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Adjustment Factors Cd for timber column

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In addition to the points that have been made:


1)  As with any material, all load combinations have to be evaluated to determine which one controls. So, while it seldom controls for wood, dead load acting alone would also have to be checked with a load duration factor of 0.9. I know that the example problem to which you are referring is asking for the largest D+L permitted on the column, but I wanted to make sure we cover all the bases.

2)  The load duration factor is applied to the appropriate design values, not the load combination. The reason is because load duration factors are not applied to modulus of elasticity or to compression perpendicular to grain.


There’s more discussion about this subject in Appendix B of the NDS®.


Hope this helps.




John "Buddy" Showalter, P.E.
Director, Technical Media
AF&PA/American Wood Council
1111 19th Street, NW, Suite 800
Washington, DC 20036
P: 202-463-2769
F: 202-463-2791

The American Wood Council (AWC) is the wood products division of the American Forest & Paper Association (AF&PA). AWC develops internationally recognized standards for wood design and construction. Its efforts with building codes and standards, engineering and research, and technology transfer ensure proper application for engineered and traditional wood products.

The guidance provided herein is not a formal interpretation of any AF&PA standard.  Interpretations of AF&PA standards are only available through a formal process outlined in AF&PA's standards development procedures.



From: ken ng [mailto:zy7up(--nospam--at)]

Sent: Thursday, February 05, 2009 09:08

To: seaint(--nospam--at)

Subject: Adjustment Factors Cd for timber column


I'm looking at 2005 Examples Structural Wood Design Problem  #2.  Column ha=

s D+S, and the example used Cd =3D 1.15 which is Snow load and neglected Cd=

=3D0.9 for Dead load.

Does anyone know why Cd=3D0.9 was not apply?