Mechanical Behaviour of Wood Beams with Grain Orientation

Abstract

Wood is a material with a mechanical behavior that is dependent on the direction of its fibers. Due to its internal structure, wood is generally treated as linear orthotropic, with the material directions (longitudinal, radial and tangential) ideally coincident with the longitudinal and transverse directions of a coordinate system associated with a structural member. Such coincidence does not occur in the field of lumber production. In wood beams, the fiber orientations are typically not aligned with the longitudinal direction from 5° to 15°. This affects the wood mechanical properties and requires a transformation of coordinates of the elastic coefficients to adjust them to the adopted model for structural analysis. Thus, additional terms appear in the constitutive relationship transforming wood as an anisotropic material. By introducing these coefficients on the elastic model, a study of the stresses in wood beams, constituted by a Brazilian species named Goupia glabra, was developed by applying an analytical method and a program of finite elements. Numerical examples confirm that the fiber orientation, even for small angles, has a large influence on the mechanical behavior of wood beams.