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RE: Plywood over light gage shear wall

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Correction:

 

That should have read, “…torsional load applied by the screw-gun…”   At the time, anecdotally, we guessed that the screw must have had too much trouble getting through the plywood because perhaps the tip was designed for cutting steel and not plywood, and that when it hit the steel the shank was already hot and fatiqued, but it was at about that point that the dang things just came apart, usually twisting the head clean off.  Finally, if I recall, we’re talking about roughly 15% of the screws, which at the time I thought was pretty significant.

 


From: Donald Bruckman [mailto:bruckmandesign(--nospam--at)verizon.net]
Sent: Thursday, May 24, 2007 9:28 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: Plywood over light gage shear wall

 

A note from the field.

 

Last time I did a project with plywood shear walls over metal stud, I noticed a lot screws broken off during the drive process. The installer complained that the screw shank was too thin, (I believe they were #8s or #10s although this goes back about 3 or 4 years.) but the EOR claimed bad installation. Whichever it was, as I stood on the scaffold and watched the installers beat up the screws and get frustrated, I got the impression that perhaps a very specific screw should have been spec’d rather than a generic note such as “No. 8 x 1-1/4” screw” (Don’t quote me on what was used, I don’t recall the exact callout).

 

Perhaps the framer did not have enough experience with the concept and didn’t know the proper way to drive the screw (this might be the problem because most metal stud companies are drywall companies and are rarely are given structural work to do) but for whatever the reason, clearly this crew was having big trouble with the screw they were using.

 

First, any experiences with this problem? Second, even though I had them fix all the bad screws, I couldn’t help but think about the status of the ones that appeared okay. Has there been testing to find out whether or not a specific screw shank can be weakened by the driving process; specifically by axial load applied to the shank by the screwgun?