Calculate force required to crush a tube 5

[smithtasticness]

I have some tube (see above & ignore the fact that it's bent for now) and I'm trying to find out how I can calculate the force or load it'll take before the tube crushes.

I can't seem to find this anywhere but I think I might be looking in the wrong places. I've found plenty of buckling formula but I'm almost certain that those are either for compressive strength or for buckling along a given length. I think what I need is much simpler, but I'm totally lost on this one. I'm hoping someone here might be able to point me in the right direction.

I'm assuming that realistically I should only need the cross-section properties and material properties to be able to figure it out but at the moment I cannot see the light.

Thanks in advance.

 

[rb1957]

if you want a "proper" loadpath between the bent beam and the box section ... you could put a through bolt.

is the question about the structure or about making the curved tube ?

I suspect that the weakest link is the welds.

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

 

[EdStainless]

Our lifting eyes on spreader beams were always solid bar. A hook can deliver a very localized load, so where a sling would work just fine a hook could lead to collapse and disaster.

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P.E. Metallurgy, consulting work welcomed

 

[r13]

I don't think FEM will help if you don't know the build-in stress due to bending the tube/bar, and the deformation of the shape. but I believe there are available information provided by the manufactures on the web, if you know how to search.

 

[GregLocock]

One ballparky method is to assume it is a failed mechanism with 4 plastic hinges. The moment of plasticity of a section is easy to work out and then you do a work equation.


Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[EdStainless]

I reached out to a former co-worker to mentioned that we did use pipe for some of these. We would use 1.25sch80 pipe (1.660" x 0.191") and then on the inside of the top, the lifting area, we would double it with a saddle made from a split piece of 1.5sch40 that was bent to fit. If you use nominal sizes the ID is too small, but pipe is always made to the thinnest wall allowed. These would be blacksmithed to fit and then welded in and they would extend down into the straight portion a little ways.
This would take our wall from about 0.170" to about 0.300" for some local reinforcement.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[dvd]

Load test a real sample.

If this is a spreader beam it is supposed to be load tested prior to being placed into service.

 

[smithtasticness]

Thanks again everyone for your input on this.

It might be worth mentioning materials at this point. This is stainless steel (316) 60 mm x 5 mm SHS & 1 1/2" SCH 80 pipe. It's a beefier version of its predecessor which was only made from 1" SCH 40 pipe, however, the span has grown to 1200 mm and the weight doubled since then to about 500 kg, hence the upgrade. Oh and the bolt plates are 10 mm.

Old for ref:

I quite like the idea of making the top of the loop solid but I'm still not sure if I'll need too because, in reality, the load isn't that huge.

I'm gonna have to run an inventor FEA aren't I? haha

 

[smithtasticness]

Min. factor of safety of 4.65 which is at the connection between the pads and the box section. This could be an artefact, but regardless, this isn’t bad at all!

 

[LittleInch]

Well 500 kg isn't to be sniffed at and for me the key point is what is the contact area between the lifting device and the pipe - a small hard contact from a hook, metal chain or metal rope or a larger uniform load from a sling or plastic rope?

but yes, 1/1/2" sch 80 - Is this C stl and not stainless? - seems pretty beefy.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[smithtasticness]

Yes, that was my concern and it could easily see a knock as it's industrial equipment.

Not carbon steel no, 316 stainless.

 

[MintJulep]

If you have not already done so, you should review

ASME BTH-1 Design of Below-the-hook Lifting Devices

ASME B30.20 Below-the-hook Lifting Devices

 

[smithtasticness]

Thanks, will take a look.

I've actually done quite a lot of work on lifting lugs and created a pretty comprehensive spreadsheet for that using ASME BTH-1 calcs. This thing is a bit of a different animal though, haha.

 

[LittleInch]

If that's true schedule 80 (5mm) then you actually don't have a lot of force trying to crush the pipe.

the forces are getting distributed all over the place at the top of that triangle and hence I suspect something else will buckle or break before your tube gets crushed.

Let us know when you do the destruct trials what happens....

I assume this will be proof tested to a FOS of 3?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[dgallup]

I don't see a solid bar as a weight penalty. You gain nothing by using a tube. This isn't a space frame where the increased moment of a larger diameter hollow tube improves stiffness.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[smithtasticness]

@littleInch, thanks, will let you know how it goes. We usually only test to 2x but usually do calcs to 5x, go figure...

@dgallup, you're actually not wrong. Might be worth considering. I'll have a ponder over the weekend and come back to it. Cheers.

 

[rb1957]

if you did make the bend from barstock, it'll take a lot more force to bend ... you make need to stretch and bend ?

you'd probably also need to "counterbore" the ends where you weld to the tube.

I think the welds are the weak link, and that tube is more than enough (compared to the welds).

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