CIVIL ENGINEERING FORMULAS

162 CHAPTER SIX

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

RECOMMENDATIONS OF THE FOREST PRODUCTS
LABORATORY

TheWood Handbookgives 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
Kdenote a parameter defined by the equation

(6.11)

The range of the slenderness ratio and the allowable stress assigned to each cat-
egory are next.
Short column,

(6.12)

Intermediate column,

(6.13)

Long column,

(6.14)

The maximum L/dratio is set at 50.
The National Design Specification covers the design of solid columns. The
allowable stress in a rectangular section is as follows:

(6.15)

The notational system for the preceding equations is

Pallowable load

Asectional area

Lunbraced length

f

0.30E

(L/d)^2

but f fc

L

d

K f

0.274E

(L /d)^2

11 

L

d

K ffc 1 

1

3 

L/d

K 

4



L

d

 11 ffc

K0.64

E

fc

1/2