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Screw Pullout Values

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-----Original Message-----
From: Gary Hodgson & Associates [mailto:ghodgson(--nospam--at)bellnet.ca] 
Sent: Tuesday, June 07, 2005 8:31 AM
To: seaint(--nospam--at)seaint.org
Subject: Screw Pullout Values

I'm looking for pullout values for screws in oak parallel to the 
grain.  Does anyone know of any net resources regarding this?



Gary,
I designed a small stick-framed building a short time ago, and wanted to
use lag screws in withdrawal.  I could have gone to the NDS as Bill
Polhemus suggests, but in my youth I had a number of bad experiences
with hardware store lag screws repeatedly breaking during installation,
regardless of pilot holes, thread lubricant, and chanting over an
incense holder.  Thinking to step up in quality, I went to Simpson's
catalog and looked at their screws.  Nowhere in their catalog do they
give a withdrawal value.  Mind you, I'm talking about side-grain
withdrawal; they feel it's too unpredictable to tabulate.

Needless to say, end grain withdrawal is just that much less
trustworthy.

Now, when I'm not worrying about my structures breaking their fasteners,
I do some woodworking as a hobby.  I just finished a set of oak
bookshelves where I used sheetrock screws in end grain withdrawal to
hold the shelves in dadoes in the sides.  Those things took up like they
were in rock.  In fact, I overdrove one and broke it, but it didn't
strip (seems to be a theme with me, breaking screws).

So, I guess my advice would be, use the NDS values with plenty of
conservatism, and make sure that the installer does everything right:
pilot holes, thread lubrication (wax, not soap, especially in oak--the
water drawn to soap will corrode screws in that acidic wood), keeping
away from checks and splits, and most importantly, don't let them
overtighten the screws.  You'll want to schedule plenty of inspection
time.  And, bring your incense holder and chant book.

FWIW,

Mike Hemstad, P.E.
St. Paul, Minnesota

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