationships among possible health assessment, monitoring techniques and repair options need to be assimilated within a single probabilistic framework accounting for the various epistemic and aleatory uncertainties accompanied with such decision making process. A central factor in this decision making process is the choice of damage model of a material and its evolution in time. In this paper, a general probabilistic format is proposed for structural assessment and maintenance. A questionnaire based survey has been carried out to procure information compatible with the proposed framework with special emphasis on damage of materials in the marine environment. Parameter importance based studies on steel and concrete have been subsequently performed in order to illustrate the impacts of the interrelationships of some critical components in the proposed framework. The study provides the owners/managers with a method of establishing a choice protocol for receiver operating characteristics (ROC) of non-destructive assessment techniques of structures based on its specific needs. This methodology, in association with reliable information regarding the choice of rehabilitation of a structure at an optimised cost can be helpful for any kind of decision making process in relation to a structure

ROC dependent event isolation method for image processing based assessment of corroded harbour structures

The localisation and calibration of damage in a structure are often difficult, time consuming, subjective and error prone. The importance of a simple, fast and relatively inexpensive non-destructive technique (NDT) with reliable measurements is thus greatly felt. The usefulness and the efficiency of any such technique are often affected by environmental conditions. The definition of damage and the subsequent interpretation of the possible consequences due to the damage introduce subjectivity into an NDT technique and affect its performance. It is of great importance in terms of practical application to find out the efficiency of an NDT technique in a probabilistic way for various damage definitions and environmental conditions through the use of receiver operating characteristic (ROC) curves. Such variations of performance of an NDT tool can be predicted through simulation processes, and the test conditions conducive to good detections can be isolated and ranked according to their relative efficiency. This paper considers a camera based image analysis technique to identify,quantify and classify damage in structures at various levels of scale. The general method has been applied to identify the affected areas on aluminium due to pitting corrosion. The method depends on the optical contrast of the corroded region with respect to its surroundings, performs intelligent edge detection through image processing techniques and computes each affected and closed region to predict the total area of the affected part, together with its spatial distribution on a two-dimensional plane. The effects of various environmental factors on the quality of such images are simulated from an original photograph. The objectivity and the amount of available information, quantification and localisation and the extent of pitting corrosion are observed, together with the various constructed ROC curves. The method provides the engineer, the owner of the structure and the end-user of the NDT technique with a tool to assess the performance of the structure in an as-built condition and decide on the appropriateness of a certain NDT, under a given environmental condition and a certain definition of damage. Moreover, it allows the findings of the NDT results to be introduced in the decision chain and risk analysis

Modélisation de résultats d'inspection en présence de champs stochastiques de dégradation

Les inspections de structures existantes par des techniques de contrôles non-destructifs (CND) ne fournissent pas un résultat exact et il est courant de modéliser leur fiabilité en terme de probabilité de détection (PoD), probabilité de fausse alarme (PFA) et courbes de performance (ROC). Ces probabilités sont déterminées soit à partir de campagnes d'intercalibration soit par modélisation des densités de probabilité du bruit et du signal. Dans ce dernier cas, lorsque le bruit et le signal dépendent de la localisation sur la structure, les PoD et PFA sont des fonctions de l'espace. Cet article présente comment définir ces grandeurs lorsque le dommage et la procédure de détection sont des champs stochastiques

Improved image analysis based corrosion assessment using preprocessing techniques

The importance of non-destructive techniques (NDT) in structural health monitoring programmes is being critically felt in the recent times. The quality of the measured data, often affected by various environmental conditions can be a guiding factor in terms usefulness and prediction efficiencies of the various detection and monitoring methods used in this regard. Often, a preprocessing of the acquired data in relation to the affecting environmental parameters can improve the information quality and lead towards a significantly more efficient and correct prediction process. The improvement can be directly related to the final decision making policy about a structure or a network of structures and is compatible with general probabilistic frameworks of such assessment and decision making programmes. This paper considers a preprocessing technique employed for an image analysis based structural health monitoring methodology to identify sub-marine pitting corrosion in the presence of variable luminosity, contrast and noise affecting the quality of images. A preprocessing of the gray-level threshold of the various images is observed to bring about a significant improvement in terms of damage detection as compared to an automatically computed gray-level threshold. The case dependent adjustments of the threshold enable to obtain the best possible information from an existing image. The corresponding improvements are observed in a qualitative manner in the present study