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Assessing "Swaged" Connections in Cold Formed Tubes

Assessing "Swaged" Connections in Cold Formed Tubes

Assessing "Swaged" Connections in Cold Formed Tubes

(OP)
I've got a project where they're wanting to used a bunch of these swaged connections. Pretty simple: squish one tube a bit and shove it in the other. What's not so simple is evaluating the capacity of said connections. In particular:

1) How can one assess shear capacity?

2) How can one assess compression capacity?

3) Can compression capacity rely on the geometric interlock or should screws be installed to get the job done instead? I would need a lot of screws for my application. And some related industry offerings lead me to believe that compression capacity can be had without the screws: Link

I have contacted some tube manufacturers as well as the tube steel institute. Thus far, no fruit has ripened however. We've discussed tube in tube moment connections here in the past but that would seem to be a different animal.

What say you?



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: Assessing "Swaged" Connections in Cold Formed Tubes

Other than contact pressure / friction, how are these tubes connected? Thru bolts, welds, or what?

RE: Assessing "Swaged" Connections in Cold Formed Tubes

(OP)

Quote (JP)

Other than contact pressure / friction, how are these tubes connected? Thru bolts, welds, or what?

None of the above. You definitely get some screws in through the side walls for tension applications.

I`m not terribly concerned about shear at the load levels being considered but, still, I`d like to be able to put a number on it. It`s compression that is my main concern. I get the sense that compression may be transferred via the outer tube bearing on the "shoulder" of the inner tube. But, then, that's the crux of my question really. Shoulder, screws, or both? Or would relying on the shoulder result in the screws getting sheared off?

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: Assessing "Swaged" Connections in Cold Formed Tubes

How much compression load are you talkin' about?

RE: Assessing "Swaged" Connections in Cold Formed Tubes

I don't have any special knowledge about this for HSS sections. But, am interested in the responses as it is a good engineering question.

The closest thing that I've seen to this situation is with tapered monopoles for cell towers design per TIA standards. And, the only thing I see in that code is the following from the TIA-G standard:

4.9.7.1 Tubular Pole Structures:
The design length of a slip type splice shall not be less than 1.5 times the inside width of the base of the upper section....


Not very satisfying to me, as I would hope for something a little more technical.

RE: Assessing "Swaged" Connections in Cold Formed Tubes

Nothing beats heavily instrumented destructive lab testing in an approved lab (ICC or university).
In lieu to that, I would sleep better using fasteners alone for axial tension and compression transfer. Ignore the shoulder for compression (except for very load loads - say 200 lbs). Even very high end self-tapping screws are inexpensive and you can get 500 to 700 lbs of ASD shear capacity out of a single #12 screw.
High end swing set connections.

RE: Assessing "Swaged" Connections in Cold Formed Tubes

(OP)
Lots of spots with a few kips. Some brace frames with tens of kips if it's feasible. Don't tease. I'll take whatever you've got, even if it's 15 lbs.

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: Assessing "Swaged" Connections in Cold Formed Tubes

(OP)

Quote (JP)

The design length of a slip type splice shall not be less than 1.5 times the inside width of the base of the upper section....

That's something, thanks.

Quote (ATSE)

Even very high end self-tapping screws...

I don't know much about screws. Could you point me towards one of the "high end" versions?

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: Assessing "Swaged" Connections in Cold Formed Tubes

I don't see an issue with shear, but compression would rely on how well formed the shoulder is.
If there is little to no shoulder then it is just a wedge trying to spread the end of the other tube open.
It would take some testing to validate those numbers.
Personally I would like to see screws through the sides of these.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Assessing "Swaged" Connections in Cold Formed Tubes

Yea, without testing I would only count on the screws. Alpine uses some pretty cool double shear screws for their light gage trusses that have a pretty high capacity.
Dunno, if they are proprietary or not.

RE: Assessing "Swaged" Connections in Cold Formed Tubes

TEK 5's...and should act like a regular sleeve connection.

Dik

RE: Assessing "Swaged" Connections in Cold Formed Tubes

for compression, not aware of any method to analyze it except for testing....it would be a very easy test to set up, by yourself, to get an ultimate compression value.....

RE: Assessing "Swaged" Connections in Cold Formed Tubes

Screws for cold formed steel construction:
1st choice: ITW Buildex TEK (ESR-3223) TEK comes in many different coatings
2nd choice: Simpson Strong-Drive and Quik-Drive X (ESR-3006)

RE: Assessing "Swaged" Connections in Cold Formed Tubes

I feel like if you had to throw a number at it... Maybe...
I feel like the load would concentrate at the corners. So you could check the surface area of just the arc lengths against allowable bearing. Then if we can figure out how to turn the axial force into a lateral force, we could check the buckling/yielding strength of the webs.

Ultimately though I think it has to be testing.

Do you have a link to the moment connection discussion?

EIT
www.HowToEngineer.com

RE: Assessing "Swaged" Connections in Cold Formed Tubes

Pure shear - force at right angles to long (or short) height of the two tubes - or straight "down" into the tabletop in the photo's should be additive. Add all the different steel tubes wall areas together. Alt: If a deformed (squished) tube is a failure in shear - as compared to a complete scissors-like cut, then you'll have to experiment.
Compression forces (if no screwed member!) will crush the two together endwise, but you've already squished (deformed irregularly) the inner tube and forced it into the outer tube just to make the joint. Unfortunately, the point of contact is a nice "wedge" shape as pointed out above, and so you need to test the two several ties to get an average wedging force and deforming force. But really, once deformed, there's nothing to stop the outer from continuing to deform around the inner and slide together. Total deformation will be 1/8's or 1/4's of an inch, not 4's of 1/1000 of an inch.

RE: Assessing "Swaged" Connections in Cold Formed Tubes

Are these splice points going to be placed at locations where buckling could be the failure mode? I'm not sure how you'd determine that capacity.
My gut says if that splice was at the mid-length of a compression member it would buckle at lower load than a non-spliced member but I also wonder if the "doubling" of material at that point would actually help...

Tough one...

RE: Assessing "Swaged" Connections in Cold Formed Tubes

I guess the key thing is how much load required to assemble the two pieces ?

Personally, I wouldn't trust this connection without testing some; or without adding "chicken" screws or blind ("pop") rivets.

another day in paradise, or is paradise one day closer ?

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