When it comes to rigging hardware, is one choice greater than another? In what situations are shackles not the right option? If your only readily available lifting beam would place angular forces on the lifting point, are eye bolts viable? In selecting hardware for your lift, the project or lift plan tend to dictate the best option.
Many times, a load will come with the lifting points already determined or attached to a shipping base or directly incorporated in the design of the unit. This can come in the form of welded lifting lugs, permanent shackles that raise out from the base or a variety of other fixed lifting points. In these cases, your lifting point has already been decided so your job is to just get the right setup to perform the lift. For this post, we are looking at the instances when the load has no set lifting points or simply comes with holes from which you are responsible for finding the best hardware option.
Take, for example, a 32,000-pound generator. We have seen these on job sites where there are eye bolts attached on a shipping base, lifting holes left in a base designed for a shackle and even some that would require a swivel hoist ring just to allow the load to be lifted with a single beam since the positioning of the holes would not line up properly for anything other than a vertical pick.
While this is a narrow example, let’s look through each of the above-mentioned options and see when you would choose each of them and why. To start, we will take a look at the limitations for each.
Shackles require an opening on the unit that is specifically meant to accommodate a shackle. Otherwise, additional hardware is required, which we will cover down below. In other words, if all you have available on your load is a drilled hole, simply adding a shackle would not be an option. That said, however, shackles allow for rigging to spread up to 120-degrees from the horizontal without losing any rated capacity. This means that our generator with four pick points can be safely lifted with a single spreader while using as small as a 4.75T shackle (assuming a perfectly spaced center of gravity). Shackles are generally the preferred rigging hardware selection given the versatility and strength at most angles.
Forged eye bolts, when speaking in rigging terms, should ideally only ever consist of shouldered eye bolts. The shoulder provides added stability that allows angular loading – albeit at drastically reduced capacity – whereas a non-shouldered eye bolt would simply bend until sheared off. Before getting into the capacity reductions, eye bolts require more care to ensure they are being utilized properly. With a shouldered eye bolt, the shoulder must be fully seated onto the surface to accommodate any angular load. It’s also important to remember that a fully seated eye bolt needs to be threaded into the surface at least 1.5 times the diameter of the bolt. Also of note, eye bolts are also generally used in conjunction with shackles to perform the lift
With that out of the way, the flaw in eye bolt use lies in the reduction based on the angular forces. While ANSI/ASME has two separate guidelines in B18.15 and B30.26, the manufacturer is your best resource for knowing the actual working load limit (WLL) for your application. Absent that information, however, your safest practice is to run with the capacity reductions listed in ANSI/ASME 30.26 in which they show that an eye bolt retains 100% capacity up to five degrees from the vertical.
As you can see in their graphic, anything between five degrees and 15-degrees from the vertical is only rated for 55-percent capacity and anything beyond 15-degrees from the vertical is reduced to only 25-percent of the rated load. What this means is that for the same lift, where a 4.75T shackle is sufficient to handle the load, you would need to calculate the angle of the lift to determine the size eye bolt. Assuming the same single beam pick, the expected angle will most likely fall above 15-degrees, so you would then need, at minimum, a 2” eye bolt – rated for 32,500 pounds in a vertical lift – to pair with your shackle as the WLL would now be 8,125 pounds or 4.06 tons.
Swivel Hoist Ring
Enter the swivel hoist ring. Swivel hoist rings operate in a similar fashion to eye bolts but differentiate themselves in that the hardware provides 360-degrees of rotation and retains its rated capacity at any angle. In a situation where an eye bolt would be required to perform the lift, swivel hoist rings provide a safe, suitable alternative that allows for angular loading without having to worry about the reduction.
To give a better idea, while referring back to the generator, while it would require a 2” or larger eye bolt to perform the lift, using a swivel hoist ring would require only a 1” bolt size that would carry a 10,000-pound WLL and safely fulfill the requirements of the lift.
As you can see, each of the above hardware choices can be used in one way or another, but your load ultimately determines which option you go with. The best choice from above would be to utilize a shackle if possible, but any of the above combinations can get the job done.