ABSTRACT
This chapter applies the softened truss model to members subjected to torsion. It presents the governing equations for equilibrium condition and compatibility condition, and presents the softened constitutive equations for concrete struts in bending and compression. The chapter lists the 18 governing equations for a torsional member in 3 categories: the 4 equilibrium equations, the 7 compatibility equations, and the 7 constitutive equations. In a torsional member, the angle of twist θ also produces warping in the wall of the member, which, in turn, causes bending in the concrete struts. The maximum torsional resistance can be used to check the minimum size of cross section in the design of torsional beams. Three limitations are required in practical design: minimum torsional reinforcement, limitation of the angle α to prevent premature failure, and limitation of the angle α to prevent excessive cracking.
