La regularidad en la anchura de anillos de crecimiento y su empleo en la clasificación visual de la madera para su asignación al sistema Europeo de clases resistentes

The homogeneity of wood growth ring width is associated with greater rigidity and mechanical strength of the material. Therefore, understanding ring width homogeneity would be useful for visually grading sawn wood for structural applications. However, the effect of homogeneity on mechanical performance of wood has not been quantified. In this study, the dispersion of the ring width was analyzed to assess its predictive value for elasticity and axial bending strength in Quercus robur (european oak) wood beams. To carry out the study, 26 adult oak trees were felled in Galicia (northwestern Spain). The stems obtained were cut and sawn to produce planks, which were air-dried and subsequently planned to produce beams with target dimensions 2000 mm × 100 mm × 50 mm. For a sample of 52 of these beams, we measured the axial bending strength, the elastic modulus in axial bending, the wood density and moisture content, as well as the percentage of sapwood and the width of each growth ring in the cross section. The descriptive variables of the ring homogeneity, calculated using data from all rings in each beam (standard deviation, variance, interquartile range), were more closely related to mechanical properties. Beams with more homogeneous rings exhibited significantly higher elastic modulus and axial bending strength, with the strongest correlation observed between ring width variance and axial bending elastic modulus (R = -0,41**). However, the correlations observed do not justify developing a predictive model for elasticity or mechanical strength based solely on ring width homogeneity, although me-chanical behavior is significantly influenced by ring homogeneity. Consequently, this characteristic could be incorporated into visual strength grading standards for oak wood