Results of thirteen symmetrically prestressed concrete rectangular beams tested under pure torsion are presented. All beams had essentially the same concrete strength, concrete crosssectional area and m, the ratio of the yield force of the longitudinal reinforcement to the yield force of the transverse reinforcement per unit volume, was approximately equal to 2.0. The layout, type, and strength of reinforcement was similar in all beams; the principal variables studied were aspect ratio and amount of reinforcement. The behavior of the beams is compared to the behavior predicted by the space truss with spelling of the concrete cover, the space truss with softening of the concrete, and skew bending. It is shown that the torsional strength of beams with moderate to heavy reinforcement is essentially independent of the aspect ratio. Designers should be aware that this is contrary to the predictions of all three theories and in some cases could lead to unsafe design.
