Note Footnote 7: — Chapter II

Strength also includes the ability to resist shear. This is called "shearing strength." It is a measure of the adhesion of one part of the wood to an adjoining part. Shearing is what takes place when the portion of wood beyond a mortise near the end of a timber, A B C D, Fig. 43, is forced out by the tenon. In this case it would be shearing along the grain, sometimes called detrusion. The resistance of the portion A B C D, i.e., its power of adhesion to the wood adjacent to it on both sides, is its shearing strength. If the mortised piece were forced downward until it broke off the tenon at the shoulder, that would be shearing across the grain. The shearing resistance either with or across the grain is small compared with tension and compression. Green wood shears much more easily than dry, because moisture softens the wood and this reduces the adhesion of the fibers to each other.7