Lifting Beam / Spreader Bar Design Considerations 1

[fjacq]

I find myself designing a variety of in house lifting beams and spreader bars for lifting plates and structural shapes for material handling purposes. Currently I am working on a 100' long lifting beam with a working load capacity to 40 tons, two lift points above the beam and 5 sling points under the beam. I want to develop a comprehensive design protocol to standardize design loads, weld sizing, and fabrication requirements. My question is in several parts:

1) Beyond ASME B30:20, are there any other standards or regulations that govern here? (U.S. Specific is fine, but a worldwide list would be interesting)

2) (Basic beam calculations for bending and shear stresses, compressive bucking, and deflection I've got covered, but what other loads might I need to consider for safe handling, stability, etc.)

3) What other issues outside of design and fabrication might I be missing?

Any advice or direction to existing literature is greatly appreciated! Thanks!

Fred J.
EIT, American Bridge Manufacturing

 

[mrMikee]

I've been told that OSHA requires a 3 to 1 factor of safety to yield and a 5 to 1 factor of safety to ultimate, but I don't have any details with me now. I designed lifting devices big and small for years basically using this as my guide. I too will be interested in more technical data regarding this topic.

Regards,
-Mike

 

[ornerynorsk]

You definitely want a great margin of safety factor, especially considering potential shift/overload/sling failure of a dynamic lifting structure. 5:1 safety factor is not unreasonable considering the weight that you are dealing with.

 

[ccw]

Hi fjacq,
You probably need criteria for clevis or eye design and attachment, including eye/pin bearing, tear out, bending, etc.

Develop a list of preferred materials for use in construction ie. field weldable, ductile, readily available, economical, etc. Develop a good clean and paint spec. and standarized stenciling for posting load ratings, mfg. history, loading diagrams, etc.

Establish and document proof loading and inspection/maintenance criteria and procedures that are suitable to everyone. Make sure all of this is conveyed on the design and mfg. drawings and spec.s

Also, the larger lifting fixtures need provisions designed in for moving and storing such items out from under the crane way hook coverage when not in use. This can be a big deal in busy mfg. bays. Don't invite fork truck operators to jab and stab at your lifting fixtures with their rigs trying to pick them up or move them around.

If you can talk your boss into it, sign up for the nationally recognized 40 hour master riggers course. It will help familiarize and sensitise you with things from the lifting fixture user's point of view, also with commercial rigging hardware that you will need.

 

[mrMikee]

fjacq,

One suggestion I have is to make sure your assumptions are not too idealized. For example you indicate that you will have 5 sling points. This might mean 8 tons on each point but maybe it will be 20 tons on two points, and so on. While this possibility is fairly obvious, sometimes possible ways to overload lifting equipment can be easily overlooked.

-Mike

 

[arto]

Mil Std-209 has some good stuff on lifting

 

[fjacq]

Thanks all for your responses to date.

MrMikee - I typically design these units to a 3:1 yield SF, but would like to know the specific OSHA chapter governing here - do you have that reference?

ccw - it sounds as if you've done a few of these before - do you have any pubslished standards you could refere me to?

arto - Thanks for the reference, I will look into it.

As for design assumptions, the initial beam calculations are based on fully loaded on 2 of the five lifting eyes. The eyes themselves are designed for full loading on a single eye. My most serious concerns right now are horizontal rigidity of the beam during lift, how to identify risk and consequence of possible load shifts, and any regulatory compliance I may be overlooking.

Any how, if anyone comes up with anything else, please post it. Thanks again!!!

Fred J.

 

[TomBarsh]

hi Fred,

You might be overlooking the most valuable source of information...your own company!

American Bridge has been around for such a long long time and has performed many large projects of innovative and historical importance. Surely there must be company technical standards on lifting procedures including design of spreader beams and lugs, etc. Speak with some of the old hands and find out where those old files are, either as company references or in old project files. Then study up and let us know what you learned!

Tom

 

[mrMikee]

fjacq,

I have been unable to find my file containing the article about lifting factors of safety that I was thinking about. It was not something directly out of OSHA but instead a technical article from an engineering magazine, if I remember correctly. If and when I run across this I will post it.

-Mike

 

[TomBarsh]

The AISC Engineering Journal, Fourth Quarter 1991, has a 10 page article by David Ricker titled "Design and Construction of Lifting Beams". The article addresses design of the spreader bar in addition to some issues related to attached lugs for shackles.