Bearing Stress on a Shackle to Shackle connection
Bearing Stress on a Shackle to Shackle connection
(OP)
Hi all,
I am after a little help. I have been asked from a client to assess the bearing stress on a shackle which has another shackle directly attached perpendicular to this, i.e. one cylinder crossing another, with a load less than the SWL of the shackle. Normally I would approach this using Hertzian stress or using Roark's however using these methods I obtain a stress 13 times higher than yield.
Obviously the shackle does not yield under this loading, so I am guessing either the methodology is incorrect or my limit of 2 x yield stress in bearing is incorrect. I am no shackle expert, so are there any other methods anyone can think of?
I am after a little help. I have been asked from a client to assess the bearing stress on a shackle which has another shackle directly attached perpendicular to this, i.e. one cylinder crossing another, with a load less than the SWL of the shackle. Normally I would approach this using Hertzian stress or using Roark's however using these methods I obtain a stress 13 times higher than yield.
Obviously the shackle does not yield under this loading, so I am guessing either the methodology is incorrect or my limit of 2 x yield stress in bearing is incorrect. I am no shackle expert, so are there any other methods anyone can think of?






RE: Bearing Stress on a Shackle to Shackle connection
Bearing stress should be considered
https://en.wikipedia.org/wiki/Contact_mechanics
RE: Bearing Stress on a Shackle to Shackle connection
Perhaps the customer could tolerate linking the shackles with a double padeye, sort of like a big roller chain link?
Mike Halloran
Pembroke Pines, FL, USA
RE: Bearing Stress on a Shackle to Shackle connection
The only rule that must be followed is that shackles in series should be linked bow-on-bow or bow-on-pin, but NEVER pin-on-pin.
RE: Bearing Stress on a Shackle to Shackle connection
My understanding is that for Crosby shackles at least, even pin-on-pin is acceptable as long as the pins are actually bearing on each other (the shackles aren't being bound up at the ears).
RE: Bearing Stress on a Shackle to Shackle connection
RE: Bearing Stress on a Shackle to Shackle connection
Also, in my general practice, I try to never exceed SWL/2. Obviously SWL can be approached safely, but in my industry I often deal with the 'that looks strong enough' mentality from millwrights, so I use that rule of thumb to try to spec in an additional layer of safety against stupidity.
In other words, consider going up a shackle size or two, if you can.
RE: Bearing Stress on a Shackle to Shackle connection
The localized bearing stress in a situation like yours is well confined by the surrounding, non-yielding material; so, it is typically allowed (tolerated) that it be much higher than our normal allowable bearing stresses would be. The plastic deformation occurs, the bearing area grows until there is localized compatibility and equilibrium, and it really can’t/won’t go any further because of the larger volume of material containing it. It works. As mentioned above, the initial contact stress is essentially infinite (as your calcs. tend to indicate) and small mating bearing areas are formed and grow in size which quickly brings the bearing stress down to a reasonable level. This is indeed a Hertz contact/bearing stress problem, and you should look at it from that standpoint. The other comments above are to suggest that you want the shackles to act as they were intended to act, and in the line they were intended to act on. JgKRI’s 30JUN16, 16:04 advice is particularly good. I would add that pin-on-pin contact puts the pins in too much bending, and they are primarily intended to work in shear (double shear). Then, there is also the chance of some shock loading if one pin slides on the other pin as loading occurs. The dia. and size of the shackle body are designed to tolerate a bit of this type abuse (deformation and wear), while the pins are not.
Edit: You could cut a piece of heavy walled pipe to fit over the pin, pipe i.d. slightly larger than pin dia., with its length to fit within the two sides of the shackle. This protects the pin from damage, distributes the master link point load on the pin and with the pipe o.d. being larger improves the dia. variables btwn. the pin/pipe and the master link in the Hertz stress calcs.
RE: Bearing Stress on a Shackle to Shackle connection
-5^2 = -25
http://www.eng-tips.com/supportus.cfm
RE: Bearing Stress on a Shackle to Shackle connection
RE: Bearing Stress on a Shackle to Shackle connection
RE: Bearing Stress on a Shackle to Shackle connection
The above link from a manufacturer explains the limitations of linking shackles. It is allowed but under certain conditions. A call to the manufacturer of the shackles you are using may be helpful as well as they may have literature on testing linked shackles.
RE: Bearing Stress on a Shackle to Shackle connection