Page 228 - Civil Engineering Formulas

162 CHAPTER SIX

2
where c allowable unit stress at angle to grain, lb/in (MPa)
2
c allowable unit stress parallel to grain, lb/in (MPa)
2
c allowable unit stress perpendicular to grain, lb/in (MPa)
angle between direction of load and direction of grain

RECOMMENDATIONS OF THE FOREST PRODUCTS
LABORATORY

The Wood Handbook gives advice on the design of solid wood columns. (Wood
Handbook, USDA Forest Products Laboratory, Madison, Wisc., 1999.)
Columns are divided into three categories, short, intermediate, and long. Let
K denote a parameter defined by the equation
1/2
E
K 0.64 (6.11)
f c
The range of the slenderness ratio and the allowable stress assigned to each cat-
egory are next.
Short column,
L
11 f f c (6.12)
d
Intermediate column,
L K f f c 1 L/d 4
11 1 (6.13)
d 3 K

Long column,
L 0.274E
K f (6.14)
d (L /d) 2
The maximum L/d ratio is set at 50.
The National Design Specification covers the design of solid columns. The
allowable stress in a rectangular section is as follows:
0.30E
f but f f c (6.15)
(L/d) 2
The notational system for the preceding equations is

P allowable load
A sectional area
L unbraced length