Sleeve Connection Bearing Stress

[maxwolf]

I’m trying to determine the bearing stresses for a sleeve connection. Marks’ Handbook has a number of bear stress formulas, but not for the case where you have a pipe within a pipe with a clearance fit so there’s some kind of small gap between the inner pipe section and the outer. Please see attachment. This gap should cause the bearing stress distribution to maximize at the ends of the lap area when laterally loaded.

The connection is to transfer lateral forces to the base. Set screws would be used to keep the joint from sliding apart. Any suggestions for keeping the set screws from acting as shear studs?

Material is aluminum: 357 for inner pipe; 6061-T6 for outer.
Thanks for any help.

 

[chicopee]

I would not analyze your system the way you are stating. Instead,I would use the beam formulas for bending stress and shear loading.

 

[maxwolf]

Bending stress and shear are below allowable limits assuming load sharing between the two sections. The two sections do not act compositely but act in tandem.

I still need to determine local bearing stress concentrations at each end of the overlap area to verify they are less than allowable.

Thanks.

 

[desertfox]

hi maxwolf

The area's of contact you have at those points will give an infinite stress, what will happen in practice is that local yielding will take place and a slight flattening of the surface will occur to bring the stress down to some finite figure around the yield stress of the material.
I was looking for a book of mine that might give some more help but I can't find it at present but the subject I was looking for was under Hertzian contact or stress.

desertfox

 

[kslee1000]

How many screws in a paticular section? If two screws installed in opposite side, then the gap should be more or less equal on both sides. Instead of shear, you would have local tension/bearing around the holes. If you have 4 screws, the entire setup is quite stable, and stresses at the interface are minimal.

 

[maxwolf]

Herzian stresses is right, but I couldn't find a similar case to this.

I'm using 4 set screws at 90deg intervals around the pole, but I'm not sure how that ensures really equal gap spacing, though I do see how it might help. I think the connection will still have enough play in it to rotate a tiny bit, which I believe will cause the local high bearing stresses at the ends of the lap area(and the local yielding mentioned).

Also, I want to try to avoid having the screws acting as shear studs. They have small sectional areas, and if they yield some, it may be impossible to remove them and change out the pole in the future.

Thanks for the comments.

 

[desertfox]

Hi maxwolf

Yes your right I found my book but there is nothing like your situation.
I would say though if you intend to use screws to hold the inner piece from sliding then these screw ends would take most of the load and your extremities would not necessarily
see these very high bearing stresses, also the screws would become the simple supports for the inner tube when acting as a beam and depending on there position may well affect the bending stressses and deflection.
Does it really matter if the edges of your two mating beams yield a little once they have yielded to reduce the bearing stress they probably won't cause any further problems unless you know something I don't.

desertfox

 

[chicopee]

Maxwolf, you can still use the beam formulae when you you dissimilar cross section if you assume both items to act in tandem. Formulae were developed when you have different moment of inertias on beams.

 

[maxwolf]

Thanks very much for the comments.

 

[KOSMOOOO]

Hello,

How did you solve your issue finaly, did you oriented and disposed your set screws differently.

Kosmoooo