Effects of damage models in probabilistic assessment of structures: An illustrative example

Deterioration modelling of structures has gained significant importance in recent times in relation with structural health monitoring, rehabilitation, maintenance and decision making process. The behaviour of any deteriorating structure (or a network of structures) is extremely important while considering failure as defined from the viewpoint of both the owner/manager and the engineer. Since there are epistemic and aleatory uncertainties associated with any such process, the ideas of failure and the damage model require a probabilistic treatment. The time dependence of damage propagation very often depends on the climate conditions. On the other hand, the definition of failure by the owner and by the engineer may have different focus. These uncertainties and conflicts directly affect the assessment, optimal assessment time, repair and maintenance strategies, associated cost and the final decision regarding a structure at any given point or period of time. The paper discusses how the choice of a deterioration model (even non-functional) of a structure can affect the decision making options regarding a structure based on a probabilistic material and structure independent general framework through a simple and illustrative example. A wooden beam damaged by the growth of fungus is considered to be the benchmark problem in this regard. The damage is modelled to be comprised of two stages – the initiation and the propagation period. A Monte Carlo simulation investigates the effects of environmental parameters, active regions in time, conflicts of owner’s and engineer’s criteria and the critical location in a structure in terms of possible destructive or non destructive instrumentation

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

Improving the reliability of on-site concrete strength estimation with non-destructive techniques

The non-destructive assessment of concrete strength in existing structures is a complex issue. While many standards exist addressing the way non-destructive measurements must be carried out, few exist for the strength assessment itself. Many questions remain unanswered, like for instance the reliability of the strength estimation, the possibility of estimating the concrete variability, or the advantages of combining several non-destructive techniques. These problems have been tackled by a recent RILEM committee (TC ISC 249) whose Guidelines and Recommendations are to be released soon. This paper details their main innovations and how they are expected to improve the engineering practice and the reliability of strength estimation in existing structures

Lifetime of timber notched beams under several random modelling of french climates

The mechanical response and durability of building materials is highly influenced by the atmospheric conditions. Temperature and air humidity have a great influence on the transfer of water and contaminants in the porous structure of these materials. This paper focuses on the effects of moisture content and/or moisture dynamics which are even more important when rupture is due to crack. Climatic variations are simulated and a lifetime model is proposed. The “climat” method consists in processing a wide amount of meteorological records from four French sites covering different climates, in order to identify their statistical properties, identify their time auto-correlation characteristics, be able to rebuild synthetic signals with the same or different characteristics. The generic model is able to reproduce a very large amount of simulations, which is necessary for reliability or statistical analyses. The lifetime model predicts the incubation time and the time of crack propagation until the failure. As temperature has a smaller influence on the time to failure than relative humidity, its effects are not directly taken into account in the model. Predictions of the proposed model for various air humidity simulations are compared with creep test results obtained on notched LVL beams under various climatic conditions

Gestion des risques dans les projets de construction par la simulation multi-agent

Les dernières années ont connu un fort développement de la recherche sur le domaine de la gestion des risques dans les projets de construction. Les projets de construction sont touchés par de nombreux risques (accident sur un chantier, mal façons, problèmes de communications entre acteurs) induisant des retards et des coûts importants. Au centre de ces risques se placent les acteurs (maitre d’œuvre, maitre d’ouvrage…) qui par leurs décisions, leurs comportements ou leurs méthodes de travail peuvent avoir une influence sur eux. Chaque acteur a ses propres risques et sa propre vision sur les risques du projet. Pour ces raisons, il peut être difficile de modéliser les risques projet afin de les maitriser. Dans cet article, un modèle à base d’agents (SMACC) est proposé pour analyser les risques du projet. Il propose par le recours à la simulation multi-agent couplée à une approche stochastique d’évaluer les conséquences des risques sur le projet et cela pour chaque acteur. Ce modèle dynamique permet de prendre en compte aussi l’évolution des risques durant tout le projet ; cette évolution étant conditionnée par toutes les composantes du projet (acteurs, ressources, avancement des tâches…) et par les décisions prises par les acteurs pour y répondre. Il est possible de modéliser différentes stratégies (exigences contractuelles, mesures liées à la sécurité…) au travers des paramètres d’entrée et de simuler leur impact sur le projet. SMACC permet ainsi d’établir des indicateurs qui peuvent servir de critères dans le cadre d’un processus d’aide à la décision afin d’aider un gestionnaire de projet à choisir la stratégie la plus pertinente pour la conduite du projet