Effect of size on bending strength of wood members

The report discusses a size-strength relationship developed for the bending strength of wood beams by using a statistical theory of strength of materials. The results show that the modulus of rupture depends on the length and depth of the beam and on method of loading, but is independent of beam width. theoretical results compare favorably with observed data from clear, straight-grained, Douglas fir beams having sizes ranging from 1 inch deep by 14 inches long to 31-1/2 inches deep by 48 feet wide.