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Re: Shear Walls with Sloping Top Plates/Appendix B

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Sasha,

Glad that so many others are finding this information useful.

Yes, a roof slope that is considered shallow may be "steep" for the shear
wall.  When I design shear walls with sloping top chords, I size the strap
at the heel connection for the vertical component only.   The horizontal
component I assume to be carried by full-height sheathing.  Typically there
will be blocking at the eave-wall height (even if the gable-end studs are
full-height), since that's where the shear panel joint usually occurs.
(Just for fun, look at the next housing tract you see that's under
construction --I'll bet that the shear panels stop at the top plate level at
gable-end walls.)

Of the several others that I have spoken with about this, one SE suggested
that the vertical component from the roof diaphragm goes into the wall
studs.  If so, where does it go after that? Do end-nails from the sill
resist it?  Does the shear panel splice across the mudsill-to-stud joint
resist it--which would put the mudsill into cross-grain bending?

Another suggestion was that the roof diaphragm delivers only a horizontal
force to the sloping top plate.  If you are tempted to believe this, check
the bending stress in the roof sheathing due to the out-of-plane component
from a horizontal force.  For "steep" roofs, this could easily exceed 30,000
psi, which seems implausible for a plywood diaphragm.....

I hope to soon offer Appendix B for direct download from www.shearwalls.com;
for now you will need to request it by e-mailing me at matteson(--nospam--at)yosemite.net
with "Send Appendix B" in the subject line (not case-sensitive, quotes not
required).  It may take a day or more for me to respond over my ancient 56k
modem (33k on the upload side),  using limited e-mailing skills which send
the individual file separately to each person who requests the appendix.
(I'm looking forward to ICBO/ICC releasing this part of the copyright so the
world at large can have instant access to it.)

I would really love to see some TESTS of such shear walls.  The designs we
are seeing for custom homes (not to mention "real" buildings) today may rely
on a few such shear walls with extreme loads.   Anybody need a Masters or
Ph.D. project?

Thor Matteson

www.shearwalls.com


> From: "Alexander Sasha Itsekson" <sasha(--nospam--at)engstruc.com>
> To: <seaint(--nospam--at)seaint.org>
> Subject:  Re: steep pitched roof diaphragms and sloped shear wall top
chords
>
> I have a question for Thor Matteson and for others interested in the
topic.
> First, I wanted to take this opportunity to thank Thor for sharing
Appendix
> B of his book with the audience of this forum.  It is very valuable.
>
> The question relates to the connection of top plate to the low end post at
> the gable shear wall.  In the example provided in the above Appendix the
> total shear in the wall is 2500 lbs with the additional low end post
uplift
> reaction of 1250 lbs.  I am wondering if the metal strap installed at the
> top of the plate and bent down to be nailed to the post shall be sized for
> the total shear or for vertical component only.  Assuming the studs are
full
> height, how the horizontal component of the total shear is transferred
into
> plywood?  Do we need to add a row of blocking at the eave plate elevation?
>
> I think that the subject of that e-mail should also change to remove the
> words "steep pitched" because even with 4:12 slope and 4 kip shear wall
> load, you still get a vertical uplift of 1265 lbs.  Something to recon
> with...
>
> Any thoughts on this?
>
>
> Sasha Itsekson, SE
>
>
>


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