ACI 11.6.2.1 states that when Φ_TT_c<T_u torsional reinforcement will be required in accordance with ACI 11.6.3 through 11.6.6.

ACI 11.6.2.2 permits the engineer to design a section for a limiting capacity of Φ_T4T_c as long as the remaining torque is redistributed though the structure. The torsion check will identify one of the three following situations through a design warning when torsion reinforcement is required:

1. Torsion reinforcement required and closed stirrups are assigned to section. The user is responsible for providing the reinforcement. The Beam Design Report provides the maximum factored torsion at all output stations along the beam and also reports Φ_TT_c.
2. Torsion reinforcement required and open stirrups assigned to section. In addition to providing the reinforcement similar to the first warning, the engineer is also reminded that open stirrups, which cannot be used for torsion reinforcement, have been assigned to the beam.
3. The beam cross-sectional dimensions do not satisfy ACI 11.6.3.1. When torsion reinforcement is required the cross-sectional dimensions must satisfy the following:

   $\sqrt{{\left(\frac{V_u}{b_{w}d}\right)}^2+{\left(\frac{T_u{p}_h}{1.7A_{oh}^2}\right)}^2}\le {\varphi }_T(\frac{V_c}{b_{w}d}+8\sqrt{{f^{\prime }}_c})$

   ACI 11.6.3.1 Equation ACI 11-18

   where

   ph,Aoh	=	are calculated in the same way as using the transverse reinforcement bar center line to calculate the section width and depth
   vc,Tu	=	are taken as the maximum values between the critical area defined by ACI 11.6.2.4 and values may not be located at the same location