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Évaluation probabiliste de la fiabilité structurelle des digues fluviales à partir du jugement d’expert / Probabilistic evaluation of the structural reliability of river levees based on expert judgmentHathout, Michel 03 April 2018 (has links)
Les digues de protection contre les inondations sont d’une importance stratégique incontournable pour la sécurité des personnes et des biens. Une meilleure connaissance de leur fiabilité structurelle constitue un enjeu majeur pour les ingénieurs et pour les gestionnaires de ces ouvrages afin de répondre aux réglementations en vigueur et potentiellement les faire évoluer. La réglementation en France relative à la sûreté des ouvrages hydrauliques exige la réalisation d’études de dangers, au sein desquelles les démarches probabilistes d’évaluation de la sécurité prennent une place de plus en plus importante. De par la complexité de leurs mécanismes de rupture et l’absence de condition d’état-limite précis pour certains mécanismes de défaillance tels que l’érosion interne, la surverse ou l’affouillement, le calcul d’une probabilité de défaillance par des approches quantitatives demeure à ce jour impossible. Les digues induisent des problématiques particulières pour l’évaluation de leur fiabilité structurelle où l’intervention d’experts s’avère nécessaire et centrale. Ceux-ci doivent procéder à l’interprétation des données disponibles et la prise en compte de leurs incertitudes, pour pouvoir ensuite évaluer la fiabilité structurelle de digues en termes de probabilité de défaillance. L’objectif de la thèse est l’élaboration d’une démarche complète d’aide à l’évaluation probabiliste de la fiabilité structurelle des digues à partir du jugement expert. Une démarche scientifiquement justifiée pour le recueil et l’exploitation des évaluations expertes, incertaines mais quantitatives, de la fiabilité structurelle des ouvrages, sous la forme d’une probabilité de défaillance ou d’un coefficient de sécurité, assorti(e) d’une marge d’incertitude probabiliste. Afin de répondre à cet objectif, deux démarches ont été développée, « EiCAD » et « EiDA », toutes reposant (dans des ordres différents) sur les phases suivantes :- Une phase d’élicitation individuelle des avis experts (Ei) permettant le recueil des évaluations expertes probabilistes par la construction d’un formulaire de questionnement ;- Une phase de calibration (C) permettant de pondérer les évaluations expertes en fonction des degrés de précision et de justesse ;- Une phase d’agrégation (A) permettant une prise en compte simultanée de plusieurs évaluations expertes probabilistes ;- Une phase de débiaisage (D) permettant de traiter les biais susceptibles d’entacher les évaluations expertes probabilistes. Les démarches développées ont été mises en œuvre sur des cas de digues du Drac, dans l’agglomération grenobloise, pour évaluer la probabilité de défaillance, par jugement expert, vis-à-vis de mécanisme de rupture par glissement et par érosion interne / River levees as protective measures against flooding are a matter of utmost strategic importance for the security of people and property. A better knowledge of their structural reliability is a major challenge for engineers and managers of these structures in order to meet current regulations and potentially develop them. In France, the regulations relating to the safety of hydraulic structures require the realization of hazard studies, in which probabilistic safety evaluation procedures take on a more and more important role. Due to the complexity of their failure mechanisms and the lack of a specific condition of limit-state for some failure mechanisms such as internal erosion and overtopping or scour, calculating a probability of failure by quantitative approaches remains impossible to this day. Levees induce specific problems in evaluating their structural reliability where expert intervention is necessary and pivotal. They must interpret the available data and take into account the uncertainties in their analysis, in order to evaluate the structural reliability of levees in terms of probability of failure. The aim of the thesis is to develop and elaborate a complete approach for supporting probabilistic evaluation of structural reliability of levees based on expert judgments. It is designed as a scientifically justified approach to collect and use uncertain but quantitative expert evaluations of structural reliability, in the form of a failure probability or a safety factor, accompanied by a margin of probabilistic uncertainty. To meet this goal, two approaches have been developed, "EiCAD" and "EiDA" composed of the following phases (in different orders):- individual elicitation phase of expert judgment (Ei) allowing the collection of probabilistic expert evaluations by a constricted questionnaire ;- calibration phase (C) to weigh the probabilistic expert evaluations elicited depending on the degrees of precision and accuracy that can be provided;- aggregation phase (A) during which the probabilistic expert evaluations elicited by several experts are taken into account ;- debiasing phase (D) during which biases that may affect the probabilistic expert evaluations are removed. The developed approaches have been implemented for the cases of Drac levees, located in the Grenoble agglomeration, to assess the probability of failure, by expert judgment, with regard to sliding and internal erosion mechanism of failure
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Modelando atualizaÃÃo bayesiana com muitos nÃo-atualizadores: o caso do prÃprio homicÃdio subjetiva risco de vitimizaÃÃo / Modeling bayesian updating with many non-updaters: the case of own subjective homicide victimization riskYuri Lacerda Costa 27 March 2015 (has links)
nÃo hà / Nosso principal objetivo neste estudo à investigar o papel da heterogeneidade na atualizaÃÃo,
depois de um choque de informaÃÃo, do risco subjetivo sobre vitimizaÃÃo de homicÃdio.
