Below-the-Hook Devices & Lift Hook Contact Stresses

[benzflieger]

I am designing a spreader bar to lift 15,000lbs with a safety factor of 3 when considering yield stress. This spreader bar will be made from a laser cut piece of 1" thick A36 steel plate. The customer's crane has a typical 8~10 ton Crosby swivel hook, and I have located an elongated oval hole in the plate for this hook to engage the plate.

I am using ASME BTH-1-2008 "Design of Below-the-Hook Lifting Deveices" as well as ASME B30.20-2006 as my design standards. My problem is that nowhere in these standards is there any mention of how to handle the contact stresses between a curved hook and the hole thru my plate. "Common sense" and past experience/observation tells me that the 1" plate is more than capable of handling the load and that the plate will locally deform at the two "point contact" locations until the contact pressure applied by the hooks to the plate is resulting in something around the yield stress level. Be bottom line is that the plate will be "OK".

Does anyone know of something authoritative I can point to in my engineering calculation write-up that backs up my claim that the hook contact stress as described is OK. If I need to treat the Hook-to-plate contact as a "pinned connection" I can do this, but because of the formal write-up required, I need to point to something that says this assumption/simplification is acceptable by industry, etc. (By the way simply putting a shackle in between the hook and the plate to give me a true pinned connection is not acceptable because of the customer's application)

Any ideas would be helpful. (Normally I don't try to get so "wrapped around the axle" this much, there's no getting away from it this time. )

 

[chicopee]

What we did in our heavy steel fabrication plant was to increase the widths at the eyes of the lifting beam by fillet welding additional 1" thick plates on both sides of the eyes.
While it was more than required as you pointed out in your statement "...Common sense and past experience/observation tells me that the 1" plate is more than capable of handling the load... " after a period of constant use, the lifting beam eyes will show metal compaction and wear.

 

[jte]

You might want to consult with the author of the following paper:

http://asmedl.aip.org/vsearch/servl...s=ASMECP&key=DISPLAY&docID=1&page=1&chapter=0

He certainly has a handle on this issue and is very competent in explaining challenging technical issues in a way that both engineers and non-engineers can comprehend.

jt

 

[chicopee]

Formulae for contact stresses between two surfaces s/b extensively presented in ME handbooks such as Kent "Design and Production". In your case, contact stresses would be between a cylinder such as a shackle pin thru the eyelet and the internal concave surface presented by the eyelet.