Evaluation of wood modulus of rupture and modulus of elasticity in the radial and tangential directions in bending and reliability analysis

Abstract

Structural lumber is designed according to technical standards, in which the material properties are determined through standardized tests and their average values are commonly adopted. To improve knowledge of the mechanical properties of wood, this work seeks to evaluate the modulus of rupture and the modulus of elasticity, considering the radial and tangential loading directions in bending. The bending test procedure followed the American standard ASTM D143, employing small clear specimens of sugar maple species (Acer saccharinum). This study also addresses the influence of wood density on the values obtained for these moduli. From the experimental results, it is noted a statistical difference between the moduli, with the highest values for both in the radial direction. In addition, the density affects more significantly the modulus of rupture than the modulus of elasticity. On the basis of this investigation, the results of the moduli of rupture and elasticity and their correlations are used, through the decomposition of singular values, to generate new values in order to analyze the effect of the two loading directions on the structural safety estimation from the reliability indices for structures under bending via Monte Carlo simulations. Such indices became significantly higher for specimens loaded in the radial direction when compared to the tangential one, based on the mean load. Finally, to make the safety between the moduli of rupture and elasticity in both loading directions in bending compatible, a modification factor of 1.06 related to maximum loads is proposed.