Abstract
Strength equations based on the skew-bending model have been developed to predict the torsional strength of prestressed concrete beams containing a circular transverse opening and subjected to combined torsion and bending. Test results of 13 axially and eccentrically prestressed concrete beams with web reinforcements are presented. Close agreement is observed between the experimental and the predicted values. The interaction diagrams show that for small T M ratio, mode 1 failure occurs and presence of bending moment reduces torsional strength. For high T M ratio, however, bending moment has no effect on the torsional moment capacity. Compared with the precracking range, the torsional stiffness is very much reduced in the postcracking range. Test results show that eccentric prestressing is more economical than axial prestressing.