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[SEAOC] Plywood: sinkers beat common nails?

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Say it isn't so!

Someone has to reassure me. I've just lectured a poor framer about the thin
gun-nails he used in the shear walls, when I had asked for Common Nails in
the drawing notes. It now seems that he may have been right, after all. 

He said (as they all do), "Everyone uses gun driven nails...you can't pull
these suckers out...they're stronger than common nails...you can't avoid
over-driving, 'cause the wood is uneven..."

Well, of course, I asserted my authority.  By towering up to my full 5'-6"
height, and raising my voice to "shrill", I finally got him to agree to
re-nail. When I got home, I looked for something in my SEAOC literature to
back my claims up. I was sure I'd read that thin "sinker" nails were weaker.
Also, "everyone" knows that over-driving the nails spoils the shear strength.

There's a paper from the '95 SEAOC convention that says the contractor is
right. Seb Ficcadenti and Thomas Castle, principals in a consulting firm;
and Deborah Sandercock and Robert Kazanjy, from the University of California
at Irvine; built some model 3/8" plywood shear wall panels with a variety of
nailing arrangements and tested them under simulated earthquake shear
loading. Some had common, some had sinker (or "box") nails, and some had
20%, or 50%, or 80% of the nails driven 1/16" or more into the sheathing.

Their conclusion was that...The 3/8" thick plywood panels with box nails
were as strong or stronger than those built with common nails...overdriving
the nails adversely affects the strength, but not below that of the
comparable common nail panels... the box nail panels have a greater residual
integrity after the test than common nail panels.

The rationalle presented in the report, to explain the poorer performance of
common nails, is that the box nails they used had larger diameter heads. The
common nails they used also had a conical shaped head (the underside was
tapered, something like a countersunk screw's head shape). That was why,
they surmised, that the common  nails pulled through the plywood more often
than the box nails. The box nails usually pulled only part way out, and
dissipated more energy.

I think I was still right about the nailing I rejected on my project,
because the Senco gun nails "my" framer used were even thinner, and had
smaller heads. Those heads also had "cookie bites" out of one edge, to fit
tighter in the nail strip. These sharp edges enhanced the tendency of the
nails to cut through the top veneer.

I also don't think I've seen conical heads on our common nails. I think they
all have a flat underside. I believe they would resist pull-out better than
the nails used in the UCLA Irvine test.

Here are my two questions:

 1.      Are there any other reports of testing of plywood shear wall or
diaphragm panels, comparing common nail performance with thinner
"sinker" or "box" nails?

2.      What evidence is there that "overdriving", that is, driving nail
heads         into the plywood deep enough to cut the top veneer, weakens
shear                resistance?

I had a few more questions, like, how to get contractors to believe we
REALLY MEAN the notes on our drawings; and how to get them to treat me with
respect; but I'll save those for another time.

                                                        Jim Warne

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