Daniel Boissier

Probability-based assessment of dam safety using combined risk analysis and reliability methods – application to hazards studies

Dam safety assessment is a major challenge for engineers specialising in hydraulic works. It is now standardised in regulations providing for hazards studies using probability-based risk analysis procedures. Dam safety probability-based assessment includes two key scientific issues: the modelling of complex mechanisms that occur within the works, and a probability-based assessment of structural safety. This paper introduces a combined application of risk analysis and dam reliability methodologies. This combination required the completion of our work on the adaptation of risk analysis methods to dams, and on the probability-based modelling of strength and loading input data for a reliability-based analysis. These methodologies are then implemented as part of a hazards study on a roller-compacted-concrete gravity dam.

Évaluation des ouvrages hydrauliques de génie civil

This paper reviews Cemagref (Centre national du machinisme agricole, du genie rural, des eaux et des forets) research on assessment of hydraulic works, especially on their performance and safety. A generic functional model has been developed, using reliability methods, to represent the various mecanisms acting on different hydraulic works (gravity and embankment dams, fluvial dikes, etc.). Collecting and analyzing data on the failure of these works allowed us to define structural indicators and the rules for their assessment. Performance indicators for hydraulic works were created through multicriteria aggregation methods; various results were thus obtained. A database of knowledge relating to mechanisms and histories of dam ageing has been produced and constitutes a useful aid for consulting civil engineers. Methods and tools have been developed to assess the performance of fluvial dikes and to assist managers in planning maintenance operations. Similar research is under way on embankment dams and will p...

Approches de l'analyse de risques en génie civil Exemple des barrages

ABSTRACT Considering risk analysis in the industrial context we first present the main concepts dealing with risk and its analysis. Secondly we build up a synthesis of the different existing approaches: internal methods including physical and functional modelling, external methods including statistical approach and expertise. For each of them, we list the main applications in civil engineering and we develop their use in the peculiar case of dams.

Development of a Scenario-based DSS for Dam Ageing Diagnosis

This paper presents the Cemagref work in the field of diagnosis aid applied to dam ageing. The context is a portfolio of 250 dams under the supervisory of the environment ministry and involving public safety. These dams are characterised by a relative heterogeneity in their conception, age and management modes. First, the paper presents this dam portfolio. Our approach proposes to capitalise on feedback and expert knowledge, in order to improve dam diagnosis. Our work has started with computer researches, in order to model expert’s process of reasoning by dam ageing scenarios. We have produced a decision making aid system for dam ageing diagnosis. This system is able to manage historic and ageing scenario databases. Then, we have developed with LERMES/CUST a dam degradation model in order to build up the scenarios. Our methodology is based on functional modelling and FMEA method. Our main goal is to build up a dam ageing scenario database and to manage this database with the decision making tools.

Service-life assessment of building components: application of evidence theory

This paper deals with the assessment of the service life of in-service building components subjected to known environmental and usage conditions. This assessment is complex because of two primary features. First, the assessment has to be carried within a multiscale context: a geometric scale that ranges from the material or elemental to building scale; a range in the complexity of the degradation (phenomena that varies from a single phenomenon to the consideration of several degradation scenarios); a range of possible performance requirements, from one function to several; and consideration, as well, to the time over which the process is carried out that may span from the design stage to that of management and repair. Second, this assessment must also take into consideration the availability and features of service-life data that by nature is heterogeneous, imprecise, uncertain, and incomplete. In this context, a comprehensive methodology is developed using all available data on service life derived from ...

Assessment of hydraulic load acting on dams including filling variability and stochastic simulations

ABSTRACT Standard practice in dam engineering is to consider only the maximum reservoir level governing the maximum hydraulic loading. This article presents a probability method for modelling reservoir level and the corresponding load on the dam. It uses multiple randomly-generated flood hydrographs to investigate the effect of reservoir level variability. The method was tried on three operational dams to assess its utility as an operational dam safety analysis method.

Etude de la sûreté de fonctionnement d'un aménagement hydraulique de génie civil : Application à des ouvrages de protection contre les inondations de la ville de Nîmes

ABSTRACT Cemagref and ISL consulting engineers produced for Nîmes city (France) a reliability study concerning a hydraulic works system, composed of several dams, singular civil works, canals and collectors networks, and intended to ensure protection against floods. This study constitutes one of the first quantitative reliability studies of a hydraulic works system realized in France. This article presents the step and the methodologies used in a reliability quantitative analysis. The methodological developments are illustrated all along the text through this remarkable application.

Code performance assessment: application to the pull-out strength of concrete

This paper deals with the investigation into the best fitted program for solving a particular problem. We present a general method to assess the efficiency of a code in the general context where both experimental results (due to problems of experimental reproducibility and/or sample size) and theoretical results (predicted by the computer code) are uncertain. This method is based on the use of fuzzy sets to represent partial results and on a method to aggregate them into a global confidence degree. This method is applied to the problem of the pulling steel plugs out of a block of concrete or masonry, the code being based on limit analysis theory.RésuméCette publications s’intéresse à la qualification d’un code de calcul à la résolution d’un problème spécifique. On présente une méthode générale pour estimer le niveau de performance d’un code de calcul dans le contexte réel où à la fois les résultats fournis par le code et les résultats fournis par l’expérimentation sont incertains (reproductivité de l’expérience, taille de l’échantillon). Cette méthode est basée sur la modélisation des résultats partiels par des sous ensembles flous et leur agrégation en degré de confiance global. Cette méthode est appliquée au problème de la modélisation par un code d’analyse limite des ancrages par cheville métallique dans le béton ou dans les blocs de maçonnerie.

Aide à la conception de fondations de bâtiments : un modèle d'expertise

ABSTRACT This paper has for general context the development of a computer assisted design tool for building foundation. Our objective is to propose at the designers disposal the treatments and the representation of the data appropriate for the design context for the currently studied project. This design context depends on the design stage for the buiding, the available knowledge of soil properties, the design team and the design method. Since the generating process called largely upon the know how of the designers themselves, we have followed the knowledge elicitation approach with its formalisation. In the paper, we present more specifically the formalisation phase. It is based on the buiding of an expertise model structured on four levels entitled « Strategy. Task, Inference, Domain ». Each level with its specific results has been detailed.