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RE: horiz. diaph.

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IMHO, the main difference is that the panel is more forgiving to overnailing
which plagues 4 ply panels. This is of less importance when dealing with a
low-load horizontal diaphragm than with shearwalls.
I make sure that I specify 5-ply panels in vertical shearwalls since I
expect the contractor to overnail more than 20%. As long as he does not
penitrate more than one ply, I can still obtain the same values as I would
if I used a 3/8" panel.
Most of the builders want to save money by using 3/8". Based upon my
personal observations, I won't allow it unless the builder has a history
with me where I am assured that he either hand nails or can control the
pressure of his tools.
I don't think that there is any difference between a four or five play
vertical panel in capacity strength. I don't have a code in front of me, but
remember that vertical shear panels of 3/8" thickness can be increased in
capacity to match 15/32" capacities as long as the studs are spaced at 16"
on center. Therefore, the only advantage I can see to 5-ply panels is the
contol that you gain by defects in nailing that occur in the field.

Dennis Wish PE

-----Original Message-----
From: Mark D. Baker [mailto:shake4bake(--nospam--at)]
Sent: Tuesday, June 30, 1998 11:18 AM
To: seaoc
Subject: horiz. diaph.

What is the advantage of 1/2"- 5 ply horizontal diaphragm vs. 1/2"- 4
ply, both str. 1? Am I correct in saying the allowable diaphragm  shear
for a given nailing/blocking is the same but the allowable vertical load
carrying capacity (d+l) is different?

Mark D. Baker