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I just realized I blew it on the original post (the analysis is OK).  Size
factor for 2x10's is 1.1 not 1.2.


----- Original Message -----
From: "Conrad Guymon" <conrad(--nospam--at)>
To: <seaint(--nospam--at)>
Sent: Wednesday, May 30, 2001 11:51 AM
Subject: Change in Dimension Lumber Design Values

> I have been asked to evaluate a building constructed in 1963.  Design
> drawings indicate that Construction Grade D.F. 2x10's are to be used with
> allowable Fb of 1500 psi for the roof framing.  Current code accepted
> (1997 UBC) for Const. Grade D.F. 2x10's are Fb*Csubf=1000*1.2=1200 psi.
> The structure was designed for 30 psf snow,  and the current snow load
> requirement is 50 psf, (which is reasonable for the area).  I can show
> the structure works using the original design values, but not the current
> ones.  The building appears to be performing adequately, but I need
> something to justify the use of the higher original allowable stresses.
> I've been through the changes to the 1991 NDS, but the literature I can
> isn't much help.
> Does anyone have an explanation (with documentation) for the change in
> allowable stresses?
> Thanks
> Conrad Guymon, P.E.

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