So say I have a steel pipe under a torque and an axial load. I want to know whether the axial load has any effect on the twist due to torque. Have one calculation which (perhaps falsely) assumes the pipe is made of lots of axially running "wires" and calculates the torque due to this axial force on slightly twisted "wires". See the attachment. However the simple Ansys model I've done shows absolutely no effect on torsional stiffness when an axial load is applied. Thoughts?