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RE: Bolts with Threads Excluded

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Chris:

I happened to be reading a report entitled "High Strength Bolts for Bridges"
by J. Yura, K. Frank, and D. Polyzois at the University of Texas at Austin
(1987).  The report mostly focused on galvanized bolts (which I plan to
bring up in a different thread soon), however, they discussed bolt shear
failure tests.  They don't address your concern exactly, but, I think this
is interesting:

Apparently, the 0.7 reduction factor commonly used for the design of bolts
in shear is based on the root area of the threads.  The shear plane,
however, is not the thread root area, since passing a plane perpendicular to
the bolt would only pick up part of the root area, and part of one of the
threads as well.  The shear area is more than the root area and less than
the gross area.  The authors tested bolts loaded through the threaded area
and bolts loaded through the gross area and found a reduction factor between
0.8 and 0.85, not the conservatively used value of 0.7.

Like I said, this doesn't really address your question, but maybe this plays
a part in traditionally allowing some of the threaded area into the shear
plane.

> -----Original Message-----
> From:	Serroels, Chris/SAC [SMTP:CSerroel(--nospam--at)CH2M.com]
> Sent:	Monday, February 15, 1999 9:54 AM
> To:	'SEAOC'
> Cc:	Hinman, John/BOI; 'Holloway, Lee/HNTB/SEA'
> Subject:	Bolts with Threads Excluded
> 
> What constitutes "threads excluded" for a high strength bolt.  Does the
> start of the threads have to be a certain distance from the shear plane?
> How about the taper?  The bolt I'm looking at as I write this has a
> roughly
> 1/8" long taper between the solid shank and the start of the threads.
> 
> The RCSC commentary says "Inclusion of some thread run-out in the plane of
> shear is permissible".  Does "thread run-out" include the taper?   Another
> reference, The Structural Steel Designers Handbook, states "It is common
> practice to allow the last 1/8 in of vanish thread to extend across a
> single
> shear plane".  Does "vanish thread" include the taper?
> 
> This comes up because a job I designed is under construction, and we noted
> on the plans that all bolts were to be "threads excluded".  The first
> handful of bolts that have been installed have a few threads plus the
> entire
> taper inside the shear plane.  I am tempted to require that all threads,
> including the taper, be outside the shear plane, however what I've read
> indicates otherwise.  This decision could cause the Contractor, and
> subsequently me, some grief as the Contractor has already ordered tens of
> thousands of bolts.
> 
> Thanks in advance.
> 
> Chris Serroels
> CH2M HILL/Sacramento
> 
>