Numerical simulation of non-load bearing lsf double walls under fire

Mestrado de dupla diplomação com a Université Libre de TunisIn recent years, light steel frame (LSF) structures, such as cold formed steel wall systems, have been used more and more, but there is a lack of adequate understanding of their fire performance. Traditionally, the fire resistance index of such non-loadbearing LSF walls, it is based on an approximate descriptive method developed on the basis of a limited fire test. Building fire safety is generally viewed as very important by the construction industry and the community as a whole. Gypsum board is widely used around the world to protect thin gauge steel frame (LSF) walls. Gypsum contains free water, which is chemically bound in its crystal structure. Plasterboard also contains gypsum (CaSO4.2H2O) and calcium carbonate (CaCO3). The evaporation of the gypsum and the decomposition of the calcium carbonate absorb heat, thus protecting the LSF wall from fire. [76] developed an innovative system of composite wall panels whose insulation of gypsum exterior walls and insulation of internal cavities (fiberglass) can improve the thermal and structural performance of LSF wall panels under conditions fire. In order to understand the performance of gypsum board and LSF wall panels under standard fire conditions, numerous experiments were carried out at the Fire Research Laboratory of the Queensland University of Technology [76] in (2018). Under standard fire protection conditions, Type X single plasterboard and non-load bearing LSF wall panels have been tested for fire protection. However, no suitable digital model has been developed to study the thermal performance of LSF walls using innovative composite panels under standard fire conditions. It is inacceptable to continue to rely on expensive and time-consuming fire tests. Based on laboratory tests, a review of the literature and a comparison of finite element analysis results of panel components, appropriate values for the important thermal properties of gypsum panels and insulating materials have been obtained [56], been proposed Sultan [56].The important thermal properties (thermal conductivity, specific heat capacity and density) of plasterboard and insulating materials were proposed [56] as a function of temperature and used in the digital model of non-load-bearing LSF wall panels. Using these thermal properties, the developed finite element model can accurately predict the values. While there are many complexities in LSF fireless wall systems, the component temperature profile reasonably predicts the temperature distribution of the systems of non-loadbearing LSF walls. This article presents some informations of the Finite Element Model of Gypsum Board and LSF Non-Loadbearing Wall Panel Components, including the Finite Element Model of Composite Panels developed [76] . This article developed by [76] is based on 2 small-scale tests to verify and compare the thermal performance of composite panels made of different thermal insulation materials of different densities and thicknesses, and offers corresponding suggestions for improving LSF walls protected by these materials to composite panel. It also provides thermal performance data of LSF wall system and demonstrates the excellent performance of LSF wall system using composite panels, uses finite elements developed from the LSF wall model to provide a new LSF wall system with higher fire resistance. The developed finite element model is particularly useful for comparing the thermal performance of different wall panel systems without the need for lengthy and expensive fire tests. This thesis presents the numerical analysis to determine the thermal response of each model throughout fire exposure using ANSYS® Multiphysics. It was verified that the use of different experimental curves to represent the evolution of the temperature inside cavities or insulating blankets was essential to obtain better numerical results. This thesis compares the fire resistance of two models (with insulating