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Double weld on pole

Double weld on pole

Double weld on pole

(OP)
Guys,

I need some help with basic statics here. Please see the image attached. While calculating bending force due to loading how can I take advantage of the Style B over Style A.

Since there are 2 welds holding in the style B, it should better design compared to style A. But, how can I alter the formula for taking this advantage?

Thanks,
GC

RE: Double weld on pole

Generally speaking in "Style A" the welds are experiencing tension (caused by bending) and shear. the tension force is large because the moment arm causing tension/compression is small (basically the upper pipe dia.). In "Style B" the welds are in shear only. The bending is now taken as shear on the weld group with the tension/compression moment arm taken as the distance between welds. The moment arm has increased significantly and this would decrease the force on each weld group.

I have provide a simple explanation. You should also consider weld fatigue if you have cycled loading along with components of gravity loading and torsion.

RE: Double weld on pole

What do you mean by "bending force?" Force on what?

It won't help the pole any so long as your weld is OK.

You could regard in style B that the base of the pol is fixed and the weld part way up adds some stiffness to the pole but you need to analyse it for the loads and forces where they are.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Double weld on pole

In both cases, the bending moment at the joint between the smaller dia. pole and the larger dia. base is the same. This means the upper pole requires the same section size regardless of which option is used.

As CBEngi notes, the weld stress in the first option will be higher, as the bending moment decouples into tension / compression over a circular weld with a small circumference. In the second option, the bending moment decouples into shear over both the top and bottom welds (equal and opposite). As this occurs over a longer distance (from top weld to bottom weld) the weld stresses will be less than the first option.

In other words, there is no difference in the requirements for the smaller dia. pole between either option, but the weld stresses will be less in the second option.

That said, it might well be more efficient to just use a larger weld on the first option, rather than adding an additional ring stiffener and weld as per the second option...

I presume the top ring in the first option is sufficiently stiff to resist the push / pull forces in the weld...

RE: Double weld on pole

I'm not sure option B could even be constructed reasonably.

RE: Double weld on pole

Agree - but the lower weld could be done from the bottom (as is indicated) prior to the bottom of the pipe assembly being closed in. Not sure what that larger base rectangle represents.

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