Chapter 40Limit State of Collapse: Torsion

40.1 General

In structures, where torsion is required to maintain equilibrium, members shall be designed for torsion in accordance with 40.2 to 40.4. However, for such indeterminate structures where torsion can be eliminated by releasing redundant restraints, no specific design for torsion is necessary, provided torsional stiffness is neglected in the calculation of internal forces. Adequate control of any torsional cracking is provided by the shear reinforcement as per 39.

NOTE — The approach to design in this clause is as follows: Torsional reinforcement is not calculated separately from that required for bending and shear. Instead the total longitudinal reinforcement is determined for a fictitious bending moment which is a function of actual bending moment and torsion; similarly web reinforcement is determined for a fictitious shear which is a function of actual shear and torsion.

40.1.1 The design rules laid down in 40.3 and 40.4 shall apply to beams of solid rectangular cross-section. However, these clauses may also be applied to flanged beams, by substituting $b_{w}$ for b in which case they are generally conservative; therefore specialist literature may be referred to.

40.2 Critical Section

Sections located less than a distance $d$, from the face of the support may be designed for the same torsion as computed at a distance $d$, where $d$ is the effective depth.

40.3 Shear and Torsion

40.4 Reinforcement in Members Subjected to Torsion

40.4.1 Reinforcement for torsion, when required, shall consist of longitudinal and transverse reinforcement.