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Wood Stress Increase for Wind

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Title: Wood Stress Increase for Wind


I'll attempt to answer your questions. I'm confident about #1. Hoping you'll get other opinions on #2 and #3 below:

1) yes, the 1.6 load duration factor can be used to adjust wood design values (except E and Fcperp) for members and connections resisting wind loads calculated per IBC 1605.3.1 or 1605.3.2. If you want more background, check the NDS Commentary, section at the following link:

2) It seems, you only need to use the 1.3 factor IF you want to use the alternate load combinations of 1605.3.2 AND the simplified wind procedures of IBC 1609.6.

3) Again, it seems IF you are using the alternate load combinations AND the simplified wind load method, 1.3 would apply whether you are calculating C&C or MWFRS. I didn't see an exception in 1609.6 to the contrary.



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.


To: seaint(--nospam--at)
Subject: Wood Stress Increase for Wind
From: richard lewis <rlewistx(--nospam--at)>
I'm a little confused on what is permitted for the duration of load for
wind using the newer IBC and ASCE. They both state that for allowable
stress design the allowable stress can't be increased for wind.
Equations in Section 1605.3.2 can be used for alternate load cases where
the stress may be increased, provided the wind is increased by a factor
of 1.3. Section 1605.3.1.1 states that for wood the duration of load
factors can be used for design provided it is designed in accordance with
Chapter 23 - wood chapter. I looked through chapter 23 for some general
information regarding the duration of load with the load combinations and
didn't find anything.
Can the 1.6 duration of load factor be used for wind design with wood?
If so, does the wind value have to be increased by 1.3? Also, if the
design is based on components and cladding, does the wind value need to
be increased for this as well? The IBC tends to indicate the increase is
only needed for MWFRS if it is done by the simplified method. Components
and cladding design is not limited to simplified building analysis.
One reason I ask is to know what Simpson Anchor design values I can use.

I can't wait until all the design specifications catch up to one another.