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## How is this torsion?

 Essentially we got combined forces here. My problem is that I could use your same logic in this pic To say that there's no bending, only torsion.
In the picture I drew, there is a combination of bending and torsion.
All layers are bent into the direction of the force.
But there is also torsion between the top and middle layer, and reverse torsion between the middle and the bottom layer.

 The pin is pretty far from the wall!
So?
Is there a force component along the length of the profile?
Anyway, as PhanthomJay remarked, you have vertical shear in both the beam and weld.

When you were originally doing mechanics, you learned that you had horizontal forces that had to balance out, vertical forces that had to balance out, and a moment that had to balance out.
These were external forces that were applied to each component.
Now you also have bending, shearing, and torsion within each component to take into account.
That's what you get from leveling up. ;)

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That is really big, indeed. Sorry for my response also being of the same order of magnitude in size. I want to point out that in your formula $ρ_s = F/\Sigma l$, that is the formula for the vertical shear in the weld in units of force per length of weld. It should not be confused with the shear stress in the beam. As has been pointed out, both the beam and welds are subject to bending and shear stresses from forces and and moments. Both the beam and weld must be designed accordingly, so don't confuse the 2.