Building Design and Construction Handbook - Merritt - Ventech!

10.14 SECTION TEN
TABLE 10.6 Wet Service Factors C M
Design
value
10.5.3 Temperature Factor
C M for sawn
lumber*
TABLE 10.7 Temperature Factors C t
C M for glulam
timber†
C M for
timber
F b 0.85‡ 0.80 1.0
F t 1.0 0.80 1.0
F V 0.97 0.875 1.0
F e� 0.67 0.53 0.67
F c 0.80§ 0.73 0.91
E 0.90 0.833 1.00
* For use where moisture content in service exceeds 19%.
† For use where moisture content in service exceeds 16%.
‡ C M � 1.0 when F bC F � 1150 psi.
§ C M � 1.0 when F cC F � 750 psi.
Design values apply to members used in ordinary temperature ranges. (Occasional
heating to 150�F is permissible.) Strength properties of wood, however, increase
when it is cooled below normal temperatures and decrease when it is heated. Members
heated in use to temperatures up to 150�F return essentially to original strength
when cooled. Prolonged exposure to temperatures above 150�F, however, may result
in permanent loss of strength. Design values for structural members that will experience
sustained exposure to elevated temperatures up to 150�F should be multiplied
by the appropriate temperature factor C t listed in Table 10.7.
10.5.4 Size Factor
For visually graded dimension lumber, design values F b, F t, and F c published in
the supplement to NDS for all species and species combinations, except southern
pine should be multiplied by the appropriate size factor C F given in Table 10.8 to
account for the effects of member size. This factor and the factors used to develop
size-specific values for southern pine are based on the adjustment equation given
in ASTM D1990. These factors, based on in-grade test data, account for differences
in F b, F t, and F c related to width and in F b and F t related to length (test span).
For visually graded timbers (5 � 5 in or larger), when the depth d of a stringer,
beam, post, or timber exceeds 12 in, the design value for bending for all species
should be adjusted by the size factor
Design values and
in-service moisture
conditions T � 100�F 100�F � T � 125�F 125�F � T � 150�F
F t and E, wet or dry 1.0 0.9 0.9
F b, F V, F c, and F c�
Dry 1.0 0.8 0.7
Wet 1.0 0.7 0.5