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calculating circular ring loading

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bsmet95

Mechanical
Aug 16, 2007
114
I must design a rotating device to support a load of 22,000 lb., as shown in the attachment. The device is about 100 inches diameter, is supported on two rollers, and will rotate at 2 RPM for 110 degrees each way. The load is supported on the trapezoid shaped frame within the ring.

The closest formula I can find is from Roark, but it's not very close to what I have. I think I can use the formula, applying the 22,000 lb. load on the outside of the ring (in position C) but the result will be extra conservative.

Might there be anything closer I can use?

Thanks.
 
 http://files.engineering.com/getfile.aspx?folder=4420d579-0667-483a-ba96-5a0b62dacd8c&file=20140624_prelim.pdf
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Sure, your approach is really conservative.
At first sight the position at 0 degrees seems the governing one.
There you have two (almost) horizontal beams supporting together the load; you can take the beams with hinged ends to be fairly conservative. Then you have a circular arch (the bottom part of the circle), with two radial loads at the rollers and supported (non sliding) ends at the lower beam ends (again fairly conservative).
Of course also buckling may be an issue, both in the arch and in the beams when vertically oriented.

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I would analyze the first diagram also, rotate it so the straight beam on the bottom is horizontal, assume it carries all the load. Then use superposition of two of the Roark's cases (one with load from the beam, one with load from the rollers) to find moments, etc. If you want to get more involved, find the horizontal deflection at the load and add forces to make that deflection zero.
 
Bsmet95:
I don’ t like lack of symmetry if I can avoid it. What is forcing in the inner beam framing to be that trapezoidal shape, with the two beams 15̊ off of parallel w.r.t. each other? Can you make any adjustments there? Is that the best choice under these conditions, or might some other condition outweigh that choice? At the very least, I have to look at twice as many conditions in my analysis. Then, you have two choices, you can make the ring very heavy/stiff all around, to take the loads, or you can make the ring lighter and reinforce it through the 110̊ on either side of the center point. Is the load symmetrical, or are there some points where one roller will be loaded more than the other? I’m not suggesting that you not do any engineering, or use any engineering judgement in the process, but be careful that you don’t save 100lbs. of steel and then spend 4000 hours of engineering getting there. The idea that it can’t be done if there isn’t an exact formula covering that case absolutely staggers my imagination, and scares the hell out of me. Reinforce for bottom 220̊ of the ring and the remainder is not needed.
 
Your 22klb radial load is applied thru the trapezoidal beam structure incorporated within the 100" cylinder. And this 22klb radial load is supported by two small diameter rollers equally spaced about the bottom of the 100" cylinder. Offhand I would think the worst case stress condition would be the surface bearing stress at the cylinder OD and roller contacts. But since no details about the roller diameters, the roller spacing, the cylinder wall thickness, the axial length of the rollers or cylinder, or the size/thickness of the trapezoidal beam members was provided, it's hard to say what is more of a concern.
 
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