Page 524 - Forensic Structural Engineering Handbook

14.14 MATERIAL-SPECIFIC FORENSIC ANALYSES

TABLE 14.2 Temperature Factor C
t
C t
In-service
Design moisture
values conditions T ≤ 100°F 100°F < T < 125°F 125°F < T < 150°F
E t . E Wet or dry 1.0 0.9 0.9
F . F ’ Dry 1.0 0.8 0.7
b v
F ’ F ⊥ Wet 1.0 0.7 0.5
c
c
Source: American Forest & Paper Association, Washington, D.C.
TABLE 14.3 Frequently Used Load Duration Factors (ASD only)

Load duration C D Typical design loads
Permanent 0.9 Dead load
10 years 1.0 Occupancy live load
2 months 1.15 Snow load
7 days 1.25 Roof live load
1 day 1.33 Wind/seismic load
10 min 1.6 Wind load
Instantaneous 2.0 Impact load

TABLE 14.4 Time Effect Factor, λ (LRFD only)
Load combination l
1.4(D + F) 0.6
1.2(D + F) + 1.6(H) + 0.5(L or S or R) 0.6
r
1.2(D + F) + 1.6(L + H) + 0.5(L or S or R) 0.7 when L is from storage
r
0.8 when L is from occupancy
1.25 when L is from impact
1.2D + 1.6(L or S or R) + (L or 0.8W) 0.8
r
1.2D + 1.6W + L + 0.5(L or S or R) 1.0
r
1.2D + 1.0E + L + 0.2S 1.0
0.9D + 1.6W + 1.6H 1.0
0.9D + 1.0E + 1.6H 1.0

important consideration in forensic analysis of timber that is not mentioned in the previous
allowable stress NDS nor the current NDS that is basically an allowable stress document
3
with adjustment factors in Appendix N for use as LRFD. Further discussion of this effect
is included in the “Accumulation of Fiber Damage” section.
The load duration is the accumulated time the design load is applied during the life of
the structure. For example, the usual duration factor for snow loading is 1.15 for a 2-month
duration. This does not mean 2 months of snow loading per year or 2 months of continuous
snow loading, but rather 2 months of design snow loading during the life of the structure.
If the design snow load could reasonably be applied for more than 2 months, such as at a