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Re: Design of Wood Top Plates

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I have seen many suggestions on this list, however, only one person alluded to
what I believe to be the correct solution, IMHO  :o)

I had this concern several years ago when just for kicks I tried to calc out
the double top plate of a stud wall.  To my amazement it didn't work, yet
just about 100% of all construction I have seen uses a double top plate.  I
called an engineer at NDS and he told me the following:

The top plate is in flat use.  The shear values given in NDS are for vertical
use taking into account splits.  The values in NDS are basically for vertical
use with 1-1/2 wide members.  The shear values in the code are given
expecting some amount of probable split, which I don't remember.  Anyway, the
important part is, when you lay it flat the likely hood of getting a
horizontal split almost disintegrates so the Ch factor in the code of 2.0
should be used to increase the allowable shear value.  Now think about it,
how many of you have seen a 2x split horizontally when you have loaded it in
the flat position.  I can not think of ever seeing it.  That's because before
the split would occur the member has failed in some other form.  It would be
very difficult to split a 2x4 or a 2x6 laid flat from shear.  That is why you
can increase the shear by the Ch factor.  He also told me off the record that
the shear values in the NDS tables were very conservative.

So if you use the Ch along with Cd you will probably not have a problem with
shear in a double top plate.

Just my $0.02


Richard Lewis, P.E.
Missionary TECH Team

The service mission like-minded Christian organizations
may turn to for technical assistance and know-how.