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Re: 1991 NDS Values for Lumber

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>From the desk of Joe Otto wrote:
> 
> Neil:
> 
> My understanding of the code leads to the following:
> 
> Lets use the example of a 24' long 4x14 DF#1 purlin.  The allowable moment
> (neglecting repetitive use and noting that the moisture content will not
> exceed 19%) are as follows:
> 
> The "old" values
> S(fb)(Cf)(LDF) = 102.41in^3(1500 psi)(12/13.25)^1/9(1.25)(1
> kip/1000#)(1ft./12in.) = 15.84 kip-ft.
> 
> The 1991 NDS leads to the following:
> S(fb)(Cf)(LDF) = 102.41in^3(1000psi)(1.0)(1.25)(1/12000)= 10.67 kip-ft.
> 
> Are these the design moments that should be used?
> 
> Joe
> 
That will work for that particular member, however don't forget the
shape factor for members with a "d" less than 12".  It will greatly
increase the strength of the smaller sizes.  Also you should make note
of the load duration factor, but that probably goes without saying.

Enjoy, 	Jake Watson E.I.T.
	Salt Lake City, UT