Design of Below Hook Lifting Devices 3

[SperlingPE]

Good day, is there a specification or design guide for designing below hook lifting devices?
A client has several in house made lifting devices that they would like to get a load rating on.
Our thoughts are to do calc's if possible and apply appropriate safety factors.
So I am trying to find any guidance for this.
Our other thought is to load test the apparatus.
Load the apparatus to an appropriate safety factor times the maximum load that the piece is used to lift.
This may not take the piece to failure, but it will insure that it can lift the intended load safely if it passes the load test.

I have found that lifting devices should be load tested to 125% of their rated load.
But my thought is that you need the rated load first.
Or do you?

 

[WinelandV]

The necessary resources:

ASME B30.20 - Below-the-Hook Lifting Devices, a safety standard Link
ASME BTH-1 - Design of Below-the-Hook Lifting Devices Link

Yes, you should be able to calculate the capacity of the lifting devices. Note that the capacity is dependent on the Service Class, predictability of the loads applied, and whether severe environmental conditions are present.

Hopefully this gets you pointed in the right direction.

 

[SperlingPE]

These lifting devices were made in the shop of our client.
No drawings exist of the devices [same old story, been used for years].
Some of these lend themselves to be able to calc a safe load rating.
Others do not [odd plate shapes, unknown weld sizes, etc.]

 

[JStephen]

There are also marking/ labeling requirements.
If you are not able to confirm welding details/ procedures used, materials of construction, etc., it may not be feasible to rate it after it's built.

 

[SperlingPE]

Without details, that is where the load test comes in.
Does the thought process sound right or do the pieces need to be tested to failure?

 

[dhengr]

SperlingPE:
More and more, these types of equipment are being required to have signage (sp?) showing their cap’y., etc. This is to comply with OSHA and the client’s insurance co. requirements. Your next step is to do a bunch of inspecting of the equip., part and weld sizes, etc., maybe some NDT, to make sure of the condition of the items/parts. You can then make drawings of the equip. and do the calcs. Make some conservative material and weld strength assumptions based on when the lifting equip. was built and the clients knowledge of the items. This all becomes a report/file on that piece of equip. and is a major part of your assigning a cap’y. to the equip. Finally, when you review the links you will see that most of this equip. is tested to 1.25 - 1.5 times the cap’y. of the equip. You will have control over this testing and can watch for any yielding or damage before the test load is reached. You should know about what you think the cap’y. is, and where the limiting details are. And, then there is also an ongoing inspection criteria for the equip. to assure that there has been no detrimental damage which reduces its cap’y.

 

[TehMightyEngineer]

I've done many below the hook designs of unknown and unmarked lifting beams. This can be done but you'll need to be realistic with yourself and the client as to what can be done practically.

To answer your original question, you certainly do need the rated load first. The load test is a double check but does not ensure safety by itself.

If you have multiple items to test then there may be some merit in testing one or two to failure but in my experience this has never been practical or required.

You'll need to be able to calculate the capacities of the lifting beams and rate them based on a rational analysis. Whether this involves high-end detailed analysis (FEA, material testing, radiography, etc.) or involves conservative assumptions (pre A36 steel, assuming poor workmanship, increased safety factors, etc.) is your call. However, at some point the conservative assumptions will reduce the lifting device beyond a useful capacity or your costs to evaluate the devices exceed the cost of replacement with new items or reinforcement of the existing.

Regarding weld sizes and such; you'll need to perform detailed field measurements and evaluations of the existing. At a minimum I would perform a dye penetrant weld inspection of critical welds on any lugs and stiffeners. It can often take many hours to do a proper field evaluation of a large lifting beam.

Finally, when you do load rate it you must consider all possible uses. If side loading, torsion, or other such loading can occur that must be considered. Often I've load rated items for clients who were shocked by how low the load rating was due to one or two unusual conditions. For example, a lifting beam with multiple pick points that had minimal load capacity when loaded up at the extreme ends. It would be worth it to both temper clients expectations and be ready with possible fixes or modifications to increase capacity where practical.

Remember that if these items fail it almost always means a loss of production, a loss of whatever was being lifted, and potentially a loss of life. These are high liability items, tread with care.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[SAIL3]

not knowing the material, welds, history(of abuse) etc....it would seem that fabricating new lifting devices(or off-the-shelf purchase) would be allot more economical and more safe than attempting to rate the existing ones thru analysis or testing....

 

[dik]

Your load factor may be a little light... depends on the use and jurisdiction... for most mining work a load factor of 5 is required and if it's being used in the shaft, a load factor of 10 is required under the Mines Act...

Dik

 

[SperlingPE]

Thanks all for the information.
I have now seen all the devices.
The majority of them are steel tube spreader beams.
There are a few yoke plates.
There are some welded up bolt on lifting devices.
The heaviest load is less than 2 tons.

I am looking for a resource for design of spreader beams.

 

[robyengIT]

hope it can help

 

[rb1957]

The strength of the structure is at least rated load*SF.

The "proof test" to 1.25*rated load is "only" intended to demonstrate that the structure still has at least a rated load capacity.

Presumably your structures have been used with some load, so you could infer what the owner thought was the rated load. But this only stand up if you can "show it good" for the required load (rated*SF).

another day in paradise, or is paradise one day closer ?