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Lag Screws

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Thank you to all of you who responded to my questions on Lag Screws in
withdrawal, both on the list and privately.

There were a number of concerns which were raised by several people,
which I will address.

Several people mentioned the preference for through bolts or threaded
rods rather than lag screws.  Several other people then pointed out that
this would represent a pretty big loss of section for the truss bottom
chords.  That pretty much eliminated threaded rods from consideration.

A couple people were concerned over the extra load to the trusses.
These are new (not built yet) trusses, and so would have been designed
for it, as well as the relatively small loss of section due to my
supposed 1/8 inch diameter pilot hole.

However, the crux of the issue is that no manufacturer will publish
allowables for their product in withdrawal, and they must have a reason.
I suspect the reason is that the screws break at the top of the threaded
area too often for comfort.  As I said, that was my experience,
regardless of how careful we were with pilot holes and thread lubricant.

The simplest idea, to pass a strap around the truss chord, was not
practical here because I am at midspan of the truss and there may be
vertical or diagonal members in the way.

What I ended up doing was supporting it off the floor with a pair of
studs at each end.  The beam changed from a W12 to a pair of LVL's to
make the attachment easier.

Thanks again for all the help.

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

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