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RE: Stripping Treads
- To: <seaint(--nospam--at)seaint.org>
- Subject: RE: Stripping Treads
- From: "Garner, Robert" <rgarner(--nospam--at)moffattnichol.com>
- Date: Fri, 29 Sep 2006 14:57:45 -0700
If there aren't enough threads for a nut,
will there be enough threads for a coupler.
I had this problem once and the steel
erector brought out a magnetic base drill with an annular cutter and
countersunk around the anchor bolt just deep enough to get "full
nut". Fortunately, the base plate was thick enough to do this.
From: Roger Davis
Sent: Friday, September 29, 2006
Subject: Re: Stripping Treads
Another way of dealing with that problem is to put a coupler on the
exposed bolt and add another short threaded rod. Then cut the base plate hole
larger and use plate fillers and washers to get you to a point that a nut works
properly. I would trust that solution more than I would trust a welded
SDS Architects, Inc.
I’m looking for the design equation for stripping
threads. I have anchor bolts in tension and the bolt doesn’t extend
through the nut. Now I have to sharpen a pencil and see if the design
tensile force is less than what would strip what is left of the threads on the
bolt. If not then the contractor will need to weld an extension onto the
I’m having a difficult time finding design literature
on this. AISC doesn’t cover bolts. Logic tells me it is the
area of shear of the pitch diameter of the threads. Since the pitch
diameter occurs midway between the peaks and valleys, it would be ½ the
perimeter area of the threaded section put in shear by the tension force on the
nut/bolt. I found a reference for a bolt guide in one of Harold S old
posts to a 1998 NASA RP-1228 “Fastener Design Manual”. In
this report they recommend using 1/3 the perimeter area of the pitch diameter
to account for loose fit of the nut and bolt. It makes sense to me.
The equation is P=(PI*DIA*Fs*L)/3 where DIA is the pitch diameter. It is
written for yield strength and ultimate tensile strength. I was going to
input 0.6*Fy and 0.5*Fu to come up with allowable loads.
I’ve been searching other books and haven’t
found any reference to analysis or design recommendations for stripping forces
on a thread. Surely there had to be some recommendations prior to the
1998 NASA report. Can anyone give me other references to analysis and
design of bolt thread stripping?
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