Prediction of Strength and Elasticity in Oak Beams on the Basis of External Wood Characteristics

Abstract

The purpose of the study was to search external features of timber useful for predicting modulus of rupture (MOR) and modulus of elasticity (MOE), both in axial direction bending, valid for a wide range of beam qualities. For the study, 23 European oaks (Quercus robur L.) were felled in northwestern Spain, where most of the oak stands in the country are located. The trees were sawn and a sample of quarter-sawn planks was selected. Planed and edged specimens (5×10×200 cm) were tested to obtain MOR, MOE, apparent density, wood moisture content, percentage of sapwood, ring width, slope of grain and size and position (faces, upper and lower edge, heads) of external defects. The MOR was correlated with the maximum face and edge knot diameter. However, the correlations were not high enough to justify construction of a predictive model of mechanical behavior on the basis of maximum knot size in the piece. The MOE was correlated with the size of knots and wane. Presence of sapwood did not exhibit significant influence on strength performance. Homogeneity in ring width was negatively related to MOR and mainly to MOE. Subject headings: Bending; Mechanical properties; Stiffness; Wood beams; Wood structures.