Seven T-beams, post-tensioned with straight tendons, were tested to failure to investigate the effect of concrete strength, shear reinforcement, and shear span on the failure mode of externally prestressed beams. Each beam was fabricated with a deviator at the midspan and tested under simply supported conditions. The beams were each subjected to equal concentrated loads at third-points, except for one, which was subjected to a concentrated load at the midspan. Test results indicated that decreasing the concrete strength or the amount of shear reinforcement leads to shear-type failure of the beam. When an appropriate concrete strength and amount of shear reinforcement are provided, flexural-type failure prevails even for shear span to effective depth ratio of as low as 2.5. Analytical considerations based on a strut-and-tie model that was proposed earlier showed good predictions of the ultimate strength and failure mode of the test beams.