The points to be considered in the bending of the ribbed rebars to be used in stirrup construction;

     1. Iron bending mandrel diameters should be used in exactly appropriate sizes calculated according to the diameter of the bent iron as given in the annexes.

     2. Ribbed rebars should never be bent around a sharp object.

     3. Bending operations should be done with the material chosen according to the diameter of the ribbed iron (90, 135, 180 degrees etc.).

You can find the technical information and yield limits required for bending processes in the annexes.