I wanted to see if the force acting at A (30 kN) would create a deflection from OB other than twist. In other words, would a force perpendicular to the axis of rotation cause anything other than twisting?

  • $\begingroup$ What have you tried to convince yourself one way or another? Showing what math or thinking you have done so far will help people answer. For example, try free body diagrams - what are the reactions at point O, or, cutting the part to look at equilibrium of bar AB, what are the forces at B that are applied to to tube OB? What do these FBDs tell you about the loads tube OB is subjected to? $\endgroup$ – CableStay Jul 22 '20 at 14:37
  • $\begingroup$ “Yes”. Try it with two rulers taped together and see what happens. $\endgroup$ – Jonathan R Swift Jul 22 '20 at 14:39

This is a riff on @kamran's answer, but I hope it's different enough to be worthwhile.

Look at the arm AB, and the action of the upward force. Now do the statics around just the arm -- you'll find that at point B, there is an upward force and a moment.

As long as the deflection in the member from B to O is small enough, and nothing hits its elastic limit or just plane breaks, you can separately calculate the effect of the torque from the effect of the upward force. When you're done, you can add those effects together for a final answer.


Yes the force will have at B a torque of

T= -30* 0.8= -24kN.m

And BO will act as a cantilever beam under 30kN upward load. The moment upward at 0 will be:

M= 30kN * 1.2 =36kN.m upward.

Assuming up as positive sign fo force.

So the BO will both twist clockwise and bend upwards. Below is an exaggerated sketch of the deflected bar.

deflected rod

  • $\begingroup$ Thanks Karmran, to clarify are you saying that 30KN can be placed at point B ? Also if rod OB was connected to handle AB through two keys, would that change anything? $\endgroup$ – Nick Jul 22 '20 at 21:25
  • $\begingroup$ Yes you could replace the original load with a 24kN torque and a 36kN vertical load at B. And unless we wand to analysis the stresses at be the details of the handle AB connection at B are not relevant as long as they are strong enough to apply the torque and P load at B. Like you could weld it or use 4 screws or tie it tight with a rope. $\endgroup$ – kamran Jul 22 '20 at 21:51

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