From: Charles Greenlaw <cgreenlaw(--nospam--at)speedlink.com>
Date: Mon, 28 Jun 1999 10:49:10 -0700
Mark Swingle, SE, wrote:
>In your post you said the
>94 UBC removed the equivalence between common and box as far
>as the sw table is concerned. Am I missing something?
CG: No, you got it right. It was me who mistakenly looked at the horizontal
diaphragm table instead of the vertical shear wall table in the 94UBC and I
saw no mention of "box" nails. I stand corrected. Commons and galvanized
"box" nails are equivalents in the UBC shear wall tables through the 97
edition. See below about test results that support the idea that commons and
plain "box" nails do have substantially equivalent performance for shear
As an aside, I hate to harp about nomenclature, but the SE community is
revealing a lot of ignorance about nailing in generically calling every type
of nail thinner than commons (thinner for the same basic length) "box" nails.
I realize that the UBC has long carried a table that gives lengths and wire
gages for "box" and "common" nails only, but considering how strongly the SE
community controls the UBC in seismic- related matters, for SE's to point to
the UBC as an EXTERNAL source of authority is rather circular and disingenuous.
Nails used by framers are seldom either commons or box nails.w Morover,
there are several varieties of "box" nails among those actually labeled box
nails, depending on edition of federal spec FF-N-105B and on which version
of box nails in ASTM F1667-95 is used. For 10d and larger, "box" nails of
the two varieties are either thicker or thinner than sinkers and coolers,
hence the need to specify by length and decimal diameter if one cares.
I was recently reminded of the plywood shear wall cyclic test results
reported by Ficcadenti, et al, in the 1997 SEAOC Convention Proceedings.
These tests, conducted at UC Irvine, made direct comparisons between 8d box
nails (.113"diam) at 3"oc and 8d common nails (.131" diam) at 3"oc in 8ft x
8ft shear walls, and with respect to four different plywoods: 3/8 CDX and
Struct I, and 15/32 CDX and Struct I. In each case, 2x4 framing lumber was
used except at hold-downs, which had very robust custom-made devices on 4x4's.
The tests followed both ASTM E564 (1984) and SEAOSC's 1996 cyclic testing
protocol. Racking displacements up to 3 inches each way from vertical (3
percent drift) were obtained, but the main interest for comparisons was the
0.5, 1.0, and 1.5 percent drifts.
Common nails had somewhat better resistance at low drifts than the same
number of box nails, but the box nails had "somewhat greater strength" than
commons at high drifts. "The specimens constructed with box nails maintained
their strength at greater drift levels than the specimens constructed with
common nails." The explanation was felt to be in the lesser beam stiffness
but greater psi strength of the box nail's wire.
There is an earlier run of tests on common vs. box nails reported in the
1995 SEAOC Convention Proceedings; similar outcome, even where box nails
were in part overdriven and the commons were all precisely flush. Energy
absorption at high drifts was reported superior with box nails as well.
Additionally in the 1997 report, hot-dipped galvanized box nails were
compared directly to plain box nails, but only in 3/8" plywood specimen
panels. Test strengths were THE SAME: "The galvanizing does NOT appear to
have any effect on the strength of these plywood shear wall assemblies."
I also received privately some additional info regarding the Ficcadenti/ UC
Irvine shear wall tests. This source agrees that framers who were consulted
prefer the smaller nails, 10d box (.131*) & 8d box (.113) over 10d common
(.148) for reasons of less damage to the framing timbers. The report itself
states that "pneumatically driven box nails are typically used in
construction." (* other plausible 10d diameters are .120 for sinkers and
coolers, and .113 or .128 for box versions.)
Rather sadly, this same source reports that these tests, conducted in
accordance with current ASTM and SEAOSC desires, were very poorly received
by the established SE community, and were attacked as supporting inferior
and shoddy construction.
Even sadder is the apparent need of this source to avoid going public to the
listserver about this.
Once again, here's the specter of "religious" -type dogmatic beliefs trying
to control what's to be deemed good practice in in a profession that still
somehow claims to honor objectivity and to welcome truth-seeking.
If Structural Engineers as an organized body can't even get things straight
and stay honest about nails and nail performance, then in what matters can
they be trusted to get ANYTHING right?
Not much that I'm willing to trust anymore.
Charles O. Greenlaw SE Sacramento CA