IFSTTAR

Versailles, France
Versailles, France

Time filter

Source Type

Orcesi A.D.,IFSTTAR | Frangopol D.M.,Lehigh University
Engineering Structures | Year: 2011

Management of bridges under uncertainty is an important issue for stakeholders. The use of probabilistic approaches enables one to consider uncertainties in the structural deterioration, assessment, and maintenance processes. Combined with optimization techniques, it is possible to determine management strategies that simultaneously minimize failure, assessment, maintenance, and rehabilitation costs. Nevertheless, there is a strong need in developing practical and efficient frameworks that enable stakeholders to optimize future allocation of budgets for facilities under uncertain structural parameters. In particular, providing an approach that is in agreement with stakeholders constraints still remains a challenge. Moreover, the use of structural health monitoring (SHM) in future management frameworks, to update structural performance, still needs further development. The objective of this paper is threefold: (a) provide management strategies in agreement with fixed budgets, (b) provide management strategies that consider the time delay between the assessment and the intervention schedule, and (c) include information provided by SHM in the decision process and analyze the impact of monitoring strategies on the structural analysis accuracy. An event tree based approach is proposed to consider various uncertainties in the decision process. Optimal solutions are associated with multiple criteria such as minimum expected failure cost, minimum expected inspection/SHM/maintenance costs, maximum agreement of expected inspection/SHM/maintenance costs to available budgets, and maximum accuracy of monitoring results. The approach is illustrated on an existing highway bridge. © 2011 Elsevier Ltd.


Omikrine Metalssi O.,IFSTTAR | Ait-Mokhtar A.,University of La Rochelle | Turcry P.,University of La Rochelle | Ruot B.,CSTB
Construction and Building Materials | Year: 2012

This paper presents the consequences of the carbonation phenomenon in the case of a mortar with cellulose ether as admixture on its mechanical properties, microstructure and length variations. Carbonation was found to improve mechanical strengths and decrease the global porosity with modifying the pore size distribution. The latter is beneficial regarding durability. However, carbonation also led to an increase of shrinkage, and thus to a probable increase of cracking. Carbonation and shrinkage kinetics could be slowed down by sheltering the material from carbonation during hardening. © 2012 Elsevier Ltd. All rights reserved.


Granie M.-A.,IFSTTAR | Papafava E.,IFSTTAR
Transportation Research Part F: Traffic Psychology and Behaviour | Year: 2011

Gender differences in accidentology, notably on roads, are well documented and current research in social psychology tends to explain these differences by gender stereotypes, notably the association of risk-taking with social expectations concerning masculinity. To date, however, little research has explored gender stereotypes associated with vehicle driving. Beliefs about driving by men and women, as well as the effect of the age and gender of the perceiver, were explored using the free association method with 599 preadolescents and adolescents between 10 and 16 years of age. The results show that gender stereotypes are indeed associated with driving from the age of 10. While the representation of male drivers is already stable at this age, the representation of female drivers appears to develop with age. Furthermore, there is a notable in-group serving bias, but only among girls. The results are discussed in terms of an essentialist representation of genders, in-group/out-group relations, age differences in gender stereotypes associated with driving, and practical consequences on driver's training and socialization to risk-taking. © 2011 Elsevier Ltd. All rights reserved.


Tom A.,IFSTTAR | Granie M.-A.,IFSTTAR
Accident Analysis and Prevention | Year: 2011

Male pedestrians are over-represented in road crashes. Among pedestrians, males violate more rules than females do. For now, it is not known whether gender differences in pedestrian behaviors only concern rule compliance. The objective of this study was to explore gender differences in pedestrian rule compliance and in gaze targets before and during crossing. 400 adult pedestrians were observed at two signalized and two unsignalized crossroads, using a taxonomic observation grid which detailed 13 behavioral categories before, during and after crossing. The results show that the temporal crossing compliance rate is lower among male pedestrians but spatial crossing compliance does not differ between genders. Furthermore, different gaze patterns emerge between genders before and during crossing, notably as women particularly focus on other pedestrians during these two periods whereas men focus on vehicles. Moreover, females' gazes vary with the type of crossroads, but males' gazes do not. Spatial crossing compliance and gaze targets are furthermore modulated by the crossroad configuration. These results are discussed in terms of pedestrian visual strategy and compliance. © 2011 Elsevier Ltd. All rights reserved.


Belaroussi R.,IFSTTAR | Milgram M.,University Pierre and Marie Curie
Expert Systems with Applications | Year: 2012

Face localization is the first stage in many vision based applications and in human-computer interaction. The problem is to define the face location of a person in a color image. The four boosted classifiers embbeded in OpenCV, based on Haar-like features, are compared in terms of speed and efficiency. Skin color distribution is estimated using a non parametric approach. To avoid drifting in color estimate, this model is not updated during the sequence but renewed whenever the face is detected again, that gives the ability to our system to cope with different lighting conditions in a more robust way. Skin color model is then used to localize the face represented by an ellipse: connected component segmentation and a statistical approach, namely the coupled Camshift of Bradsky, are compared in terms of efficiency and speed. The pursuit algorithms are tested on various video sequences, corresponding to various scenarios in terms of illumination, face pose, face size and background complexity (distractor effects). © 2011 Elsevier Ltd. All rights reserved.


