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Re: Change in Dimension Lumber Design Va

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4-inch (nominal) and smaller were sized 3/8" off the nominal size.

6-inch (nominal) and larger were sized 1/2" off the nominal size.

Some rough sawn actual dimensions were the same as the nominal dimensions.  
Others could be different.  I have seen 2 X 6 (nom.) rough sawn 1-3/4" X 6" 
(actual) as well as 2" X 6" (actual).


A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Conrad Guymon wrote:

Would 2x8's also be 1-5/8 x 7-1/2?

----- Original Message -----
From: "Roger Turk" <73527.1356(--nospam--at)>
To: "SEAOC Listservice" <seaint(--nospam--at)>
Sent: Wednesday, May 30, 2001 3:44 PM
Subject: Change in Dimension Lumber Design Values

> I wrote:
> . > Pre-1970 sizes were also different, with 2-inch nominal being 1-5/8
> . > inches.  2 X 10's were 1-5/8" X 9-1/2" (IIRC - I'll check in about an
> . > hour.)
> Confirmed.  The properties are:
>    A     = 15.44 in^2
>    I     = 116.1 in^4
>    S     = 35.82 in^3
> Also, to the best of my knowledge, the new lumber stresses had nothing to
> with new growth/old growth wood.  In the late 1970's, tension tests on
> full-size, in-grade lumber indicated a significant reduction (40 - 60
> percent) in allowable tension stress than the small, clear specimens
> indicated.  (ICBO came out with an emergency code change in 1979, reducing
> the allowable tension stress 60 percent.)  I believe that it was this
> discovery that caused the 1980's full-size, in-grade tests.  For smaller
> pieces, the allowable stress increased; for larger pieces, the allowable
> stress was reduced.
> Prior to 1970, each lumber grading agency wrote their own grading rules
> determined allowable stresses.  Although the difference was not great, it
> not unusual to see different stresses promulgated by WWPA and WCLIB for
> same grade and species of wood.  The early 1970's were a transition in the
> lumber industry regarding "dimension" lumber, in which the grading, size
> allowable stress was standardized.  This uniformity does not extend over
> Beams & Stringers, or Posts & Timbers which are not "dimension" lumber.
> A. Roger Turk, P.E.(Structural)
> Tucson, Arizona

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