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Re: WOOD - Load bearing studs in a party wall

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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)