Thickness of Lifting Lug

[knandwana]

Hi All :

As described in "Design and Construction of Lifting Beams" by David T. Ricker the minimum lug thickness should be 0.5in, in order to prevent dishing.

However for my project :

1) Weight of the equipment to be lifted is only 3000 lbs.
2) 4 lifting lugs will be used.
3) I can only go upto 3/8in lug thickness. What should I do ?

What formula did David T. Ricker used to reach to the conclusion of 0.5in ?

Thanks,
Kapil
Structural Engg.,EWI

 

[CTW]

It's a suggested minimum, but remember that this publication covers lifting beams. Dishing is going to be more critical in a lifting beam or application where repeated lifts are being made. If your just moving and setting equipment, then I don't think the 1/2" minimum would apply. In non-lifting beam applications, I've used 3/8" plate before.

 

[DWHA]

I am not sure exactly what you are describing by a "lug" thickness, but what I have done in the past for picking eyes that contractors attach shackles through is this. I use AISC code check for bearing at bolt holes. I also check block shear for the area. I typically & conservatively take the load as a live load, then add a 1.3 factor to it for any impact. I hope this helps.

 

[Bagman2524]

I agree with both posts above. The 1/2" min. sounds like a particular loading case which doesn't apply to your case. See AISC 9th ed. section D3.

 

[DRC1]

I would be a litle concerned about a 3/8 inch plate, as a lot of unintended forces usually get absorbed by lifting lugs. The paper is an excelent reference. However, to incease the stiffness of the plate and the bending resitance of the weld I would weld a trapaziodal stiffener at each end at right angles to the lug. It could go to the top of the lifting lug. This should give you a very secure connection for a small additional cost.

 

[miecz]

I would guess that Dave's 1/2 inch requirement was not based on a formula, but on years of hands on experience with lifting devices.

AISC's provisions for lugs were originally developed in ASCE Transaction Paper No. 2023 by Bruce G. Johnston, "Pin-Connected Plate Links"published in 1938. This paper presented some sophisticated formulas to prevent failure, but these formulas never made it into the code.

The approach published in the AISC specifications until the 9th edition included a cryptic provision for dishing. The approach was in Article D3 of the 9th Edition, and was to size a lug for fracture at the side of the pin hole at 0.45 Fy, and then provide a higher factor of safety for the other potential failure modes: bearing, failure beyond the pin hole, and dishing of the entire plate.

The geometrical requirements of part 2 of D3 prevented the other failure modes, but didn't explain things clearly.

The requirement that "the edge of the member or element shall not exceed 4 times the thickness at the pin hole" was meant to prevent dishing of thin lugs. It might have been clearer if it had been stated the other way: e.g., the thickness of the plate shall not be less than 1/4 the distance from the edge of the pin hole to the edge of the member.

This requirement can result in some pretty thin lugs, but was not meant specifically for construction conditions. Curiously, the dishing criteria seems to have been left out of later editions of the AISC manual.

 

[topsisu]

The design of lifting lugs and related devices is covered in ASME BTH-1 - 2005 "Design of Below-the-Hook Lifting Devices". This standard includes variable safety factors based on usage. Only about $50 - recommended.

 

[WillisV]

Agree with topsisu - ASME BTH-1 should be used for lifting lugs (its actually in a 2008 edition now). The formulas for pin connections in AISC are intended for permanent pin connections - not lifting/rigging.