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[SEAOC] Re: [SEAOC] Re: [SEAOC] Plywood Shear Walls on Metal Studs

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The point raised by Tom Harris about the pneumatic fastening tools not
driving the wood sheathing panels tightly against the framing is a good one.
APA recommends hand or other pressure to assure contact between the
sheathing and framing when driving fasteners with pneumatic fastening tools,
whether with wood or steel framing. On horizontal surfaces such as roofs or
floors, foot pressure usually is adequate if placed near where the fastener
is being driven.  Otherwise, the tool driver does not have enough impact to
force the sheathing against the framing, and a gap will result. Mostly
common sense is needed, but the engineer or inspector needs to remind the
contractor/carpenter to follow this recommendation. 

In monotonic and cyclic load tests, wood sheathing fastened to steel framing
for shear walls (and diaphragms) can develop some pretty good shear loads,
depending on the fastener and spacing used. The screws or knurled pins
(nails) seem to "lock into" the framing and not pull out, but they do
rotate. As noted, Erico (ICBO ES #4144) and Pneutek (ICBO ES #3447) have
recognized shear values for this application.  AISI has a code change (#240)
for the 1997 UBC that will add shear wall values for this application in the
body of the code; it is based on limit states or LRFD design, so values must
be reduced for ASD.

John Rose/ APA, Tacoma

>     I would not use ubc values for steel studs. The screws/ pins do not have
>embedment  into a stud as in wood. American Iron and Steel Institute :
>1-800-79steel  has tables for screws but the values seem too high.
>     Erico has air gun pins ( ICBO # 4144 ) with values that also seem high.
>I have used these on two jobs and was very disappointed: The pins do not pull
>the plywood tight against the studs. I would recommend not using these. 
>     I have another large custom home under construction near the L.A. /
>Ventura County line just off the 101 freeway if you are in the L.A. area and
>would like to see one , it is at the corner of Kanan Rd. and Dawn Meadow,
>Westlake Village.
>Tom Harris SE
>Thousand Oaks, CA