Recommendations

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

K=0.64(E/f_c)^1/2

The range of the slenderness ratio and the allowable stress assigned to each category are next.

Short column

L/d<=11
f=f_c

Intermediate column

11<=K
f=f_c[1-0.34(L/Kd)⁴]

Long column
L/d>K
f=0.274E/(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:

f=0.30E/(L /d)²

but f <=f_c

The notational system for the preceding equations is

P= allowable load
A= sectional area
L= unbraced length
d= smaller dimension of rectangular section
E= modulus of elasticity
f_c= allowable compressive stress parallel to grain in short column of given species
f =allowable compressive stress parallel to grain in given column