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Re: WOOD - Load bearing studs in a party wall

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If I understand your approach properly, I believe you are suggesting to use
the full depth for l/d purposes to determine the allowable axial stress but
to
use a reduced area for the determination of actual stresses. If this is what
you are suggesting, it sounds similar to a steel member with a large b/t
ratio and determining the Qa factor. Based on this analogy, it appears to
have technical merit. The problem I have is that I've never seen this
approach
used in wood design (doesn't mean it's bad), but debating with plan checkers
has lost a lot of its luster in the last 20 years. I think I prefer to add
fire blocking
to reduce the weak axis l/d ratio. But I think your suggestion is a creative
one.

Thanks for the help,

Bill Allen
-----Original Message-----
From: Stan Johnson <hawneng(--nospam--at)wac.com>
To: seaoc(--nospam--at)seaoc.org <seaoc(--nospam--at)seaoc.org>
Date: Wednesday, October 22, 1997 8:03 PM
Subject: Re: WOOD - Load bearing studs in a party wall


>
>
>Bill Allen wrote:
>
>> I am checking the load bearing capacity of a wood framed wall that is
>> intended to be used in a party wall. This party wall consists of 2x4
studs @
>> 16" mounted on 2x6 top and bottom plates. These studs exist on each side
of
>> the wall. In other words, there are 2x4 studs @ 16" framed flush to one
edge
>> of the sill plate and 2x4 studs @ 16" framed flush with the other edge of
>> the sill plate. These two "rows" of studs are offset so that there
actually
>> exists 2x4 studs @ 8".
>>
>> In a "normal" wall, these studs are laterally braced on both faces. For
an
>> interior wall, there is gypsum wallboard on both sides. For exterior
walls,
>> there is some kind of exterior sheathing (plywood or stucco) with gypsum
>> wallboard on the interior. Therefore, these studs are laterally braced
>> continuously about the minor axis. To determine the axial capacity based
on
>> l/d ratios, I have used the distance between the sill plate and top plate
>> for my "l" and the depth of the stud for my "d".
>>
>> In this party wall case, there is gypsum wallboard on only one face of
the
>> studs. True, it is the compression face for the Code mandated 5 psf
>> partition load, but one edge is still laterally unsupported. My gut
feeling
>> is that the capacity of the stud is somewhat less than if there was
gypsum
>> wallboard on both faces but a lot more than if there was no gypsum
wallboard
>> at all.
>>
>> Since I realize that I'm not the first structural engineer to be asked to
>> use a party wall as a load bearing wall, I am curious what others have
done
>> in the past to determine the capacity of studs laterally braced on one
face
>> only.
>>
>> Regards,
>> Bill Allen
>
>Here's an idea.  I think its on the conservative side of things, but maybe
its
>better than nothing.
>
>Imagine that the stud is composed of two parts.  One is a 1.5" x1.5" square
that
>is fairly well braced because it is right next to your sheathing.  The
other
>part is away from the sheathing and is a little squirrely.  Find an
allowable
>load for the good piece using d=3.5" and Area=2.25 in^2 and then neglect
the bad
>piece (all it does is give the good piece an excuse to use d=3.5").
>
>
>Stan Johnson, PE,  But do you think this "good stud - bad stud" approach
will be
>effective with you local plan checker?      :o)
>
>
>
>