Lifting Beam Design

The analysis is basic statics and strength-of-materials.
The unsupported length would be the full length of the beam.
Allowable stresses and safety factors come from ASME BTH and corresponding ASME standard (B31.-something).

From my understanding and based off some rigging drawings I see, spreader bars are bought with capacities. You don't really need to design them. Just specify the load they will carry. I don't think the contractor will have the spreader bars fabricated including the lifting lugs attached to it. They'd just buy one of the shelf.

If you need to design it, you may want to look at SWL and 5:1 safety factor.

I have always assumed each end of the beam is a brace point. The ends of the beam can't move lateraly because if they did the load wouldn't be under the hook. The load has to be under the hook.

See ASME b30.1 design of below the hook lifting devices for lifting beam design although the ricker paper is about as straight forward as it gets. Note there is an errata out there on the ricker paper.

delagina:

You are incorrect that all spreaders are bought off the shelf items. Custom spreaders are very commonly engineered items for those who work with/for construction companies.

The ASME standard mentioned by JStephen above (design of below the hook lifting devices) is the go to reference in North America.

Adding to gwynn's comments. A heavy construction Contractor will probably have a random assortment of beams acquired for various reasons over time. A lifting beam will be reverse engineered from an on-hand appropriate member, rather than purchasing a new shape.

Agreed with NS4U, I've always thought of the Ricker paper as the benchmark for straightforward... but ASME BTH isn't too bad either.

Off the shelf vs fabricated is a matter of application. If an appropriate beam can be rented or pulled out of a contractor's yard, that's by far more economical. But sometimes, you need a custom geometry (so the slings below the spreader can be straight) or more capacity than is widely available -- and then a fabricated beam may be required.

Note that there are testing and special fabrication requirements for below-the-hook devices (like lifting beams) that make that more onerous and expensive than a typical construction device.

Regarding the slings above the beam -- for a rented beam, these may be part of the package. But if not, the slings will come in increments of 10' length (in the US), and the length is typically chosen so that the angle between the horizontal beam and the sling are at least 60* to keep the axial load in the beam reasonable. That assumes you have enough hook height with the crane chosen for the lift -- if not, I've seen angles as low as 45* used, but that requires some extra thought. Many beams are rated for different capacities based on the angle of the slings used.

Regarding lateral support -- for a "spreader beam" where the top and bottom slings coincide at the end of the beam, the supported load is assumed to keep the beam from rotating and provide lateral "support". The total spreader beam length is then taken as the unbraced length for LTB.

For a "lifting beam", the bottom slings are cantilevered out some distance from the point where the top slings connect to the beam. That's not necessarily as straightforward for unbraced length, depending on who you talk to. The theory is a little fuzzy here though -- so many beams are fabricated from closed sections to avoid the issue entirely (among other concerns).

To add to the above from both SlideruleEra and Lomarandil,

Closed sections (generally pipe) are common for both spreaders and lifting beams in my experience. If it works with a 12" HP section though, the contractor has a bunch lying in a yard somewhere.

The latest edition of Galambos does deal with cantilevered lifting beams explicitly. If there is another source with opinions that differ from those published there, I would appreciate information on that.

Thanks Gwynn -- I'm always on the lookout for rational explanations for that problem.

Do you mean Galambos in the Stability Design Criteria, or his "Structural Stability of Steel" text?

Other methods I'm aware of are based on some academic papers by Kitipornchai or Helwig and his group at UT Austin. I'll have to take a look to see how those compare to Galambos.

Apologies, I had thought it was in the "Structural Stability of Steel" text by Galambos, as that has been a go to reference for the "other rational methods of analysis" CSA S-16 allows in regards to stability. I also remembered it being laid out in more depth.

The text I should have referenced is "Guide to Stability Design Criteria for Metal Structures," by Zeimian. It only specifically addresses the situation of a lifting beam with a single line at the centre of the lifting beam, and references other works for numerical solutions when dealing with two slings.

I'll have a look for the Kitipornchai and Helwig papers.

Hi

This link might help


“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

I design lifting bars using a safety factor of 5 per OSHA. The lifting lugs require considerable attention. Best to be conservative.

OSHA 1926.251 is fairly specific about load testing being required and about engineering calculations being insufficient. See the two OSHA clarifications below -

I find it odd that OSHA requires a "custom design" spreader beam be proof tested and marked but an unmarked and non tested manufactured lifting beam is A-ok. That's a load of crap.