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Re: Lag Screws

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How about welding some tab plates to the top flange,
sistering/scabbing some 2x's to the 2x bottom chord,
and drill and bolt through?  Definitely, double check
with the truss mfr if they haven't already acct'ed for
those moving/suspended loads in the design and
fabrication...
David Topete, PE
SF, CA
--- "Michael L. Hemstad" <hemstad.ml(--nospam--at)tkda.com> wrote:

> List,
> I have a project where I need to hang a small steel
> beam from the bottom
> of some prefab wood (2x) trusses to carry the track
> for a moveable wall.
> The beam will cross about 7 trusses.  It's stiff
> enough to spread out
> the load to the trusses.
> 
> The simplest idea I have come up with is to use lag
> screws through holes
> in the top flange of the beam, into the bottom
> chord.
> 
> Simpson, for example, makes a 1/4 inch diameter lag
> screw, with catalog
> values for strength in shear.  However, they
> corporately refuse to give
> me a withdrawal value for it.
> 
> The NDS has values--rather large values--tabulated
> for generic lag
> screws.  I could just use those.  However, in my
> earlier days (say, 20
> years ago) I occasionally fastened pieces of wood
> together with lag
> screws.  We shied away from the smaller ones because
> they often broke
> during installation.  We drilled pilot holes, we
> waxed threads, we
> sacrificed black chickens before we screwed them in.
>  5/16 screws broke
> maybe one time out of four; the 1/4 inch ones broke
> more often than not.
> 
> Relating this fascinating story to the Simpson
> engineer, she said that
> her understanding was that current lag screws were
> better than those of
> twenty years ago, and theirs, being of hardened
> steel, were better than
> the ones we bought at the hardware store.  She
> simply was not allowed to
> give me a withdrawal value.
> 
> It would be easy to just use a bigger screw, but the
> truss manufacturer
> is going to be excited enough as it is with the 1/8
> inch pilot hole I'm
> calling for in his bottom chord.  And I could bring
> straps up the side
> of the truss chord, but it's at about midspan and
> there is probably a
> metal truss plate there that doesn't want holes
> drilled in it, and
> vertical or diagonal members that preclude strapping
> over the top of the
> chord.
> 
> So, finally, the question:
> Can anyone comment on the quality and viability of
> 1/4 inch lag screws?
> Or does anyone have a better way to solve this
> simple problem?
> 
> Thanks,
> 
> Mike Hemstad, P.E.
> TKDA
> 
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