Influenceof the angle between applied stressand wood grain direction on the module of elasticity

Abstract

The Brazilian Code, NBR 7190 - Design of Timber Structures, foresees the correction of the strength to the normal tensions when the angle between the effort and the direction of the fibers (a) is larger than 6^o and recommends the application of Hankinson's expression to the calculated values, but is remiss about the module of elasticity correction. This work aimed to search in the literature other expressions to represent the variation of the module of elasticity with the angle and to verify the validity of these expressions in mean values. A sample comprised of 12 boards was used. From each board compression test blocks with different grain inclinations were taken and tested according the NBR 7190, providing the modules of elasticity for different angles. From the results of one board the module of elasticity variation, with the a angle, was obtained. After setting an inclination it was possible to obtain (according the NBR 7190) the effective stiffness (average module of elasticity) for the fixed inclination. Based on these mean values the variation of the effective stiffness with the a angle was obtained. Four models (Hankinson, Sins, Karlsen and Keylwerth) were evaluated, using the pairing and the residues tests.In both cases the Keylwerth model was the most efficient to represent the phenomenon.