Torsion forms one of the four major structural action besides axial force, shear and bending

Members in a structure are rarely subjected to pure torsion.

Normally, torsion is accompanied by shear and flexure, and it has only a secondary effect.

Torsion may occur either due to eccentric loading not lying in the bending plane, or due to transfer of rotation between interconnected members.

Based on its type of action, torsion is classified into two categories.

a. Compatibility torsion

b. Equilibrium torsion