Generalized Softened Variable Angle Truss Model for PC Beams under Torsion

In a previous study, a new model (Generalized Softened Variable Angle Truss Model—GSVATM) was proposed to compute the global behavior of reinforced concrete beams under torsion, including for low loading stages. In this article, the GSVATM is extended to cover prestressed concrete (PC) beams under torsion, with longitudinal and uniform prestress. The changes in the GSVATM, in order to include the influence of the initial stress state due to prestress, the contribution of the prestress reinforcement after the decompression of concrete and the constitutive laws for prestress reinforcement, are presented, as well as the solution procedure. The theoretical predictions of the extended GSVATM are compared with experimental results of PC beams under torsion, where good agreement is observed in terms of stiffness, transition from the non-cracked stage to the cracked stage and also in terms of the maximum torque. It is also shown that when compared with the predictions of some codes of practice, namely for the cracking and ultimate torque, the estimates from the GSVATM are in general more accurate.