Abstract

Using of timber in civil engineering is increasing at the moment. Main timber elements are used for main supporting structures, typically for buildings, roofs, footbridges or towers. This work studies unique timber trusses as a supporting roof structure of spatial timber building. Timber trusses are used as roof supporting construction for objects with open inside space, especially halls or office buildings. This paper resolved critical joint in roof construction which is created by four timber trusses. The FEM model monitored strain changes in critical places of resolved joint.

Abstract

Abstract

Abstract

Some of the most frequently observed phenomena in structural materials are creep and relaxation. Both are associated with time-dependent behavior and dissipative rheological variables. In the case of wood, long-term creep can produce excessive deformation and instability problems by magnifying short-term deflections. Also, wood presents changes in its mechanical properties due to its hygroscopy, so that moisture appears as an important parameter to be considered. A priori, it is known that the moisture content in wood cells and the angle of microfibrils are parameters that directly affect the overall cell stiffness. With this information, material physics hypotheses can be elaborated to develop a constitutive model in large deformations to predict phenomena such as creep and relaxation in the medium and/or long term. The microstructure of the cell wall can be represented through a model of fiber-reinforced composite material originally developed for biomaterials such as arteries and fibrous tissues. Where the anisotropic character is conferred by the distribution of the fibers within the isotropic matrix of the material. This work aims to adapt these models to represent the mechanical behavior of the wood cell with faithful representation of its microstructure. FEniCS is used for the numerical implementation of the material. In this paper the validations, current status, conclusions, and perspectives of this research are presented.

Abstract

Abstract

Abstract

Several methods to determine in-plane shear properties of anisotropic materials (i.e. fiber reinforced composite materials and natural wood) based on flexural loading have been proposed. One of those methods is the off-axis bending test that considers unidirectional composite materials subject to three-point bending (3-PB) loading. As a result of the anisotropic behaviour, unidirectional off-axis laminates subjected to flexure present a bending–twisting coupling that may cause, in the case of three-point bending loading, a lift-off of the specimen on the fixture supports. Such specimen lift-off has been considered one of the critical features to be considered on the mentioned experimental method. Besides, geometrical parameters and material elastic constants (i.e. longitudinal, transversal, and shear elastic moduli) influence the validity to use this method for characterizing in-plane shear properties. On that sense, an analytical approach for studying the material conditions for which the application of the off-axis 3-PB test is adequate to characterize natural wood is presented in this work. The condition of small displacements and the condition of lift-off between the specimen and the fixture supports have been taken into account. Some theoretical ideas regarding stress and displacement fields are also presented. The in-plane shear characterization has been performed on two natural wood species: Norway spruce (Picea abies) and beech (Fagus sylvatica). Test conditions for the off-axis 3-PB experimental bending test, in order to ensure its applicability, are presented.