Cord A.,IFSTTAR | Chambon S.,LUNAM University
Computer-Aided Civil and Infrastructure Engineering | Year: 2012

The state of roads is continuously degrading due to meteorological conditions, ground movements, and traffic, leading to the formation of defects, such as grabbing, holes, and cracks. In this article, a method to automatically distinguish images of road surfaces with defects from road surfaces without defects is presented. This method, based on supervised learning, is generic and may be applied to all type of defects present in those images. They typically present strong textural information with patterns that show fluctuations at small scales and some uniformity at larger scales. The textural information is described by applying a large set of linear and nonlinear filters. To select the most pertinent ones for the current application, a supervised learning based on AdaBoost is performed. The whole process is tested both on a textural recognition task based on the VisTex image database and on road images collected by a dedicated road imaging system. A comparison with a recent cracks detection algorithm from Oliveira and Correia demonstrates the proposed method's efficiency. © 2011 Computer-Aided Civil and Infrastructure Engineering.


Orcesi A.D.,IFSTTAR | Frangopol D.M.,Lehigh University
Journal of Structural Engineering | Year: 2011

A model using lifetime functions is used to evaluate the probability of survival of bridge components. The possible outcomes associated with nondestructive inspections (NDIs) are incorporated in an event-tree model. Each time a bridge component is inspected, different decisions can be made. The use of a lifetime function for each component of the structural system enables one to express the probability that the component survives. In theory (i.e., perfect inspection), each NDI should be associated with two possible outcomes: survival or failure. In the first case, no damage is detected and the probability density function of time to failure is updated knowing that the component has survived until the inspection. In the second case, damage is detected and maintenance action is planned. In practice, NDIs are subjected to uncertainties (i.e., imperfect inspections) and detecting or not detecting damage depends on the inspection quality (i.e., probability of detection). For poor-quality inspections, there is a significant risk to overestimate the probability of safe performance. The aim of this paper is to provide a practical methodology for determining optimal NDI strategies for different components of steel bridges. The different types of inspections considered in this paper are visual, magnetic particle, and ultrasonic. An economic analysis is performed and NDI strategies are optimized by simultaneously minimizing both the expected inspection/maintenance cost (i.e., the sum of inspection and maintenance costs) and the expected failure cost. The proposed approach is applied to an existing steel bridge. © 2011 American Society of Civil Engineers.


Kane M.,IFSTTAR | Artamendi I.,Aggregate Industries UK Ltd. | Scarpas T.,Technical University of Delft
Wear | Year: 2013

This work focuses on the relation between the mineralogical composition of aggregates and their capacity to generate adequate friction between the road surface and the tyre after the polishing action of traffic. Three different types of aggregate namely greywacke, granite and limestone were used in the study. Petrographic examination of the aggregates was carried out using optical microscopy. The Wehner-Schulze apparatus was used to determine the evolution of friction with polishing cycles of both aggregates and asphalt specimens. A new aggregate hardness parameter was introduced based on the mineralogical composition and the hardness of the individual minerals. This hardness parameter was then related to friction coefficients measured on aggregate specimens after 180.000 polishing cycles. Initial results indicated that this new aggregate hardness parameter is a good indicator of the capacity of an aggregate to retain good friction levels. Changes in the microtexture of the aggregate during polishing were also analysed using a confocal microscopy technique. Microtexture measurements confirmed different levels of polishing for the different types of aggregates. © 2013 Elsevier B.V.


Deniau V.,IFSTTAR
IEEE Electromagnetic Compatibility Magazine | Year: 2014

The European project SECRET studies the security of the railway network against Electromagnetic Attacks. The SECRET consortium involves 10 partners from five European countries. The project is coordinated by IFSTTAR which is the French institute of science and technology for transport, development and network. The project started in August 2012 for a duration of 36 months. © 2012 IEEE.


Olsson N.,Lund University | Baroghel-Bouny V.,IFSTTAR | Nilsson L.-O.,Lund University | Thiery M.,IFSTTAR
Cement and Concrete Composites | Year: 2013

Non-saturated ion diffusion properties of cementitious materials were evaluated in an experimental study. To assess these properties, resistivity measurements have been performed on mortars with different binders (ordinary Portland cement - OPC, OPC with 5% silica fume, 40% slag and 70% slag, respectively) and different water-to-binder ratios (w/b, 0.38 and 0.53). Specimens have been conditioned to eight different climates with relative humidity (RH) from 100% to 33% RH in order to assess an effective diffusion coefficient. The results from the resistivity measurements have been corrected for changes of the conductivity of the pore solution when drying to different degrees of saturation. The diffusion coefficients for Portland cement binders within the range 100-59% RH are presented. They showed that the diffusion coefficient of the mortar with high w/b ratio was higher at high RH, but at low RH the opposite trend was found. By comparing these results with the corresponding desorption isotherms, it is shown that the diffusion coefficient for the two w/b ratios have the same dependency on the degree of saturation. © 2013 Elsevier Ltd. All rights reserved.

Loading IFSTTAR collaborators
Loading IFSTTAR collaborators