Interpretation of BTH-1-2017 re: Lifting Magnets 1

[Pete_K]

This will be cross-posted in Structural Engineering Other Topics.

In BTH-1-2017, Section 3-1.2, there is this language about lifting magnets:

"The loads used in the design of the structural and mechanical components of a lifting magnet shall be derived based on the maximum breakaway force of the magnet. Resolution of these loads into member and connection forces shall be performed by an accepted structural analysis method."

Later, in 6-2.1, (b):

"Lifting magnet suspension devices should meet the lifting magnet manufacturer's recommendations. If any such devices are used during breakaway testing and are not rated for the breakaway force of the lifting magnet, they shall be removable for the purpose of load testing as required by ASME B30.20."

My question is, in the first passage, what is their scope of the term "lifting magnet"? Are they referring to the magnet itself, or is it used to identify the entire lifting device, such as a lifting beam which carries 4 magnets? In the second passage they seem to differentiate the magnet from what suspends it (like a lifting beam?). The implication, or the reason I ask, is that as it relates to the design of the beam, it would have to be designed for the breakaway force of the magnets, as opposed to being designed for the stated rated capacity.

Thanks in advance for any responses.

 

[chicopee]

My interpretations are: First components of the magnets such as each magnetic coil holding device(that secure the coils to the magnet frame) should be design on the maximum break away force. To me that may seem excessive design when you may have several holding devices but don't there could be uneven loading on the magnet as I remember that lifting loads should be spread evenly. Secondly, the lifting beam design should be based on the total maximum break away force of the four magnets as it appears that there may be a significant reduction between the maximum break away force and the manufacturer's rated load; but as prudent as I may be, I would double check on that reduction factor with the manufacturer since I would also include the weight of the magnets and all fittings, wire rope, etc... needed between the beam itself and the magnets. I would also design an extra factor into the beams for shock loading and excessive beam deflection. "...the purpose of load testing as required by ASME B30.20." that requirement may be consistent with OSHA 1910 regulation on load testing of shop fabricated beam so double check.

 

[Pete_K]

Thanks for the response, much appreciated.