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RE: What Is The Material Spec For "Lag Screw"?

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Yeah, actually I have this book, and that's the paragraph that got me
thinking about it. The "8D" part is actually in the specification, but it
doesn't say where it came from.

As I said, I calculated, for a 5/16" diameter lag bolt assuming A 307, that
the steel strength is a wee bit over 800#, which sounded reasonable to me. I
think in that case that the "8D" rule would be just about right.

William L. Polhemus, Jr., P.E.
Polhemus Engineering Company
Katy, Texas
Phone 281-492-2251
Fax 281-492-8203

> -----Original Message-----
> From: Roger Davis [mailto:rdavis(--nospam--at)]
> Sent: Monday, June 04, 2001 7:20 AM
> To: seaint(--nospam--at)
> Subject: RE: What Is The Material Spec For "Lag Screw"?
> "Wood Engineering and Construction handbook", Second edition by Keith
> Faherty and Thomas Williamson on page 5.45 says "Lag screws in withdrawal
> can, if long enough, develop loads in excess of the yield strength of the
> steel.  Therefore, the length allowed in calculating the
> withdrawal load is
> assumed to be approximately 8 times the shank diameter."

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