Hello there,
Torsion loads typically promote shear stresses in a structure so assuming that you have no other sources of shear loads, you can investigate shear stresses in your model to see if shear stresses are notable and that may indicate if torsion is present or not.
Regarding the second question (if I understood it correctly), when you are dealing with a quasi-static scenario, the internal loads at the middle of the structure should balance out the external loads considering static equilibrium.
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