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Re: notes for Appendix B, Wood Shear Walls, Sloping Top Plates

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David,

Thanks for putting so much thought into this.  I could not get the Excel
file to do anything except display the text that was already in your PDF
file.  If you could, please e-mail me the file directly.

I first became aware of this while under the tutelage of a very wise SE.  He
was trying to determine the shear distribution within a within a trapezoidal
wall, because he knew that the tie-down forces would not be the same at each
end.   This can be found from the FBD of a trapezoidal wall.   From there it
got more tricky.  He felt that the distribution across the width of the wall
was parabolic, increasing from the tall end to the short end.

That is where our opinions diverged.  The triangle above the rectangular
wall area must be a "three force body" in order to satisfy statics (at least
that is the only way I have found to make it work).  Assuming that the
triangular portion is a three force body (when a body has three NON-parallel
forces acting on it, those three forces must all act through a concurrent
point) it works with the overall FBD of the wall.  I figured that the bottom
of the wall would not know what shape the overall wall was, which led me to
believe that the shear distribution would be uniform across the width of the
wall.

I am assuming that the horizontal shear from the triangular portion IS
transferred through the plywood (I will need to review the diagrams and
revise them to make this clear).

In my view, if you put a tie-down to the left of the short end-post (with
some means of tying it to the sloping top plate) you would pick up the
vertical force from that point leftwards.   Without seeing your spreadsheet,
it does not make sense to me to have a tie-down anywhere except at the end
of a shear wall.

Whatever happens within the boundaries of the shear wall must be compatible
with the statics of the wall as a whole.  I wish I had time to learn FEA and
delve into it more (hint to all you young whipper-snappers out there), or
(better yet) access to a testing facility.  It is a long jump from the basic
theory to reality for shear walls even if they are nicely rectangular.
Another wise SE reminded me that the trapezoidal shear wall shown in my
write-up was indeterminate, since the rafter was continuous beyond the tall
end of the shear wall.

Have fun!

Thor


===========================================
===========================================

I think I have a way.
my notes are too big.
Here they are in PDF
 http://home.winfirst.com/mrkgp/public_html/SE/trianglewallnotes.PDF
and again the spreadsheet is at=20
 http://home.winfirst.com/mrkgp/public_html/SE/trianglewall.xls

David Merrick, SE
Sacramento, Ca
MRKGP@WINFIRST>COM



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