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RE: Rolled Threads

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Nels,

I believe that Mark is correct in noting that threaded rods with rolled
threads have a smaller shank diameter than the threads (For both cases
however, your thread diameter is the same).  This CAN give the rolled
threads a smaller capacity.  You should probably look at the actual rods...
For cut threads use .33*Fu for an allowable tensile stress (fracture), for
rolled threads you should use 0.6*Fy for an allowable tensile stress
(yielding).  Neither of those allowables includes a stress increase or
stength increase.  These should be applied as per the particular code
requirement (i.e. older codes allow 1/3 increase for winds, seismice usually
allows an increase in allowable to account for strength base loads (+- 1.6)
)

HTH,
Greg Effland, P.E.
KC, MO USA



-----Original Message-----
From: Nels Roselund, SE [mailto:njineer(--nospam--at)att.net]
Sent: Monday, March 25, 2002 10:27 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: Rolled Threads


Mark,

I'm confused by what you are describing.  You seem to be describing a bolt
with upset threads, that is, a bolt with threads that have a larger diameter
than the shanks.  I've never seen a bolt like that unless it were a special
fabrication.  The bolt shank diameter and the diameter at the threads are
always the same.

The threaded fastener illustration on page 4-147 of the aisc 9th edition, or
Table 7-4 of the aisc lrfd 3rd edition, refer to ANSI B1.1.  The 3rd edition
shows the thread diameter to be db, which is noted to be the bolt diameter.
Are you saying that there are bolts with bolt diameter that is defined by
the diameter at the threads, but that have shanks that are of lesser
diameter?

Also, you seem to be saying that rolled threads will [or may] result in a
bolt that has diameter at the threads greater than the diameter at the
shank.  My understanding has been that rolled threads are applied to a rod
by forming the threads into the round rod under pressure with no loss or
addition of material, while cut threads are made by removing material, but
that both procedures result in the same finish configuration.  Are you
finding that this is not true?

Nels Roselund
Structural Engineer
South San Gabriel, CA
njineer(--nospam--at)att.net



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