layer and without insulating layer) and come up with a parametric analysis.La sécurité incendie des bâtiments est généralement considérée comme très importante par l'industrie de la construction et l'ensemble de la communauté. Les panneaux de plâtre sont largement utilisés dans le monde entier pour protéger les murs à ossature en acier de faible épaisseur (LSF). Le plâtre contient de l'eau libre, qui est chimiquement liée dans sa structure cristalline. Les plaques de plâtre contiennent également du plâtre (CaSO4.2H2O) et du carbonate de calcium (CaCO3). La déshydratation du plâtre et la décomposition du carbonate de calcium absorbent la chaleur, protégeant ainsi la paroi LSF du feu. [76] a développé un système innovant de panneaux muraux composites dont l'isolation des murs extérieurs en plâtre et l'isolation des cavités internes (fibre de verre) peuvent améliorer les performances thermiques et structurelles des panneaux muraux LSF dans des conditions d'incendie. Afin de comprendre les performances des panneaux de plâtre et des panneaux muraux LSF dans des conditions d'incendie standard, de nombreuses expériences ont été menées au fire research laboratory de l'Université de technologie du Queensland University of Technology [76] en (2018). Dans les conditions standard de protection contre les incendies, des plaques de plâtre de type X monocouche et des panneaux muraux LSF non porteurs ont été testés pour la protection incendie. Cependant, aucun modèle numérique adapté n'a été développé pour étudier la performance thermique des murs LSF utilisant des panneaux composites innovants dans des conditions d'incendie standard. Il est inacceptable de continuer à s'appuyer sur des tests au feu coûteux et longs. Par conséquent, cette recherche a développé un modèle numérique approprié pour étudier les performances thermiques des composants de plaques de plâtre et des panneaux muraux LSF non porteurs. Sur la base d'essais en laboratoire, d'une revue de la littérature et de la comparaison des résultats d'analyse par éléments finis des composants des panneaux, des valeurs appropriées pour les propriétés thermiques importantes des panneaux de plâtre et des matériaux isolants ont été proposées par [76] . Le petit modèle en plâtre de cette étude et les résultats expérimentaux correspondants [76] . Les propriétés thermiques importantes (conductivité thermique, capacité thermique spécifique et densité) des plaques de plâtre et des matériaux isolants ont été proposées Sultan [56], en fonction de la température et utilisées dans le modèle numérique des panneaux muraux LSF non porteurs. L’article développer par [76] présente certaines informations détaillées du modèle d'éléments finis des panneaux de plâtre et des composants de panneaux muraux non porteurs en LSF, y compris le modèle d'éléments finis de panneaux composites développé par [76] . Le test expérimental développer par [76] basé sur 2 tests à petite échelle pour vérifier et comparer les performances thermiques de panneaux composites constitués de différents matériaux d'isolation thermique de différentes densités et épaisseurs . Il fournit également des données de performance thermique du système mural LSF et démontre les excellentes performances du système mural LSF utilisant des panneaux composites. Cet article utilise des éléments finis développés à partir du modèle de mur LSF pour fournir un nouveau système de mur LSF avec une résistance au feu plus élevée. Le modèle d'éléments finis développé est particulièrement utile pour comparer les performances thermiques de différents systèmes de panneaux muraux sans avoir besoin d'essais au feu longs et coûteux. Cette thèse présente l'analyse numérique pour déterminer la réponse thermique de chaque modèle tout au long de l'exposition au feu en utilisant ANSYS® Multiphysics. Il a été vérifié que l'utilisation de différentes courbes expérimentales pour représenter l'évolution de la température à l'intérieur des cavités ou des couvertures isolantes était essentielle pour obtenir de meilleurs résultats numériques

