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Torsional design is made with the reinforcement requirement determined by comparing the factored torsional moment T_u value with the threshold torsion T_th and cracking torsion T_cr values.

• Torsional effects can be neglected if the factored torsional moment at section T_u is less than threshold torsion multiplied by strenght reduction factor ϕT_th (T_u<ϕT_th). Torsional moments that do not exceed the threshold torsion T_th will not cause a structurally significant reduction in either flexural or shear strength and can be ignored.

• If T_u ≥ ϕT_cr it is assumed that the torsional resistance is provided by closed stirrups, longitudinal bars, and compression diagonals. Therefore, the reinforced concrete member is designed to resist T_u.

• If ϕT_cr > T_u ≥ ϕT_th, only minimum tension rebar needs to be provided ACI 9.6.4.

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minimum area of longitudinal reinforcement A_l,min

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