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[FAQ]

Nodal coordinates do not change in small deflection problems. Moreover, small deflection theory assumes that the deflections are so small that the final shape is the same as the original geometry, so no updating of the stiffness matrix based on deformation occurs. Thus, while a node is expected to move in a circumferential fashion under an applied torque, the nodal coordinate system is Cartesian, so it gives the impression that the node is moving tangent to its original shape, thus increasing the radius. A further cause of confusion is that, for small deflection problems, results are scaled (exaggerated), which makes the radius seem as if it is changing.
If the calculated or imposed rotation is expected to be large, using large deflection theory (with a large enough number of substeps) will be more appropriate and give expected result plots.