Transfer and development lengths of FRP prestressing tendons

An experimental investigation was conducted to determine the transfer length, development length, and flexural behavior of fiber-reinforced polymer (FRP) tendons in prestressed concrete beams. Three types of nominally 5/16 in. (8 mm) diameter FRP tendons were included in the study: Carbon Leadline, Aramid Technora, and a carbon fiber reference material. Thirty beams were pretensioned using a single FRP tendon. In addition, twelve control beams were pretensioned with a seven-wire steel strand (ST). The transfer length for FRP tendons was reasonably well predicted by the ACI design equation, with the modification in AASHTO providing for a minimum transfer length. The ACI equation predicts the development length very conservatively provided the tendon rupture stress is used in place of the tendon stress at nominal capacity. Therefore, it is proposed to modify the ACI equation to account for the larger bond stress developed by the FRP tendons.