Existing hoist u-bolt rating

[bf343]

Hello-

I am analyzing an existing hoist beam and have a question on how to check the u-bolt hoist attachment. In the attached picture you can see the beam cantilever through a concrete wall and at the left end of the beam is a 3/4" u-bolt through both flanges. Both of the existing "hoists" in the picture will be removed and one hoist will be attached to the existing u-bolt with a hook very similar to what is shown in the picture.

So I am thinking I need to check the u-colt for tension, which has two legs, and shear. However for the shear, is it double shear or single shear? Since the new hoist will attach with a hook, it makes me wonder if it would be single or double shear. I am leaning toward single shear just to be conservative but would appreciate some feedback.
Thanks

 

[CANPRO]

bf343, I think double shear is appropriate. The only way the u-bolt can fail in shear, on a single plane, is if all of the tension is placed in a single leg. The single plane failure you're picturing is probably a failure due to bending. Depending on the proportions of the u-bolt and the hook, this may or may not be an issue. See attached sketch for clarification.

 

[JedClampett]

I don't think a U-bolt is a standard attachement for a Hoist Hook. I can see the one in your picture has already deformed due to forces parallel to the beam. There's all kind of complicated and wonderful stresses in that simple U-bolt.
I would consider a pin and a welding eye (

http://www.anvilintl.com/products/p...attachments/66-figure-welded-beam-attachment)

with a published capacity.

 

[bf343]

CANPRO-
Thanks for the feedback. Yes, the bending of the u-bolt is a concern, and when I checked it, it is what governs the capacity.

JedClampett-
I agree that a u-bolt is not an ideal hoist attachment, however they are sadly everywhere at most grain elevators in our area. Our client wants a rating for what is existing and then if that is too low, we would look at repairs.

Thanks

 

[dhengr]

Bf343:
Some questions for you to answer in the process of evaluating this U-bolt lifting device.... The mat’rl. spec./strength of the U-bolt material; dimensions of the entire system, and some good well proportioned sketches of it; beam size, dimensions, back span length and attachment to the structure, bearing stresses and conditions on the conc. wall, mat’rl. spec. for beam; top flg. bending under the U-bolt nuts and over the beam web; what is it used to lift, and its size and wt. The analysis of the U-bolt itself, involves some bending, shear and axial stresses, and combinations of these at various locations. Take a look at the design of hooks, chain links, curved/bent beams, Hertz bearing stresses, pin plates, as in lifting lugs, and ASME below the hook lifting equipment. Then, add some safety factor for rust, deterioration, your own uncertainty, etc. The large hook seems to fit the U-bolt pretty well, and that’s important for the bending and bearing stress issues. That system may be o.k. for your final application, but that isn’t the way I would detail it, if I could start over by removing the U-bolt, and modifying the tip of the canti. bm.

 

[chicopee]

For an initial "feel" for the strength of this "U" bolt, check out manufacturers' catalogs on line. Definitely, while this hoist may have had several years of successful service is a Rube Goldberg contraption.