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Elongation of a lifting hook

Elongation of a lifting hook

Elongation of a lifting hook

(OP)
I am using a lifting hook to test embedded mooring eyes which hold down equipment, is there a simple theoretical equation to describe the elastic deformation of the lifting hook?
I am only loading to 5000lbs force, using a Crosby 3.2Ton rated (working load) eye hook. i am neglecting (for now) the other components, as they are grossly oversized for the application.

RE: Elongation of a lifting hook

How will you calibrate your test assembly?

Something has to be assumed, somewhere. If the 3.2 ton rated (7,600 lbf rated) hook is used, then "usual" safety factor is 5x. So 2% yield load (permanent deformation limit) is probably calculated to be 5x the 7600 lbf maximum rated load by the crane hook design team.

So, placing a 5000 lb load on the hook is large, but will not significantly bend the hook. Your wire calbe stretch is much more than that. Your crane beam and crane trolley deformation is probably more - if you are "testing by deformation" your assembly.

RE: Elongation of a lifting hook

As racookpe noted, your Crosby 3.2T hook will likely lift 3.2 x 2 x 5 = 32K with a 2% deformation, with plastic failure about 20%-30% greater.

I've used Crosby products for decades and they are extremely well made. One of the better manufacturers.

RE: Elongation of a lifting hook

How accurate do you need to be? There are 4 ways I can think of to get what you need:

1) Break it down into simple shapes and calculate the deflection of each section
2) Do an FEA analysis
3) Test it
4) See if the manufacturer has that info

I'd rate number 1) as the least accurate. All the other ones are probably pretty accurate.

RE: Elongation of a lifting hook

"I am using a lifting hook to test embedded mooring eye" get a load test guage that you can hook up to the hook and to the mooring eye. I would not bank on a lifting hook for such test for several reasons being first you'll need bench marks in the hook; secondly the hook will spread more so than stretch; thirdly, accuracy will be questionable once measurements are made on the bench marks when hook is under load; fourth, what if the mooring eye is deformed or loosen from embedment under test due to an excessive load from inaccuracy, is the mooring eye to be replaced?

RE: Elongation of a lifting hook

Some basic questions:

- Explain why you are not using a load testing gauge, as suggested above. This is recommended by military test guidelines

- Explain why you must use a hook.... Why wouldn't a load-rated clevis (or other load-rated hardware)work ?

MJCronin
Sr. Process Engineer

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