Anisotropy Influence in Obtaining Stiffness Property in Bending of Brazilian Wood Species

Abstract

The design of timber structures, and other materials, must follow the procedures and methods of calculation of normative standards. Some normative documents in the design of timber structures adopt quite simple arithmetical relationships to relate wood properties in order to make it simple and quick evaluation of the behavior of structural elements, as is the specific case of Brazilian standard ABNT NBR 7190:1997, establishing a single relation for the shear (G) and the longitudinal (E) modulus of elasticity [E=G/20], which implies taking statistical equivalence to the values of the elastic moduli in the longitudinal-radial (G<SUB>LR</SUB>) and longitudinal-tangential (G<SUB>LT</SUB>) directions, which are important properties in relation to the requirements of structural projects. In this context, this study aimed to investigate, with the aid of four and three points static bending tests performed on the of dicotyledonous wood species grown in Brazil, the determination of the values of E<SUB>LR</SUB>, E<SUB>LT</SUB>, G<SUB>LR</SUB> and G<SUB>LT</SUB> to confirm the possibility of its equivalence (E<SUB>LR</SUB> and E<SUB>LT</SUB>, G<SUB>LR</SUB> and G<SUB>LT</SUB>), and for establishing correlations among them. The results of the hypothesis testing between the shear and longitudinal modulus of elasticity exhibited equivalent by species and simultaneously for all species, and the results of the linear regression model showed not possible to estimate the shear modulus of elasticity with knowledge of the longitudinal modulus of elasticity, and the optimal coefficient found by least squares method to the relation between the modulus of elasticity was equal to 35 (E=G/35), suggesting the need for an adjustment of the coefficient for this scale more safe wooden structures.