Review on the Bending Strength of Wood and Influencing Factors

Abstract

The bending strength values of clearwood specimens are examined in the range of flexural fracture. The values should be higher under centre loading than under third-point loading due to the size effect and decrease with increasing span length. The equations used for the size effect are criticised. The maximu m tensile stress in the beams is lower for centre loading and higher for third-point loading, than calculated according to the classical beam theory. This requires a first correction of the simp le size effect to a size/stress effect. So metimes the measured values show a trend, contrary to the size/stress effect, caused by deformation at the load points. These deformations depend on the loading configuration, the orientation of the annual rings, and the co mpression strength perpendicular to grain. The evaluation of the measured values can lead to incorrect conclusions using just the equations of the simp le size effect.