Comportement mécanique de planchers diaphragmes en bois : semi-rigidité et résistance pour une situation sismique

Abstract : In timber structures as other, floors play an important role in the overall behaviour of a building subjected to seismic loading. In addition to the vertical forces, these floors transfer horizontal forces to the shear walls (diaphragm function). For this function, the floor can be considered as a short beam placed horizontally and supported by semi-rigid supports (shear walls). Therefore, the force distribution on the shear walls is directly related to the in-plane stiffness ratio between floors and shear walls.Traditional wooden floors are usually composed by joists framing (joist, struts, chords beams) and a surface made by juxtaposed panels. The panel-joist framing connection is usually made by nails. Size of the floors elements is often driven by the vertical loads, thus mechanical properties in the plane are rarely checked.The in-plane behaviour of timber floor is poorly studied in the literature. This thesis studies this behaviour using three approaches: analytical, numerical (FEM) and experimental. The analytical approach is based on that used in North American codes of seismic design. Numerical models take into account the actual geometry of the timber diaphragms and nonlinear effects (material and geometric). Two types of numerical models are proposed: "detailed" and "simplified". The detailed model, based on beams and shell elements, allows studying the distribution of internal stresses in the floor. The simplified model uses beams and bar elements. It allows carrying out sensitivity analysis and can be used to study complex geometries of floors.An experimental campaign is conducted on timber floors. Two floors (2,4 x7,2m2), in blocked or unblocked configuration, are tested in bending in their plane. Displacement transducers, inclinometers and a camera measuring system are used for monitoring the behaviour of floors at global and local levels. The experimental observations show a highly nonlinear behaviour with a significant influence of struts on the stiffness and strength. Panels failure due to bending and compression in the corners were observed. The comparison between experimental and numerical results allows validating the numerical models. These models show a significant participation of the panels-joist framing connection on the global and local mechanical behaviour of floors.The simplified model is used to conduct a sensitivity analysis of floors with hoppers. Thirteen floors configurations are analyzed to identify the most unfavourable configurations of hoppers position. Furthermore, the analytical model represents well the linear phase of floors behaviour. The numerical and experimental results obtained provide a good basis to expand the scope of the analytical model.
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Sebastian Fuentes. Comportement mécanique de planchers diaphragmes en bois : semi-rigidité et résistance pour une situation sismique. Génie civil. Université Blaise Pascal - Clermont-Ferrand II, 2013. Français. ⟨NNT : 2013CLF22360⟩. ⟨tel-01935761⟩



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