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# RE: Bending Threaded Connection Design

• To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
• Subject: RE: Bending Threaded Connection Design
• From: Mateusz Podskarbi <podskarm(--nospam--at)2hoffshoreinc.com>
• Date: Wed, 16 Jul 2003 17:50:48 -0500

```Bob,

I have resolved this in issue in the similar way to what you've suggested:

First, I assume that the BM in the rod is fully transferred by the shear
Second, I calculate the shear capacity of the threads and distribute it
along the circumference of the rod.
This results in the shear capacity per unit length of the rod circumference.
Third, I calculate the force per unit length that BM induces at the threads.
I do it, using the formula for the bending stress in the very thin ring and
multiplying it by the thickness of the ring.
Fourth, I add the force per unit from bending to force per unit from axial
load and compare this force with the shear capacity of the thread.

It's not a design, but rather a quick check if the concept has a chance to
work.
It looks like it does (at least looking at this aspect of it)- the maximum

I think the method described above makes some sense.

Regards

Mat

-----Original Message-----
From: Bob Kazanjy [mailto:rkazanjy(--nospam--at)uci.edu]
Sent: Tuesday, July 15, 2003 7:59 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Bending Threaded Connection Design

Mat-

I'll take a shot at it.......

shear & bending),  for bending I would check to see if the connection
was adequate to develop the moment capacity of the rod.

The maximum plastic moment of the rod must be able to be resisted by the
threaded joint.    For axial load only the 5/8" wall thickness would be
inadequate (unless the plate was substantially higher strength than the
rod).

However for a bending application the rather small engagement of the
plate might be enough (again depending on the relative strengths of the
plate & the rod).

I would look at it as follows......the top portion of the threads (say
10 o'clock to 2 o'clock) and the bottom portion of the threads (4
o'clock to 8 o'clock)  as creating a resisting couple.  Not unlike the
steel and the concrete compression block in a RC section.  These
resisting portions (sectors of the complete rod circumference) are just
gut level estimates.

Play around with the numbers and see if you can generate the required
plastic moment for the rod with reasonable sector sizes which
(hopefully) will result in reasonable plate thread stresses.  I'm
guessing that the plate is weaker than the rod.  My gut says that
although 5/8 plate is kind of thin to be accepting a 2" rod but a 2" rod
doesn't have a huge bending capacity.  The whole thing just might work out.

regards
Bob  Kazanjy, PE
Department of  Civil Engineering
UC Irvine

Mateusz Podskarbi wrote:

>List,
>
>The steel cantilever rod (2in OD) is screwed into the steel wall
>(0.625in WT). Does anybody know any basic reference for designing the
>threads between the rod and the wall?
>>From the information I have found, it is quite straight forward, how
>>to
>design the threads when the bolt is under axial load. Unfortunately, I
>have no luck with finding the answer, when bending is included.
>
>Any help will be greatly appreciated.
>
>Regards,
>
>Mat Podskarbi
>2H Offshore Inc,
>Houston, TX
>
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