Rigging with a hook through a hole in a plate

[ALREMAN]

I have a lifting application that I am helping with. I have been taught that in general it is bad practice to rig something using a hook in a hole drilled through a plate. This is due to the large contact stresses at the edges of the hole. A better alternative is using a shackle so that you have a round pin through the round hole. However, when discussing this with a co-worker, he found several beam trolleys with a connection point that is no more than a hole through a flat plate. See the attached image. This tells me that maybe this isn't as bad a practice as I thought. Are there any restrictions to joining a load this way? Any thoughts?

 

[Ron]

A hook through a plate hole is a common lifting mechanism. Yes, the stresses are high, but that should be designed. I have done this many times with large tanks (50 feet long, 12 feet in diameter) and have not had a failure through the plate.

 

[ALREMAN]

Thanks for the speedy reply Ron! Do you have any suggestions on how to design this connection type? Do you just assume that the hole is going to deform to the required geometry and then size the pin and plate thickness based on shear?

 

[BAretired]

Don't we have the same condition when using a bolt through a plate with minimum loaded edge distance? If your loaded edge distance satisfies the code, you should be okay. For a lifting operation, you should be using a higher safety factor than normal, probably in the order of four or five.

BA

 

[Ron]

Agree with BAretired. If you are in the US, check the OSHA requirements. The safety factor is in the range noted by BAretired.

 

[ALREMAN]

BAretired, thanks for the reply. The bolt through the plate situation would be similar to using a shackle instead of a hook. Since the hook is curved, it will only contact the hole at two point at either end of the hole. I normally use a safety factor of 5 for lifting applications. I think what I'm hearing is that if you design the pin and the plate material to withstand the shear stresses, the safety factor takes care of any concerns due to bearing stress. Would there be a situation where the pin may fail due to the high contact stresses and not shear? It seems like there should be some way to analyze the stress on the pin given this type of geometry. Do you have any references?

Thanks!

 

[KootK]

One of the key differences between a lug and a bolt hole is that the "pin" for a lug is much smaller relative to the hole, resulting in greater stress concentration. That said, a shackle pin also cannot be expected to produce uniform bearing stress on the lug. The lifting will usually be done at some angle relative to plumb (15 deg, 30 deg etc). In such cases, the shackle pin will be cockeyed with respect to the lug and you'll again get the high contact stresses that you're worried about. In summary, I wouldn't sweat this. Use a big factor of safety and a ductile steel, and sleep easy.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[dhengr]

ALREMAN:
Take a look at the shapes and dimensions of most lifting hooks. They are kinda pear shaped over a good share of their body, with the large wearing area on the inside or bearing surface of the hook. Then, they will often have an even wider, shaped, flange area on the inside surface too. This gives them a fairly substantial and generous radiused bearing surface for wire rope or to mate with the hole in a lifting lug. The hole in the lifting lug generally must be bigger when a hook is used, to accept the full shape and body of the hook. It might also have doubler pls. (doughnuts, cheek pls.) on either side to thicken the lifting lug, and it is likely shaped (mating shape) to match the general shape of a hook. The thing that OSHA doesn’t like about this lifting arrangement is that it is often difficult to use a hook with a safety latch with a lifting lug pl. A lifting hook would fit quite nicely on the trolley that you show and load its lifting eye (suspension pl.) in a better fashion than a clevis or clevis pin would. I believe the proof load for most hooks is at least 2 w.r.t. their rated load and the design FoS is higher than that. Note also that when you design a lifting lug eye for use with a clevis pin in bearing, the pin dia. is best when it is only slightly smaller than the pl. hole dia.; and the thickness of the lifting lug pl. should be only slightly smaller than the width opening of the clevis. This matching thickness forces the use of the appropriate sized clevis; one with a smaller pin won’t fit over the doubler pls. No matter what lifting means you use, the lifting line, chain, wire rope, whatever, should not deviate from the plane of the lifting lug pl. by very much. Without special design attention, the lifting pl. is not intended to be loaded out of plane.

 

[jreit]

Typically, for any sort of lifting application we use a SF of 5 or higher just like you mentioned.
You can use ASTM BTH-1-2008 or 2005 as the standard US reference for a full-fledged design.

 

[TehMightyEngineer]

Just out of curiosity; why can't you just use a shackle or a swivel lifting eye? I agree 100% with the above and have seen hooks used directly on scrap metal cut out from tanks during repairs and not worried about it, but 99% of the time the only benefit I see to using a hook directly on a part is slightly less rigging time.

Professional and Structural Engineer (ME, NH)
American Concrete Industries

http://www.americanconcrete.com

 

[SAIL3]

the example shown by the OP was probably load tested....I would not recommend using a hook for the reasons stated unless load tested....I am not aware of any theoretical analysis to design a lug with a hook...I also do what dhengr recommended in designing the lug to fit only a certain size shackle...