From: Charles Greenlaw <cgreenlaw(--nospam--at)speedlink.com>
Date: Wed, 30 Jun 1999 02:24:26 -0700
At 07:49 PM 6/29/99 -0500, Ed wrote, with respect to what I had posted
earlier about box nail test results:
>>The explanation was felt to be in the lesser
>>beam stiffness but greater psi strength of the box nail's wire.
>Forgive my ignorance with the lingo, but what is meant by "psi" strength?
I was attempting to summarize the paper in SEAOC Convention
Proceedings of 1997, which should be consulted in the original. Every member
of a SEAOC local section is entitled to a free copy, but in modern times
they are no longer mailed out to everyone automatically. You have to get a
copy at the convention, or later request a copy from the SEAOC Sacramento
headquarters office. The Executive Director says most members do not want a
copy, hence the change in policy to save money.
I couldn't tell from the paper if it was the yield strength of box
nails that was better, or ultimate strength, or both. So I copped out and
called it the "psi" strength to avoid being more specific than I actually knew.
Apparently the box nails that were tested "wiggled" in flexure more
without breaking or pulling out, and have what was deemed to be an advantage
when an event happens that takes shear walls nearly to failure. I'm not
advocating intentionally taking plywood shear walls to the limit, but when
the high-stakes question arises after construction what a box-nailed shear
wall is good for compared to common nails, there is at least a tested basis
I am informed that additional tests that were reported in the June
1998 EERI publication found that gun driving gave superior results to hand
driving, for both common and box nails. The presenter who spoke recently to
Central Section of SEAOC said hand driving enlarges the hole due to
eccentric hammer blows. There is a velocity difference that perhaps may
affect the frictional grip against nail withdrawal.
>>Energy absorption at high drifts was reported superior with box nails
>Intuitively, it seems that in wood, less rigid fasteners would share load
>better and not tend to fail in a "zipper" effect as much as more rigid
>fasteners would. I hate to use a bolt thicker than 1/2" dia. in 2x trusses,
>but others feel 3/4" are a must to reduce the number of fasteners and,
>therefore, cost. To me, installing (8) 1/2" bolts is barely more work than
>installing (5) 3/4" bolts and makes much more sense.
I tend to agree, but there was a great deal of energy absorbing
deformation shown under the force vs displacement curves for both types of
nails. The differences were modest, and in degree, rather than in basic
nature of behavior.
A curiosity not explored in the reported tests is how an 8d box nail
would compare to a 6d common nail. Each has the same diameter at 0.113 in.,
and the 6d common is a little shorter, but still provides more than
code-specified penetration into framing. If 8d box nails in shear panels
"have no value" as some well-known SE litigation experts reportedly testify,
what are 6d commons good for?
And 16d sinker nails are identical in length and diameter to 12d
commons. Does the name make a difference to the performance, or only make a
difference in people's attitudes? Reputations and fortunes turn on the
answer, it appears.
Charles O. Greenlaw SE Sacramento CA