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Re: wood framing question

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-----Original Message-----
From: Jim Warne <jwarne(--nospam--at)direct.ca>
To: seaoc(--nospam--at)seaoc.org <seaoc(--nospam--at)seaoc.org>
Date: Sunday, December 21, 1997 11:25 AM
Subject: Re: wood framing question


>
>
>Replying to the question of whether adding another plate at the top of an
exterior stud wall could affect strength in the horizontal plane, Dennis
wrote:
>
>> This would not be a problem .......
>> Dennis
>
>OK, Dennis, but how about a fourth plate? A fifth? At some point there's
going to be a weakness against wind loads, and the stack of plates is apt to
roll over because of an inwards or outwards reaction against the bottom
plate, from the top of the studs.
>
>A quick check of possible overturning moment under the maximum wind
reaction, and the restoring moent from dead load and nail tension would be
worth doing, to see if the third plate creates a weakness.
>
>> Jim Warne, Vancouver


Jim,
You may have a point if the loads were very high, but (without running the
numbers) my judgement would tell me that this is unlikely - especially if
the sheathing applied to the wall extends to the top plate. The type of
hinge that you describe is very common in platform framed construction,
however, the sheathing (whether it is plywood or lath and stucco) should
help to reduce this as well as the fact that each 1-1/2" layer is nailed to
the 2x below. If the top plate were, say, a 4x12 - then maybe I could see
your point.
If your judgement is to consider this a problem, then use some inexpensive
clips like Simpsons A35F on the inside and outside face of stud so that the
resistance to overturn at the hinge is reduced - however, I can't imagine
this as a problem if the plates are properly spliced with 16d at 4" o/c.
Finally, the question really wasn't about my opinion of six or eight plates
secured together, it was about adding a third plate to a weak chord connect.
I believe I also recommended the possiblity of using a strap at the
discontinuity in lieu of the added plate.
BTW, I have seen may instances where a third or fourth plate is used to
build up a header where only three or six inches is need to be level to the
top plate so as to maintain consistant plate height.  I never detailed this
but realized when building in the field that it was easier to stack plates
than put in 3" or 6" cripple studs.

Happy holidays to all,
Dennis