Prestressed Concrete Beams with Small Opening Under Torsion

Abstract

Based on the familiar skew‐bending model, strength equations are developed to predict the torsional strength of prestressed concrete beams containing a small circular transverse opening and subjected to torsion. Test results of fourteen axially and eccentrically prestressed concrete beams with and without web reinforcements are presented. Close agreement is observed between the experimental and the predicted values. Introduction of web reinforcement in prestressed beams changes its brittle failure characteristic to a ductile one and improves torsional strength. Torsional strength and stiffness of prestressed beams, however, decrease with the increase of opening size. Tension crack inclinations in prestressed members under torsion are considerably less than 45°; spacing of stirrups is, therefore, larger than that for non‐prestressed members. Comparison of test results of axially and eccentrically prestressed beams shows that eccentric prestressing is more economical than axial prestressing.