Wood's structural properties derive from fibers aligned along the tree's length, contributing significantly to its mechanical strength. Wood exhibits up to twenty times greater tensile strength along these fibers compared to across them, and generally shows better performance under compression than tension. The length of fibers varies, with hardwoods having fibers around one twenty-fifth inch long and softwoods ranging from one-eighth to one-third inch.
The strength characteristics of wood are evaluated through laboratory tests assessing its behavior under bending, shear, tension, and compression forces. This testing is crucial for understanding how wood will handle various stresses in practical applications.
Lumber, a primary form of processed wood, is categorized based on size into boards, dimension lumber, and timbers. Boards are defined by a thickness of less than two inches, including sizes like one by two, or one by six. Dimension lumber ranges from two to four inches in thickness and is typically sold in lengths from eight to twenty-four feet, including sizes such as two by four, or three by ten. Timbers, the largest category, start at five inches thick with examples like five by ten or six by six, used in more substantial structural applications. Nominal sizes in lumber refer to dimensions before finishing, while actual sizes are the true measurements after processing. For example, a 2 by 4 inches is actually 1.5 by 3.5 inches.
These categories of lumber are tailored for specific uses in construction, from general buildings to specific, load-bearing structures, ensuring versatility and reliability in a wide range of building projects.
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.
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