Nesse sentido, os dados utilizados neste trabalho tambÃm atestam a superestimaÃÃo do
crime encontrada na literatura. A novidade à que os entrevistados receberam um choque
de informaÃÃo que consiste na taxa oficial de homicÃdios, mas a grande maioria deles
mantÃm a mesma percepÃÃo inicial. Ao propor um modelo de Update Bayesiano permitindo
que nenhuma atualizaÃÃo fosse realizada, dois modelos foram desenvolvidos: um Tobit
modificado e um modelo Hurdle de dois nÃveis. Assim como em estudos anteriores, nossos
resultados mostraram que poderÃamos prosseguir com uma abordagem de Update Bayesiano.
Ainda, quanto mais altas as respostas iniciais eram definidas, mais propensos os indivÃduos
estavam em proceder uma mudanÃa de percepÃÃo. AlÃm disso, fundamentalmente,
pudemos racionalizar a decisÃo de nÃo revisar as respostas seguindo um argumento de
qualidade/credibilidade da informaÃÃo percebida. Descobrimos que os participantes mais
velhos e as mulheres sÃo mais relutantes nÃo apenas em alterar as respostas iniciais, mas
tambÃm na escolha do nÃvel da nova resposta, em caso de mudanÃa. Outra conclusÃo feita
foi que o nÃvel educacional dos entrevistados era insignificante em nosso exercÃcio. De fato,
o nÃvel educacional do entrevistador teve um papel fundamental em ambas decisÃes de
mudanÃa e magnitude de revisÃo. Finalmente, nossos resultados tambÃm levantaram fortes
evidÃncias sobre aspectos de homofilia. A ocorrÃncia de uma correspondÃncia em gÃnero
entre entrevistadores e entrevistados teve o maior impacto sobre a decisÃo de mudar e na
magnitude da atualizaÃÃo neste estudo. / Our main purpose in this study is to investigate the role of heterogeneity into the update
of subjective homicide victimization risk after an informational shock. In this sense, the
data used here also attests the crime overestimation found in the literature. The novelty
is that our respondents faced an informational shock consisting in the official homicide
rate, but the vast majority of them keeps the same initial perception. In proposing a
Bayesian Update model allowing that no update takes place, two models were developed:
a modified Tobit and a two-tiered Hurdle model. In accordance with previous papers, our
results showed that we could proceed with a Bayesian Update approach. Also, the higher
initial responses are set, more likely individuals are in proceeding a change in perceptions.
Furthermore, fundamentally, we could rationalize a non-updating decision following a
perceived informational quality/credibility argument. We found that older participants
and females are more reluctant not only to change initial responses, but also to choose the
level of the new response, in case of an update. In addition, respondentsâ level of education
was insignificant in our exercise. In fact, interviewersâ level of education had a key role
in both the changing and updating magnitude decisions. Finally, our results also raised
strong evidence on homophily aspects. The occurance of a matching in gender between
interviewers and interviewees had a major impact on the decision to change and in the
magnitude of the update in this study.
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