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Re: Lag Bolt Zperp values in thin members

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It reminds me of the work recently published in the JLC (at V.I.T. maybe?)-- but their recommendation was 1/2" dia. lags at 7.2" o.c. for 12' joists.
Chuck Utzman, PE

Jordan Truesdell, PE wrote:
I've just run across an interesting table in the Virginia version of the 2003IRC, and wonder what others thoughts are on the matter. The table in question is R502.2.1.1 (you can see the VA table here ) and it gives ledger lag spacing for deck connections to residential construction.  If you back calculate the spans, you get 375# per 1/2" lag. For example:

12' deck joist span,
50psf TL (10D/40L I'm assuming),
1/2" diameter lag screw through a
        2x S. Pine ledger and
        2x solid sawn rim joist (no species provided, SPF is the most common solid sawn rim material)
so 12'/2 (trib) x 1' x 50psf  = 300#/ft

For a 12' span, the table requires a 1/2" dia. lag on 15" centers. So 300#/ft x 1.25' = 375#.

That's all well and good, except that according to the 2001NDS:

1) a single shear connection for a 1/2" lag for a 1.5" side member when loaded perpendicular to the grain is 250# when the penetration into the main member is 8x the lag diameter, or 4".  and

2) The minimum penetration is supposed to be 4D, which you cannot have with 2x lumber, even if you count the sheathing (7/16"+1.5" < 2").  Even at the minimum penetration of 2", the allowable shear value is only 125#.

3) The table value I gave was for S.Pine/S.Pine., for SPF the value drops by 25%.

Stranger yet, the values for through bolts are nearly double (29" vs 15") at the 12' deck span.  725# for a single 1/2" through bolt? NDS gives 330# for 1-1/2" to 1-1/2" w/ side member loaded perp to grain.

I hadn't taken the time to calc out these numbers until this morning, when I got a call on the ledger attachment for a deck with a hot tub.  I assumed that lags couldn't be used with the tabulated values, but that the VA code officials had a specific analysis done for the short penetration. Looking at the table more closely, the numbers make no sense. I haven't seen a mention anywhere of the values determined through testing. Am I missing something technical here?

Thanks to those who made it this far.

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