A Priori Modelling of Fire Test One

Chapter 10 in the book: The Dalmarnock Fire Tests: Experiments and Modelling, Edited by G. Rein, C. Abecassis Empis and R. Carvel, Published by the School of Engineering and Electronics, University of Edinburgh, 2007. ISBN 978-0-9557497-0-4An international round-robin study of fire modelling was conducted prior to the Dalmarnock Fire Tests in order to assess the state-of-the-art of fire modelling in real scenarios. The philosophy behind the Dalmarnock Fire Tests was to provide instrumentation density suitable for comparison to field models and designed the scenario for maximum test reproducibility. Each participating team independently simulated a priori the test using a common detailed description of the compartment geometry, fuel packages, ignition source and ventilation conditions. The aim of the exercise was to forecast the test results as accurately as possible, and not to provide an engineering analysis with adequate conservative assumptions or safety factors. The modelling results and experimental measurements are compared among themselves, allowing for conclusions on the robustness, reliability and accuracy of current modelling practices. The results indicate large scatter and considerable disparity among predicted fires and also differing from the experimental data. The Dalmarnock Fire Test One was benchmarked against a second test to establish the potential experimental variability. The scatter of the simulations is much larger than the experimental error and the experimental variability. The study emphasises on the inherent difficulty of predicting fire dynamics and demonstrates that the main source of scatter is originated in the many degrees of freedom and the uncertainty in the input parameters. The conclusions from the study are made public to encourage debate and exchange of views on the topic of fire modelling

Round-robin study of a priori modelling predictions of the Dalmarnock Fire Test One

Peer-reviewed journal paper published in 2009 about the international modelling exercise conducted in 2006.An international study of fire modelling was conducted prior to the Dalmarnock Fire Test One in order to assess the state-of-the-art of fire simulations using a round-robin approach. This test forms part of the Dalmarnock Fire Tests, a series of experiments conducted in 2006 in a high-rise building. The philosophy behind the tests was to provide measurements in a realistic fire scenario involving multiple fuel packages and non-trivial fire growth, and with an instrumentation density suitable for comparison with computational fluid dynamics models. Each of the seven round-robin teams independently simulated the test scenario a priori using a common detailed description of the compartment geometry, fuel packages, ignition source and ventilation conditions. The aim of the exercise was to forecast the fire development as accurately as possible and compare the results. The aim was not to provide an engineering analysis with conservative assumptions or safety factors. Comparison of the modelling results shows a large scatter and considerable disparity among the predictions, and between predictions and experimental measurements. The scatter of the simulations is much larger than the error and variability expected in the experiments. The study emphasises on the inherent difficulty of modelling fire dynamics in complex fire scenarios like Dalmarnock, and shows that the accuracy to predict fire growth (i.e. evolution of the heat released rate) is, in general, poor

Détermination des conditions d'échauffement de structure extérieure à un bâtiment en situation d'incendie

This work is concerned with the study of the heating conditions of external members during a fire. The first chapter of the thesis is about a bibliographical synthesis on compartment fires, especially on the topic of flames flowing out through compartment openings. It was decided to use an advanced fire simulation tool, in order to study the main parameters affecting the characteristics of external flames. Chapter 2 is devoted to a comprehensive description of the CFD tool used for that purpose, describing its key features, assumptions, abilities and weaknesses. Chapter 3 is about the validation of this numerical tool, based on experimental cases of increasing complexity. The study of the main parameters affecting the characteristics of external flames is performed in chapter 4, by using numerical as well as experimental results. This work has made it possible to carry out the checking and the extension of a simplified calculation method intended to predict the heating conditions of external members. The practical application of this task is given in chapter 5. It consisted in gathering all the results in a new simplified model aimed at providing a realistic estimation of transient heat fluxes to external members during a fire.Ce travail de thèse est consacré à l'étude des conditions d'échauffement des éléments de structure situés à l'extérieur des bâtiments en feu. Une synthèse bibliographique sur les feux de compartiment et plus particulièrement sur la problématique de la sortie de flammes par les ouvertures des locaux en feu a été réalisée. Un outil de simulation numérique avancé a été mis en oeuvre pour étudier les paramètres principaux affectant les caractéristiques des flammes extérieures. Cette tâche a nécessité au préalable la prise en main et le développement d'un modèle CFD de simulation numérique du feu, ainsi que sa validation sur des cas expérimentaux de complexité croissante. A l'étude numérique de la sortie de flammes d'un local en feu est venue s'ajouter une partie expérimentale concernant l'effet du vent sur les flammes extérieures. L'étude des flammes extérieures a permis de procéder à la vérification et à l'extension d'une méthode de calcul simplifiée destinée à prédire les conditions d'échauffement des éléments de structure situés à l'extérieur des bâtiments. L'application pratique de ce travail a consisté à regrouper dans un nouveau modèle global les résultats obtenus à partir de la synthèse bibliographique et des études numériques et expérimentales

A multiaxial concrete model for applications in structural fire engineering

peer reviewedTemperature-dependent material models are required in numerical softwares dedicated to the nonlinear analysis of structures in fire. Although structural concrete is widely used in civil engineering, proper modelling of its thermo-mechanical behaviour remains a challenging issue for engineers mainly because of the complexity of the phenomena that result from the microcracking process in this composite material and because of the lack of numerical robustness of the models. This paper presents a new multiaxial concrete model developed for the analysis of concrete structures in fire. The multiaxial model is based on a plastic-damage formulation and incorporates an explicit term for transient creep strain. After implementation in a finite element software for structural fire engineering calculations, numerical simulations have been performed to highlight the ability of the model to capture some of the main phenomena that develop in concrete (permanent strains, degradation of the elastic properties, unilateral effect) as well as the ability to be used for the fire analysis of large-scale structural elements