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Torsion of a beam

Torsion of a beam

Torsion of a beam

(OP)
Hello all, I have a question of the analysis of a steel wide-flange beam.

It's a beam with essentially 5 equally spaced point loads acting on the top flange at an angle (roughly 68.5 degrees from horizontal) which I assumed generates some torsion. The beam is double coped on either end, and the web is welded to end plates which are embedded into masonry/concrete walls. At each point load, there are 3/8" transverse stiffeners on each side of the beam, full height.

This beam already exists and our company was consulted about the adequacy of adding a cantilever flagpole to the web of the steel beam on one end. I'm currently looking at the combination of shear and torsion at the cross section of where the beam is double-coped. (So it's 15" x the web thickness, 0.3")

My question is this: Is the half the total torsion seen by the beam from the five point loads carried on either end of the beam? We're assuming it's simply supported. My colleague thinks the torsion is internally resisted, similar to a bending moment, and the connection at either end doesn't see torsion from the point loads.

Thanks for your input!

RE: Torsion of a beam

draw a free body ... 1/2 torsion reacted at both ends is probably reasonable

another day in paradise, or is paradise one day closer ?

RE: Torsion of a beam

Quote (AnimusVox)

Is the half the total torsion seen by the beam from the five point loads carried on either end of the beam?

Yes, absolutely.

Quote (AnimusVox)

My colleague thinks the torsion is internally resisted, similar to a bending moment, and the connection at either end doesn't see torsion from the point loads.

Have your colleague draw the free body diagram. He's out to lunch in a pretty fundamental way. A simple span flexural beam doesn't require flexural restraint at the supports for equilibrium. A simple span torsional beam does require torsional restraint at the supports for equilibrium.

Transferring torsion through just the double coped web is a terrible, flexible detail prone to a lot of uncertainty. Hopefully your loads are small.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Torsion of a beam

a typical beam in bending has all the loads in the same plane.

if your reactions are in the same plane as the loads, then there'll be no torsion; but I'm willing to bet that this plane won't align with the centroid of the support (and so there'll be a torsion).

another day in paradise, or is paradise one day closer ?

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