Abstract
Test results of 17 axially prestressed concrete beams without stirrups and containing a transverse circular opening are presented. Mainly, beams having two different opening diameters were subjected to various combinations of torsion and bending. Test results show that the bending moment has a beneficial effect and increases the torsional strength for beams with high T/M ratios. For beams with low T/M ratios; however, the torsional strength decreases rapidly with increasing the bending moment. Strength equations to predict the torsional strength at initial cracking are developed. Based upon the initial cracking strength, empirical equations are suggested to predict the ultimate torsional strength for all combinations of torsion and bending. The proposed equations predicted closely the torsional strength of the test beams. Comparison of similar prestressed concrete beams with and without stirrups shows that the introduction of stirrups promotes the development of a consistent failure pattern and increases the ductility and the torsional strength considerably.