The concept of the space truss analogy is based on the assumption that the torsional capacity of a reinforced concrete rectangular section is derived from the reinforcement and the concrete surrounding the steel only. In this case, a thin-walled section is assumed to act as a space truss. The inclined spiral concrete strips between cracks resist the compressive forces, whereas the longitudinal bars at the corners and stirrups resist the tensile forces produced by the torsional moment.
