Tube Slip Joint Moment Connection
Tube Slip Joint Moment Connection
(OP)
I have a moment connection that I need to make work that consists of two tubes (snugly fit) nestled one inside the other. I have looked all over for information about what design checks may be applicable, but to no avail. The closest I could find was nested tapered utility pole calculations that used a linearly increasing distribution of the contact stresses. Does anyone have insight into how this issue might be calculated?
For specifics, the connection has a 2.875" diameter x 13 ga tube surrounding a 2.625" diameter x 11 ga tube with a 12" overlap. Additionally, the connection has two 3/8" through bolts.
Thanks for any insight that you may provide!
For specifics, the connection has a 2.875" diameter x 13 ga tube surrounding a 2.625" diameter x 11 ga tube with a 12" overlap. Additionally, the connection has two 3/8" through bolts.
Thanks for any insight that you may provide!






RE: Tube Slip Joint Moment Connection
What you describe sounds a lot like the style of connections that are used in stage lighting rigging pipes.
RE: Tube Slip Joint Moment Connection
The title of your post says this is a slip connection. Does the connection have to function as a slip connection and a moment connection at the same time? Seems like a conflict of interest.
RE: Tube Slip Joint Moment Connection
RE: Tube Slip Joint Moment Connection
Sorry about the confusion on the title of my post. Because of the removable nature of the connection, the tubes need to remain capable of "slipping" past each other once the two bolts are removed. A more appropriate title may have been "Tube Sleeve Joint Moment Connection".
@SAIL3: Those were my thoughts exactly. The tubes will deform into each other and hopefully transfer 100% of the moment. You are correct - this is definitely an engineering decision/opinion.
RE: Tube Slip Joint Moment Connection
As a lower bound, you could just use the capacity of the two bolts.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Tube Slip Joint Moment Connection
I agree, the capacity of the bolts could be used as a lower bound.
PS - When I googled that title, it was the first hit. I am not sure what the policy is about uploading or posting a link to the PDF, but if you can't find it and it is allowed here, I will post it.
RE: Tube Slip Joint Moment Connection
I question the pipes being disassembled without grease in the splice area. This implies not relying on any interstitial friction in the splice joint.
Mike McCann, PE, SE (WA)
RE: Tube Slip Joint Moment Connection
RE: Tube Slip Joint Moment Connection
RE: Tube Slip Joint Moment Connection
http://bura.brunel.ac.uk/bitstream/2438/7380/1/Ful...
Check out page 6 of this magazine:
http://issuu.com/pumasalient/docs/eis_31_web_pdf
A Florida DOT document on round tube slip connections - see page 37 and after on the document (page number not pdf page)
http://www.dot.state.fl.us/research-center/Complet...
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RE: Tube Slip Joint Moment Connection
RE: Tube Slip Joint Moment Connection
RE: Tube Slip Joint Moment Connection
Mike McCann, PE, SE (WA)
RE: Tube Slip Joint Moment Connection
The nice thing about the bolt couple is that it's reliable and easy to calculate. I like a theoretical discussion as much as the next guy but, truly, if this crossed my desk as production work, I would start with the bolt couple. If that worked, I'd move on; if it didn't, I'd start looking at other mechanisms. Additionally:
1) Why two bolts if not to establish a couple? Redundancy? I would hope that there isn't enough axial load in a system like this that it couldn't be handled by a bolt in double shear.
2) For a structure with human occupants, I'd feel better if the bolt couple worked as a back up mechanism for moment transfer.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Tube Slip Joint Moment Connection
I would see this as the inner tube being in initial radial compression and the other tube being in initial radial tension, due to the fit-up of the two. The magnitudes of those forces and stresses will be a function of the class of fit btwn. the two. The two bolts through the joint essentially maintain the fit btwn. the two tubes and should not have any play or the fit-up loosens very quickly. These holes should be match drilled or bored and a very tight fit. They really only carry the vert. loads above the joint. Then, you superimpose a moment which varies from max. compression to max. tension over the length of the overlap, or max. compression on one end and side to max. compression on the other end and other side. That couple is approx. 2/3rds of the lap length (assuming triangular pressure distribution) times bearing pressure resultant vectors/reactions. The max. bearing stress btwn. the two pieces of tubing is likely not exactly linear over the length of the overlap. But rather, likely zero to max. fairly quickly at each end of the overlap, curved in shape, and then fairly linear over the mid part of the overlap.
RE: Tube Slip Joint Moment Connection
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.