Bolt shear in overhead lifting application

[Chronik]

Hi,

I am currently designing a hook that is going to be attached to a lifting beam we just purchased. The beam is rated for 2000 pounds, and we have to lift up to 600 pounds total (2 hooks, therefore 300 pounds per hook).

Attached is a drawing of the current design.

Because of the thickness of the hook, there is a gap between the bracket that attaches the hook and the bracket that is welded at the end of the beam.

I know how to calculate the shear in the 3-bolts section of the system, but how do i take into consideration the 1/8'' gap there is on both ends of the beam bracket.

The hole in the beam's bracket allows a 3/8'' screw to go thru. I was thinking of using a 3/8'' shoulder bolt as shown on the drawing, and two 1/8 (or a little less, it has to be able to swivel a bit) steel spacers to fill the gaps.

**Please note that you do not see the full beam in the drawing. Only the end plate of the beam which the hook is attached to is shown.

Thank you for your time.

 

[Cockroach]

An interesting problem, and a classical structural engineering problem. There are textbooks that deal with combined loading on bolted connections, I would be surprised if you couldn't find one very similar to yours.

You need to look at the bolting as a patterned system and find the loading through each bolt, they do not carry identical loads. That is obvious from just the statics. You also need to determine "maximum lifting acceleration" in order to do the analysis under worst case. Remember that acceleration is like gravity, the division of the two numbers would give you a weight multiplier for your analysis.

As far as the gap, I would over bore the holes slightly and sleeve the bolts to the required length. Remember to leave a little short so that when doing the make-up torque, the bolts will squeeze the piece slightly and you can achieve the recommended make-up.

An interesting design, the lack of geometric detail leaves much to the imagination and impossible to complete the mathematical model that details your situation. But good luck with it.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[osoloco]

While spacers will not alter the bending stress in the shoulder bolt, they will keep the load centered. Without the spacers the load WILL shift to one side or the other. This is not the problem that is being analyzed.
I would consider reaming the holes in the side plates if you are very concerned about localized stresses.
Consider a larger diameter bolt... I realize that the fun is in the details... but a larger diameter bolt will usually solve the problem.

 

[chicopee]

"The hole in the beam's bracket allows a 3/8'' screw to go thru...." With that statement, you are flirting with mishap.

You have three (3/8)bolts on the end of the lifting hook and you want to use only one 3/8" bolt on the link bolted to the hook as shown on your original drawing. Something does not jive.

 

[izax1]

Not only is there 3 bolts vs 1 to take the same load, but the design with the one bolt wil also introduce bending, which avoid in the 3 bolted connection. Can you increase the lug on the crane end to give room for more bolts?

Also, be careful with swithcing to a more refined methods like FEM. I can not see how a FE analysis would give you more information than you can get with a simple hand calculation. This is a simple geometry. FEM will help you if you have a complex 3D geometry. The challenge of interpreting complex FE results on a simple geometry is not straight forward.

(Unless you are in research and not in the business of solving practical problems.)

 

[iceblink]

Can anyone point me to a European counterpart of the ASME BTH-1 spec? Preferably British, but other EU will also do.

I'm looking into a lifting eye that is bolted to a machine, where the bolts provide a friction transfer of the load.

In ASME BTH-1 the maximum allowable load is n*0.26*A*Fu / (1.2*Nd) where n is number of bolts, A is bolt section area, Fu is ultimate allowable stress of the clamped parts, and Nd is the safety factor. I don't understand where the 0.26 originates from. (I expected it to be 0.24/0.36/0.48, from a friction coefficient of 0.1/0.15/0.2 and a bearing allowable of 2.4*Fu).

Background:
According to ASME we need 4 bolts to transfer the load, but the engineer says there is no room (always the same excuse) and "we have always used 3 bolts". I told him no deal, so now the project manager wants to know if the American standard is applicable <sigh>.

 

[chicopee]

iceblink,you should start a new thread as you are on a different subject and get rid of this post.

 

[boo1]

Iceblink try:

http://www.leea.co.uk/html/leea-publications/?PHPSESSID=24b0f0b6b91ae3318e67d4e68f8bf131

or attached