Influence of loading face on the modulus of elasticity in static bending of tropical wood

Abstract

Ehe modulus of elasticity is a fundamental parameter in the structural design of timber elements, as it directly controls displacement response and serviceability performance. The methodology established by NBR 7190-3:2022 and by other international standards for determining this property is based on static bending tests performed on small clear prismatic specimens. However, these standards do not explicitly define which longitudinal face of the specimen should be subjected to loading, which may introduce an additional source of variability in the measured results. Considering the anisotropic behavior and inherent heterogeneity of wood, this study evaluated the existence of significant variations in the modulus of elasticity obtained from the four longitudinal faces of specimens from twelve tropical hardwood species. Statistical analyses based on paired t-tests at a 95% confidence level confirmed significant differences, demonstrating that the loading face influences the estimated stiffness. The least squares method was applied to quantify the variability between the maximum and minimum modulus values obtained for each specimen. An average variation of approximately 4% was observed among the different loading face configurations. Based on these findings, a correction coefficient (γ = 0.96) is proposed to adjust modulus of elasticity values derived from bending tests, enhancing measurement representativeness and reliability for structural applications.