Lifting Lugs design for Annular Plate weight about 3.5 tonne 1

[jones1234]

Hi all,

There is a circular plate with 4000 mm OD, 2500 mm ID and 400 mm height. We need to design a lifting lug for this plate. Consider structural steel as plate material.

How the weight of plate should be considered which will apply on lugs ? Should the weight be considered at COG and then bending moment will apply on lugs ?

Could any of you please help me to understand where should lug be welded and its position ?? I was thinking of placing 2 lugs on plate surface 180° apart but at which diameter that I needed to figure out.
If you guys could help in understanding which loads will apply on lugs while doing vertical lifting, that will be a great help.

Thanks,
Jones

 

[oldestguy]

Review this subject as discussed elsewhere for failure of lifting lugs on boat storage facilities. There stress concentration at bends caused early failure at stresses well below the typical yield point for steel. Your lugs may have stress concentration that causes failure well below yield.
Look under "welding, bonding, etc." However, they waste a lot of time and this subject didn't get discussed until brought up the subject.

 

[HTURKAK]

Name of the thread ( Lifting Lugs design for Annular Plate weight about 3.5 tonne )

W=pi*(2**2-1.25**2)*0.4*7.85= 24 tons..

Check ur dimensions again..

 

[JLNJ]

The weight will always be applied at the center of gravity, just like god intended it. Whether or not there is moment to account for where the lugs attach to the plate depends on the orientation.

I presume the plate oriented flat to the ground when it’s lifted. It may tip just a little or need some guidance during the lift. Is this acceptable? What is the material? It seems like it should be pretty stiff and strong at 400 mm thick.

 

[jones1234]

@HTURKAK - Sorry for not specifying earlier, actually the whole plate is not made of Stainless steel... Plate thickness is 20 mm. There is different material is filled in void area which I'm not aware of to be honest. I believe during lifting we're only concerned about outer material and total weight, which is about 4 tonne.

 

[r13]

jones1234,

Yes, your proposed lifting method is correct. Place two lugs, one each centered on the end leg, and symmetric about the COG, so each takes one half of the lift weight in tension. The stress in the lifted plate should be checked as a curved beam.

 

[dhengr]

Jones1234:
Let’s see here…, at 13’ o.d., 8.2’ i.d. and 15.75” thick, weighing about 8000 lbs., that’s not a particularly large load, but it is still a fairly precarious load to be lifting from only two points. We know where the c.g. should be (at the center of the ring), but we can’t be absolutely sure that it will be there. And, on a 6.5’ lever arm, it wouldn’t take to many lbs. out at the o.d. to cause that ring to start to roll about the plane of two lifting lugs. That’s not uncontrollable, but it is mighty frightening when it is an unexpected happening. I would be inclined to pick that ring from three or four points so as to control its stability. It might swing or lean a little to bring the c.g. under the lifting hook, but this will be under some control. This will reduce the bending and torsional stressing in the ring during lifting too.

We really need to know much more about that ring to comment further. What is its real weight and makeup? What position will it be lifted from, and what orientation will it need to be in when it is put down, or put into final position? It could be lifted from one point on its edge, if that suited its final positioning. To determine the bending in the lifting lugs, you have to look at their orientation w.r.t. the lifting slings throughout the entire lifting operation. Many times you try to orient the lifting lugs so they are in approx. the same plane as their sling, so a to minimize their out-of-plane bending.

 

[r13]

Since the plate is quite thin for the span, handle it carefully to avoid damage during lifting. Temporary stiffeners, or lifting cage, may be required if the plate is too flexible.