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RE: Torsion in Wide Flange Beam

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Uniform loads do not produce uniform torsional moments just like they do
not produce uniform bending moments.  Only a pure moment, either
torsional or bending, will produce a uniform moment.  You are correct, a
uniform load will produce a torsional moment curve just the same as a
bending moment curve and point loads will produce linearly varying

The parallel between bending and torsional moments hold.  Each goes from
a load to a shear to a moment. (assuming you don't have pure shears and
pure moments.)  While we typically think about torsion as just a moment,
there is an induced torsional shear.

A load inducing a torsion reaches equilibrium similarly to one in
bending.  Remember that when the load starts it is a pure load resisted
by the restraints in the X, Y, Z directions.  The moment is then induced
INTERNALLY within the member, progressively resisted by the member
properties.  Assuming you have a bolted framed beam connection, then the
load on the beam's flange will be externally resisted by a axial forces
in the bolts acting as a couple.  If you weld just the web of the beam
then the resistance is axial forces in each of the welds.

If one connects the flanges of the beam then a fixed (or semi-fixed) end
is created and all of the above changes similarly to how a fixed end
changes bending reactions.


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