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Wood Fire Rated Wall Assembly F'c reduction

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thanks John. AF&PA has developed a couple of webpages with more details on the
2x6 tested assemblies. the following links cover insulated and non-insulated
assemblies, respectively:

http://www.awc.org/dca/dca3/2x6ins.html
http://www.awc.org/dca/dca3/2x6noi.html


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From: John Rose <jrose36(--nospam--at)earthlink.net>
To: seaint(--nospam--at)seaint.org
Subject: Re: Wood Fire Rated Wall Assembly F'c reduction


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The reduction factors for load-bearing studs are in the UBC and in
Underwriters Laboratories specifications to "calibrate" current design
methodology per 1997 NDS back to originally-tested Fc-perp values (385
psi for Douglas fir). This was done so that old designs would not have
to be retested.

AF&PA has recently addressed this issue with new fire tests on
load-bearing wood framed walls (2x6) with Fc-perp value of 625 psi.  It
requires longer gypsum wallboard fasteners (2-1/4" Type S screws spaced
7" oc were used in the tests), so that the fastener penetrates into
uncharred wood at the end of the 1-hr test to retain the gypsum
wallboard attachment.  The tested walls had 5/8" Type X gypsum wallboard
on both sides (symmetrical construction).There are plans to test with
2x4 framing, and also non-symmetrical construction with wood structural
panel sheathing on the unexposed side of the wall.

John Rose/APA - The Engineered Wood Assn. (Tacoma, WA)
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To: seaint(--nospam--at)seaint.org
From: Neil Moore <nmoore(--nospam--at)innercite.com>
Subject: Re: Wood Fire Rated Wall Assembly F'c reduction

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Jeff:

At 04:51 PM 01/03/2000 -0800, you wrote: 
>
> The Uniform Building Code requires that the design stress for studs be
> reduced to 78 percent of allowable F'c for all 1-hour rated walls.  This
> appears in a footnote #18 for Table 7-B.
>   
> Jeff Albert
> KPFF Consulting Engineers
> Seattle WA


We reviewed Table 7-B (1997 UBC Volume 1) and have the following comments:

1.      Apparently these are new provisions as these notes aren't in the 1994
UBC.
2.      These additions (there is also additional fastener length
provisions in
Note 17) were not flagged with a black vertical change bar.
3.      The ICBO errata has no comments concerning the above items.
4.      There are other footnotes in Table 7-A and Table 7-B  that have
changed
or been added that were not flagged. 

This appears to be an oversight on the part of ICBO.  Would suggest that they
review all of the footnotes throughout the 97 code and alert us to other
non-flagged changes on their web site.

Guess I'll have to modify a couple of spread sheets now.

Neil Moore, S.E.



From: "Jeff Albert" <jeffa(--nospam--at)kpff.com>
To: <seaint(--nospam--at)seaint.org>
Subject: Wood Fire Rated Wall Assembly F'c reduction

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The Uniform Building Code requires that the design stress for studs be =
reduced to 78 percent of allowable F'c for all 1-hour rated walls.  This =
appears in a footnote #18 for Table 7-B.

First, my question is whether other engineers in California, and other =
UBC states are applying this provision to their wood design.  Also, how =
have building officials responded / reacted to designs not using the =
reduction.  I will note that it is my belief that a reduction is =
unnecessary, and that designs done without using the reduced values are =
safe.  But this brings me to my second question.

If this provision is being waived away, what are the liability concerns. =
 I am particularly interested in projects that are condominiums.  With =
the state of condo associations these days, it seems to me that not =
adhering to a specific provision in the code leaves the design open for =
problems if reviewed at a later date.

Finally, is anyone aware of any new studies, or fire assembly testing, =
etc. that is currently being done that might address this issue.  My =
understanding of the reason for this provision is due to a change in =
allowable perpendicular to grain design stress values which were not =
reflected in the original fire assemblies tested.  Therefore, a =
reduction factor was applied which basically brought you back to where =
you were before the increased values.

I look forward to reading your responses.

Jeff Albert
KPFF Consulting Engineers
Seattle WA