Spreader Beam Question

[CTW]

In the paper, "Design and Construction of Lifting Beams" by David T. Ricker, the example only checks the beam for bending. Shouldn't compression also be considered in the design since there is a horizontal force component from the resultant forces on the top lugs?

 

[Qshake]

I'm not familar with the design source, but have seen plently of spreader beams used in various pick configurations.

I would definitely consider the axial load if I could assure myself that it has a load path.

Also please note that many steel sections used in these applications are very robust. Losing a load at any time is unthinkable, but when a beam/girder is part of a building it has some redundancy. While its in the air, that picking rig is the only thing between it and the ironworking crew.

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[AlohaBob]

Yes, axial loads must be considered too. I look at factors of safety associated with rigging. They are on the order of 5.

 

[CTW]

Before I started reading the paper I mentioned in my first post, I had an idea of the forces that would have to be accounted for in the design. Basically design as a beam column and maybe torsion if applicable. But as I read through the paper and followed the example, the author only takes flexure into account when sizing the member. I was hoping some others have read the paper and could explain why the axial force produced by the resultant force on the top two lugs was not considered.

 

[apetr26542]

I've designed some spreaders and I have taken into account the axial force, also consider the axial force is eccentric as it is being applied to the top of the beam through the lugs, not at its centroid like a gravity column. You now have bending, axial compressiona and a Pdelta from the eccentric axial load.

 

[jec67]

A few comments on the design of spreader beams:

-The axial force needs to be accounted for in one's design (as stated by others who have responded to this post)

-Use extreme care when selecting the section to be used for the beam. Give consideration to lateral stability of the beam. I have often used square or round tubes, as the sections tend to be superior to W sections for l/t buckling.

 

[bridgebuster]

CTW,

You may want to pass this question on to the AISC Steel Solutions Center. He's written several AISC publications.

http://www.aisc.org

 

[CTW]

Good idea. I'll do that.