3.4 : 木料的结构特性和尺寸

Wood fibers align along the tree's length, giving it up to twenty times higher tensile strength along the fibers than across them. Wood is also generally stronger in compression than in tension.

Hardwoods have fibers around one twenty-fifth inch long, while softwood fibers range from one-eighth to one-third inch.

The strength properties of wood are determined by laboratory tests such as bending, shearing, tension, and compression.

Usual lumber products include boards, dimension lumber, and timber.

Boards are less than two inches in their smallest nominal dimension. For example, sizes like one by two, one by six, or five-quarters by four are categorized as boards.

Dimension lumber typically measures between two to four inches in its smallest dimension.

This includes sizes such as two by four, three by ten, and four by four, available in increments of two feet in length, ranging from eight to sixteen feet and up to twenty-four feet in some cases.

Timbers have a minimal nominal dimension of five inches or more, such as five by ten or six by six.