Mathematical and numerical analysis of dehydratation of gypsum plasterboards exposed to fire

International audienceIn this paper we study the well-posedness model of dehydratation of gypsum plasterboards exposed to fire. The existence of weak solution as well as uniqueness results are proved. A maximum principle is that which guarantees the existence of a solution under physical assumptions on data. The numerical solutions are presented in realistic cases

Indagini diagnostiche e procedure chimico-fisiche per i Beni Culturali

Nowadays, the concept of Cultural Heritage is deeply heart-felt; each country tries to promote and protect the artistic works standing on its territory, as they are a manifestation of culture and, at the same time, they can become an instrument of wealth for the country itself. Talking about protection and enhancement of the Cultural Heritage, it results mandatory to protect these artistic assets from degradation phenomena as they are often subjected to: these kind of phenomena are becoming even more pressing. Research in this field is putting a great deal of efforts, as the protection of artistic works is now widespread and relies on scientific techniques to prevent, treat and improve the status of the works. The doctorate project focused both on the research of new methods for the conservation and restoration of artistic works (in particular the made of inorganic materials, such as artificial and natural stones) and on the increase of knowledge on Giulio Monteverde\u2019s artistic techniques, a well-known 20th Century sculptor, by means of diagnostic tools. The cleaning method for porous materials affected by saline degradation developed during this research work is based on the international patent PCT / IB2015 / 055129, G. Torrielli, L. Gaggero, M. Ferretti owned by the University of Genoa. For brevity and clarity, during the elaborate, we will refer to this patent as "extraction method by suction" [1,2]. Currently, there are several techniques that face the salts problem: preventive solutions, such as polarity reversal devices, electromagnetic fields [3,4] and isolation of the foundations, which try to solve the problem at the origin in order to avoid that the salts enter in contact with and then penetrate into the materials. Differently, when the degradation is already underway, there are possible solutions where it is necessary to extract the present salts, such as extractive poultice applications, which are available today on the market [5,6]. These poultices are made of absorbent materials, such as clays, kaolin, talc, cellulose pulp, etc. The object of this thesis fits itself in the second group of methods for the soluble salts removal. The proposed method exploits a mechanical action in the salts extraction from the material phase: the process of removing the salts in solution towards the outside is speeded up through a micro-suction point. The first part of the work, which was carried out in the laboratory, was designed in order to define all the optimal operating parameters of the extractive method on different porous materials (such as plasters, frescoed plasters, bricks and stone materials). Once contaminated with known concentrations of saline solutions, the materials were cleaned both with the commercial technique and with the suction extractive method. The results showed that the proposed technique is faster and more efficient than traditional wraps. In the light of the obtained results, the extractive method was applied on two different real cases: a farmstead of the early \u2018900 not subject to protection restrictions, and a protected property (Santa Giulia\u2019s Church of Monastero Bormida, 18th century). In both structures, a monitoring was carried out over time to assess any saline re-growth. It emerged that the suction extractive method, as well as the wraps, allows a surface cleaning that may be however in vain, if the main deterioration source is not drained, like, for example, architectural interventions able to isolate the capillary rising of the water from the ground. The results obtained have shown that the suction extractive method can be used for the cleaning of porous materials, allowing a good removal of the salts, conveying even the ones situated in depth towards the surface. In collaboration with the Department of Earth Sciences of the University of Zaragoza, a preliminary method was developed to define saline distribution in stone materials inspired by a known technique in the geological field for land geophysical measurements [7]. The method has led to the development of a model that correlates the measured resistance of the material to the presence and distribution of salts; furthermore it could be applied even in small scale and providing non-invasive measurements for the material. In addition, another technique to be applied in the restoration field for the removal of organic coatings from surface of stone materials was investigated. This technique exploits titanium dioxide nanoparticles (TiO2). This material is well-known since many years for its photocatalytic properties, and, for this reason, it was employed in the medical, environmental and restoration field [8-10]. The photocatalytic mechanism exploits solar energy, which is able to activate the photocatalyst. When TiO2 is irradiated with a suitable wavelength, an electron-hole couple is formed and they can lead to the formation of radical species that are capable of mineralizing completely the organic substances. These features, specific of TiO2 were tested on natural and artificial stone material (brick) at the Chiostro Vecchio of Lodi, an architectural asset protected by the Superintendence of Lombardy. The structure showed a widespread aesthetic degradation due to biological coatings. In the literature the use of TiO2 for the removal of bio-degrading agents and the creation of self-cleaning films is already reported and consolidated [11-15]; therefore, in agreement with the Superintendent, it was decided to apply photocatalytic nanoparticles to test their restoring capability. The diagnostic investigations carried out on the site have shown the presence of a thin layer of natural wax on the bricks, probably due to a restoration of the nineteenth century. Before performing the tests in the real case, a laboratory study was carried out in order to identify the type of nanoparticles able to degrade the surface biological coating without affecting the underlying wax layer, which was decided to be preserved. Tests were carried out on natural wax samples treated with four different types of titanium dioxide nanoparticles: three of them were synthesized in the laboratory using the sol-gel technique (anatase TiO2, N-doped TiO2, S-doped TiO2) [16], the fourth is a commercial one (TiO2 P25 Sigma-Aldrich). The results showed that only the TiO2 P25 produced a degradation of the natural wax layer; for on-site application synthetic anatase TiO2 was chosen as it did not degrade the wax layer, but at the same time presented the best photocatalytic yield. The TiO2 application at the Chiostro Vecchio led to a good degree of cleaning of the biological coating. The last part of the work concerned the diagnostic investigation of samples taken from a plaster sculpture of Giulio Monteverde, a well-known artist of the twentieth century. The investigations allowed to widen the knowledge on a part of his unknown work, in particular on his executive technique for the realization of the plaster works and on the components of mixtures he used. The study was conducted on one of the most Monteverde famous gypsum works: "Ideality and Materialism" [17,18]. This sculpture is part of a series of gypsum artworks, a cheap material used by Monteverde for copies to be reproduced in more durable and precious materials, like marble or bronzes. With the collaboration of the Superintendence of Piedmont, it was possible to pick up samples from the surface of the \u201cMaterialism\u201d figure and perform in-depth instrumental analyses (optical microscopy, SEM-EDS electron microscopy- microprobe, FTIR spectrometry, XRD of powder) that allowed us to identify the presence of a thin layer of finishing, the sculpture "skin", composed of a mixture made of gypsum, calcite and anhydrite, which is a different mixture with respect to the underlying plaster layer. These data provided important information on Giulio Monteverde\u2019s sculptural technique, and proof of the artist\u2019s choice to create a very particular blend for the final layer of his work, perhaps for aesthetic reasons and to improve the mechanical properties of the layer itself