Section 22.5 Torsion

Included code sections - 22.5.1, 22.5.3.1, 22.5.3.2, 22.5.4, 22.5.5 (item a and b)

Excluded code sections - 22.5.2, 22.5.3.3, 22.5.5 (item c and d)

Only the core of a cross section is used for torsion design. See Concrete Core Determination .

If the core consists of multiple ribs, then the torsion calculations are performed for an average rib:

rib width = total core width / num ribs
with ultimate forces scaled down by the number of ribs (/ num ribs) and capacity and reinforcement scaled back up by the number of ribs (* num ribs).
code provisions are not applicable to multiple ribs, so to get a more exact calculation, use a separate design section or design strip for each rib.

Equivalent bending moment M_e1 and M_e2 are calculated per sections 22.5.3.1 and 22.5.3.2.

Transverse bending moment M_e3 is calculated and reported in the auditor per 22.5.3.3, but no transverse bending design is performed.

Shear and torsion reinforcement is provided in accordance with sections 22.5.4.1, 22.5.4.2, 22.5.4.3 and 22.5.4.4. In the shear equation for A_v in section 22.5.4.3, " d_t " is substituted for " d_l " to align this equation with the shear equation in 22.4.3.2 when no torsion is present. This change may not be conservative, but is consistent with the publication mentioned in the note below.

Distribution of torsion reinforcement is calculated in accordance with section 22.5.5.

Maximum spacing of torsion stirrups is the least of x₁, (x₁ + y₁)/4 or 200 mm.

If torsion design is selected, at least minimum stirrups will be provided at all locations.

Note: There is a typographical error in the code section 22.5.4.2 for the calculation of V_e1. The term in the numerator should be e_c, not e as shown in the code. Also, equation for T_c in section 22.5.4.1 is typographically incorrect. Refer to publications "Design of Prestressed Concrete Beams Subjected to Combined Bending, Shear, and Torsion" by Rangan and Hall, ACI Journal March 1975 and "Strength of Rectangular Prestressed Concrete Beams in Combined Torsion, Bending, and Shear" by Rangan and Hall, ACI Journal April 1973 for details.