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How is this torsion?

by Femme_physics
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PhanthomJay
#19
Dec3-12, 02:43 PM
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Quote Quote by Femme_physics View Post
There is shearing according to the solution.

1st) Shearing 2nd) Torsion



Sorry for the img being so big.

Essentially we got combined forces here.
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 [itex] ρ_s = F/\Sigma l[/itex], 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.
pongo38
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Dec5-12, 12:16 PM
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That's an awful lot of correspondence and really it's just the use of terms and a point of view. The weld group is subjected to a tension, a shear and a moment about the centroid of the weld group, about the axis perpendicular to the paper. If someone wants to call that moment a torsion, why shouldn't they? It's not a bad use of the term in this case, because it causes shear stresses in the welds, and shear stress is usually associated with torsion in a solid member. What it does not represent is a torsion on the beam itself. That is bending. But we are discussing the weld group...
Femme_physics
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Dec7-12, 01:11 AM
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In the picture I drew, there is a combination of bending and torsion.
Yes, however in the original exercise we didn't take bending into account, how come?
PhanthomJay
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Dec7-12, 05:28 AM
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Going back to your original problem in post 1, there is some confusion as to
1.) whether you are looking at loads and streses on the on the weld group or the beam,
2.) whether the beam is an I beam, an open channel 'U' -tube, a semi-circular open tube, etc.,, and
3) whether the load at the end is applied at the center of the cross-section or eccentrically applied at the right side of the cross section.

looking at the beam and assuming it is an I beam withthe load applied at the center of the cross-section, there is bending and vertical shear and axial loading in the beam, no torsion;
looking at the weld for this load case, it is subject to vertical shear, horizontal shear, and torsion.

This appears to be the most likely scenario.

If the load was applied off center along the edge of the cross section, there is still bending, vertical shear, and axial load in the beam, as well as torsional shear stresses in the beam from the eccentrically applied load that causes a twisting moment. Important thing here is that there is still bending....must be. For the weld group for this case, we have vertical shear, horizontal shear, and torsion in 2 directions.


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