The effect of wanes on the bending strength of solid timber beams

Abstract

A theoretical analysis is conducted to determine the effect of wanes on the bearing capacity of timber in light of the reduction they entail in cross-sectional area compared to fully rectangular sections. The concomitant loss of bending strength is likewise evaluated. Parallel tests are run on 84 samples —51 with wanes— of large section, Scotch (Pinus sylvestris L.) and Corsican (Pinus pinaster Ait.) pine beams taken from old buildings. The bending strength, modulus of elasticity and density are found in accordance with European standard EN 408. The mechanical properties of the specimens with and without wanes are found to be very similar, and no statistically significant differences are recorded. The effect of the decline in section may be offset by greater continuity of surface fibers and the section shape effect. One practical consequence of this finding is that (within certain limits) wanes may be disregarded when grading large section timber beams in existing structures, where this flaw is very common; this in turn would reduce the high percentage of rejected beams imposed by the present visual grading standards.

Keywords

• timber
• structures
• defects
• wanes
• visual grading