Point load on pipe wall exterior

[htfptm]

By what method could a radial load on a pipe, towards the pipe center, be modeled to determine stress in the pipe? Specifically, this is in a jib crane using cam rollers on the pipe as the support for the jib.

 

[ishvaaag]

Initially, as a point load. If more is known, a distributed pattern of load in a line or portion of the surface may be used for more detail. The model must reflect realistically the geometry and the restraints ... I don't know if this serves as a start answer for your question.

 

[dhengr]

Htfptm:
I do know what a jib crane is. But, only you know ‘ Specifically’ what you are looking at. Imagine the number of different arrangement drawings that could be made meeting your description. They say a picture is worth a thousand words, and you are 959 words short, or one sketch short.

What is the pipe dia. and its wall thickness? What size and how many cam rollers, and at what loads? I suspect bearing stress (Hertz stress) and wear btwn. the cam roller and the pipe and alignment btwn. them may be as big an issue as some general point loading stress, once other details are given due attention. You may want a stiffener ring on the pipe at this location and a hardened running surface or bar/track. Timoshenko and Roark will likely have something that addresses your exact question, the problem will be the boundary conditions for your problem, as Ishvaaag suggests.

 

[csd72]

AISC design of hollow section connections covers this.

 

[Gumpmaster]

Like dhengr, Roark covers this in Table 13.2 (loads on thin walled cylindrical shells) of the 7th edition (Table numbers may vary by edition). You may want to look at either case 9 or case 15.

 

[htfptm]

Thanks for the replies, guys. Here's some better info:

6" sch 80 pipe (.430 wall). (2) cam rollers, 1 1/4" diameter x 3/4" length mounted at 90 degree separation along pipe circumerence. Max load per roller of 2,600 lb towards pipe center. Rollers are 20" below the top of pipe (nearest gusseted end of pipe).

 

[ishvaaag]

I would do an initial assessment with the loads as point load and if available an impact factor typical for the kind of gear. Then I would assume only 2 rollers loading the pipe, first contiguous, then opposed. This would give me a feeling of where we are in terms of stresses. And I would build from there to more accurate pattern of loading, stress concentration, fatigue etc preferably in the scope of some crane code.

 

[ishvaaag]

If the non-loaded rollers may come in contact with the deformed pipe as to give a reaction, what is likely the case, then I would provide reactions there for the described hypotheses.