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Au regard des ouvrages bois du Génie Civil placés en extérieur, les problématiques de durabilité sont principalement liées aux risques d’attaques biologiques tempérées par les conditions d’humidité environnementale. Naturellement durable en classe de risque 3, l’utilisation du Douglas demande des traitements particuliers et complexes sous des expositions plus sévères à l’humidité, et ce, avec des impacts environnementaux plus ou moins marqués. Dans le cadre de la chaire ‘Ressources Forestières & Usages du Bois’ mise en place par l’Université de Limoges et en partenariat avec l’INRA d’Orléans, le PIAF et l’Institut Pascal de Clermont-Ferrand, nous présentons une approche originale avec comme objectif d’accroitre ce degré de durabilité naturelle afin de limiter le recours systématique aux traitements de préservation. Cette approche de la durabilité propose une transversalité entre patrimoine génétique des différentes familles de Douglas et la durabilité en structure en employant, comme ‘marqueur’, le comportement hygroscopique du matériau. L’objet de ce travail consiste à caractériser les propriétés hygroscopiques de quatre génotypes de Douglas et, plus précisément, les propriétés de diffusion hydrique et d’isothermes de sorption. Cette étude statistique alimentera une base de données dont l’ambition est d’isoler un génotype en lien avec des caractéristiques d’inertie hydrique limitant, à la fois, les pics hydriques et la pénétration du front hydrique dans les éléments massifs structuraux. / For exterior civil engineering works, durability issues are mainly linked to the risks of biological attacks tempered by environmental moisture conditions. Douglas fir, which is naturally sustainable in risk class 3, requires complex treatments when it is exposed to severe moisture condition, a treatment which have significant environmental impacts that remains marked even today. In the context of the Chair, 'Resources Forestières & Usages du Bois' created by the University of Limoges and in partnership with the INRA of Orléans, the PIAF and the Pascal Institute of Clermont Ferrand, we present an original approach whose objective is to increase this degree of natural durability, and to limit the systematic use of preservation treatments. This approach to durability proposes a coupling between the genetic heritage of different Douglas families and the structural durability by using, as a 'marker', the hygroscopic behavior of the material. The aim of this work is to characterize the hygroscopic properties of four Douglas genotypes, and more precisely, the properties of water diffusion and sorption isotherms. This statistical study feeds a database with the objective is to isolate a genotype in relation with limiting hydric-inertia characteristics, both the water peaks and the penetration of the water front in the structural massive elements.

It is common practice in the analysis of structural frames, to either assume that the joints are pinned or rigid. In fact the real behaviour of a joint is neither pinned nor rigid, and lies somewhere between the pinned and rigid assumption. This is referred to as the semi-rigid behaviour. Semi-rigidity not only refers to the rotational behaviour of the joint as commonly studied, but also in axial and shear actions. The moment distribution between pinned and rigid analysis differs substantially and therefore a more accurate method of modelling the semi-rigid joint is necessary to predict the overall structure response. The level of semi-rigid behaviour varies in different joints due to the material, construction and type of connector. The degree of semi-rigidity can be determined through physical tests. The type of joint for this study is the Metal Plate Connector (MPC) for timber trusses, 6 chosen connector used in residential trusses. An extensive test program was carried out in this study. Four different types of joints of a Queen truss were tested. In addition, the effect of combined loads on the joint characteristics was investigated. The loading arrangement in the tests allowed independent control of the bending moment and axial load. A novel approach is adopted to measure displacement, using high-resolution digital photogrammetry and specially developed software. The data produced gave details of timber movement in cartesian co-ordinates and measurement of plate deformation. From these tests, semi-rigid bending moment and axial stiffness values were determined for use in the theoretical study. An attempt to measure shear stiffness is also presented. Further tests were carried out on full-scale trusses under two different load conditions. The theoretical work comprises two approaches to truss modelling. The first is an automated structural analysis program, which accounts for non-linear semirigid joint characteristics derived from the joint tests using the Foschi power function. The effects of stability and geometrical non-linearity are also implemented into the analysis. The second approach calculates truss response using Finite elements where 2-D planar elements were used to calculate the response of the truss. Parameters for the connection strength are derived from the joint tests. Moment stiffness and axial stiffness values of the connections were determined. Combined load tests showed that there is indeed a measurable effect on joint stiffness and capacity due to combined loads, some of which actually contribute to the stiffness, but also some which are detrimental. There is good correlation between the truss test results and the FE model using semi-rigid joints. However, results of the simpler non-linear frame analysis, did not compare so well, but nevertheless exhibited fundamental characteristics of the truss.

