Shear Strength of Post-Tensioned Daps in Prestressed Concrete Beams

In prestressed concrete beams with dapped ends, inclined shear cracks appear frequently at early stages of loading. A theoretical solution based on elasticity methods was formulated to represent the onset of failure at the dapped regions. The solution gave a quantitative prediction of the critical tensile stresses at a point close to and very near the dap root. Experiments were conducted on six prototype prestressed concrete T-beams. The beams were pretensioned longitudinally and were provided with post-tensioned, high-strength, steel web reinforcement. The variables included: (1) geometry of the dapped ends; (2) type of web reinforcement in dapped regions; (3) ratio of shear span to depth of beam; and (4) prestress level. The results indicated that shear strength of prestressed concrete beams can be predicted with reasonable accuracy, and that dapped regions can be prestressed with inclined high-strength steel bars to control shear cracking at the working load.