CIVIL ENGINEERING FORMULAS

CHAPTER 6

157

TIMBER

ENGINEERING

FORMULAS

GRADING OF LUMBER

Stress-grade lumber consists of three classifications:

1.Beams and stringers. Lumber of rectangular cross section, 5 in (127 mm) or
more thick and 8 in (203 mm) or more wide, graded with respect to its strength
in bending when loaded on the narrow face.

2.Joists and planks. Lumber of rectangular cross section, 2 in (50.8 mm) to,
but not including, 5 in (127 mm) thick and 4 in (102 mm) or more wide,
graded with respect to its strength in bendingwhen loaded either on the nar-
row face as a joist or on the wide face as a plank.

3.Posts and timbers. Lumber of square, or approximatelysquare, cross section
5 5 in (127 by 127 mm), or larger,graded primarily for use as posts or
columns carrying longitudinal load, but adapted for miscellaneous uses in
which the strength in bendingis not especially important.

Allowable unit stresses apply only for loading for which lumber is graded.

SIZE OF LUMBER

Lumber is usually designated by a nominal size. The size of unfinished lumber
is the same as the nominal size, but thedimensions of dressed or finished lum-
ber are from to in(9.5 to 12.7 mm) smaller. Properties of a few selected
standardlumber sizes, along with the formulas for these properties, are shown
in Table 6.1.

(^1) 
2
(^3) 
8