WOOD - Materials for Civil and Construction Engineers - page 418

Volume

■

Flat use

■

Repetitive member

■

Curvature

■

Form

■

Column stability

■

Shear stress

■

Bearing area

■

In addition, sustained loads will cause wood to creep. In design appli-
cations, this means that the wood can carry higher stresses of short time
durations than the same wood element can carry for a long-term applica-
tion. Generally, a load duration of 10 years is used for design. Typical load
duration factors that would be applied to the values in Tables 10.3 and
10.4 (except for compression perpendicular to the grain) are shown in
Figure 10.13. For example, if a floor joint is designed for a temporary stage
that is used only for a one-day presentation, the allowable bending fiber
stress can be increased by 33 percent over the allowable stress for a normal
application.

10.11 Organisms that Degrade Wood

Wood can experience degradation due to attack of fungi, bacteria, insects, or
marine organisms.

2.0

1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0

10 minutes
7 days
2 months

1
second

1
day

1
year

10
years

Permanent

Duration of maximum load

FIGURE 10.13 Adjustment factors for load duration working-stress for
wood design based on 10-year nominal duration. Reprinted with permission
of American Forest and Paper Association (2005.)