Column Torsion Check

The torsion check is provided to identify columns that require torsion reinforcement.

Torsional reinforcement is not required when:

T_{u} < ϕ \sqrt{{f^{'}}_{c}} (\frac{A_{c p}^{2}}{p_{c p}}) = ϕ_{T} T_{c}

ACI 11.6.1

where

A_cp	=	hb
p_cp	=	2(h + b)

In addition, if the beam/column has axial load an additional check is performed:

T_{u} < ϕ T_{n}

ACI 11.6.1(c)

T_{n} = \sqrt{{f^{'}}_{c}} (\frac{A_{c p}^{2}}{p_{c p}}) \sqrt{1 + \frac{N_{u}}{4 A_{g} \sqrt{{f^{'}}_{c}}}}

\frac{N_{u}}{4 A_{g} \sqrt{{f^{'}}_{c}}} < - 1

ACI 11.6.2.1 states that whenϕ_TT_c ≥ T_u torsional reinforcement is required in accordance with ACI 11.6.3 through 11.6.6. The torsion check will generate a design warning when torsion reinforcement is required.

Note: ACI 11.6.3.1 is not checked for columns to see if the column cross-sectional dimensions will permit torsional reinforcement.