This Annex gives application rules for the design of members subjected to torsion in building structures. It provides application rules and information for: a) determining the torsion resistance of I, H, channel or structural hollow section members; b) determining torsion constants and warping constants for hot-rolled open sections for use in: - determining torsion resistances; - calculating elastic torsional deformations; - lateral torsional buckling verifications; c) verifying the resistance of members subject to combined torsion and bending or axial force.