Knee (construction)

Wood is a highly anisotropic material (its strength varies considerably with the direction of applied force, i.e., parallel, radial, or tangential to the grain).

To avoid this issue knees requiring sharper curves are made using methods which ensure that the wood grain and direction of load are closely aligned.

This can be achieved by steam bending, laminating, or selecting a natural crook with matching grain - a "grown knee".

Steam-bending is a time-honored method for shaping boat frames, but it does weaken the wood slightly, it can leave residual stresses which may cause breakage or spring-back over time, and it is limited in the degree of bend which it can achieve, particularly for thick members.

This provides a fairly reliable source of approximately 90 degree crooks which may be impossible to find in other portions of the tree.

Commonly used in shipbuilding known as ship's knee for their advantage of reducing the encroachment into the usable space of the structure since there is no spandrel.

Due to tradition, ease of workability, strength and durability characteristics, some species of wood are particularly prized for making knees.