In this study, 18 development length tests were carried out on single strand rectangular and multiple strand T-shaped semi-lightweight beams having design compressive strengths of 7000 psi (48 MPa). In the rectangular beam tests, the design moment capacity was exceeded in all specimens. However, in the T-beam tests, bond failures at loads below the design capacity occurred in some specimens immediately after the formation of a flexure-shear crack near the loading point. Additional T-beam tests showed that the bond failure associated with flexure-shear cracking could be prevented by increasing the transverse reinforcement near the point of maximum moment. The shift in the tension force that occurs when flexural cracks turn diagonally needs to be considered when determining if sufficient anchorage of strands is provided. Therefore, the authors recommend that the current AASHTO and AC! requirements for strand development should be enforced at a “critical section�? that is located a distance cJ from the point of maximum moment towards the free end of the strand, where d is the distance from the extreme compression fiber to the centroid of the prestressed reinforcement.
