Equilibrium Torsion

Equilibrium Torsion occurs when the torsional moment is required to be in equilibrium and maximum torsional moment (T_u) cannot be reduced by redistribution of moments. In this case the torsion reinforcement must be provided to resist all of T_u. This type of torsion is also known as primary torsion. In Etabs or other programs we can not release torsion in this case.

Example: An edge beam supporting cantilever slab.

Compatibility Torsion

Compatibility Torsion occurs when the torsional moment can be reduced by the redistribution of internal forces while compatibility of deformation is maintained in the member. This type of torsion is also known as secondary torsion. In Etabs or other programs we can release torsion in this case.

Example: An edge beam supporting two transverse beams producing twisting moment.