Le développement des structures en bois en Génie Civil demande aujourd’hui de proposer aux gestionnaires d’ouvrages des outils de diagnostic et de monitoring pour suivre l’évolution des pathologies (flèches excessives, fissures, attaques biologiques, etc.) mais également pour contrôler l’humidité interne dans les éléments. Dans ce dernier contexte, le travail développé dans cette thèse concerne le développement d’un outil de caractérisation du champ hydrique dans des sections transversales d’éléments structuraux en bois. La méthode étudiée couple une mesure de résistivité, composée d’une tête de mesure (résistivimètre) associée à un grand nombre de sondes raccordées à un système multiplexé, et d’une méthode inverse implémentée dans un code aux éléments finis. Dans une première partie, il est étudié les techniques de caractérisation des propriétés de diffusion dans le matériau caractérisé par une orthotropie et un comportement non linéaire exploitant des mesures d’humidité moyenne (méthode gravitométrique) et des profils spatiaux par mesures gammadensimétriques. Il est montré que le couplage des deux mesures permet d’obtenir en finalité des propriétés intrinsèques rendant ainsi la méthode de caractérisation fiable et robuste. La seconde partie présente le développement d’un ensemble expérimental dans le but d’obtenir une cartographie 1D et 2D du champ hydrique dans une section transversale. La technique repose sur la généralisation des méthodes résistives multiplexées utilisées en géophysique dans l’étude des sols stratifiés à des géométries finies à 2 dimensions. L’algorithme employé est basé sur le couplage de mesures de résistivité multiplexées et d’une analyse inverse implémentée dans un code aux éléments finis. La solution 1D permet d’obtenir des profils spatiaux pouvant remplacer les mesures gammadensimétriques. Les profils 2D permettent, pour une section donnée, d’estimer le champ d’humidité interne en tout point et de proposer ainsi un suivi dans le temps des profils hydriques. / In civil engineering constructions, the development of timber structures requires today to managers works some diagnostic tools and monitoring systems to monitor pathologies (excessive deflections, cracks, biological attack, etc.) but also to control moisture content in the element sections. In the last context, the proposed work in this PhD thesis is the development of a tool for characterization of the moisture content map in the cross sections of structural elements. Studied method is based on the resistivity measuring, comprising a measuring head (resistivity meter) associated with many connected probes in a multiplexed system, and an inverse method implemented in a finite element software. In the first part, it is studied the techniques of characterization of diffusion properties in wood samples characterized by orthotropic and nonlinear behaviors according to average moisture content measurements (gravimetric method) and spatial profiles gamma densitometer measures. It is shown that the coupling of the two measurements provides the intrinsic properties with more reliability and more robustness. The second part deals with the development of an experimental protocol in order to achieve 1D and 2D mapping of the moisture content field in a cross section. The technique is based on the generalization of multiplexed resistivity geophysical methods used in the study of stratified soils with 2-dimensional geometries. The algorithm is based on the coupling between the resistivity measurements and an inverse multiplexed analysis implemented in a finite element code. The 1D solution provides spatial profiles which can replace gamma densitometer measures. For a selected section, 2D profiles allow estimating the moisture content field at any point and thus provide a time tracking of moisture profiles