Experimental Study of Transfer and Development Length of Fiber Reinforced Polymer Prestressing Strands
Z. Lu, T. E. Boothby, C. E. Bakis, and A. Nanni
Appears on pages(s):
bond; development; fiber reinforced polymers; flexure; length; prestressing; strength
An experimental study was conducted to determine the transfer length, development length and flexural behavior of fiber-reinforced polymer (FRP) tendons in prestressed concrete beams. Three kinds of nominally 5/16 in (8 mm) diameter FRP tendons were included in the study: Carbon Leadline, Aramid Technora and Carbon Strawman. Thirty beams were pretensioned using a single FRP tendon. In addition, twelve control beams were pretensioned with a seven-wire steel strand (ST). Transfer length observations from this study were based on concrete strain measurements with a DEMEC gage system. Development length observations were based on three-point flexural tests. Four-point flexure tests were also performed on each material to gain additional understanding of the bond behavior between concrete and the PC reinforcing materials. The "95% average plateau strain" method of using concrete strain results was shown to be an effective way to determine transfer length. By using an appropriate flexural model and extrapolating results from over-reinforced tests to situations where the tendon would actually fail, it was possible to determine development length in this investigation. Despite differences in tendon material properties and prestressing forces, both the measured transfer lengths and the development lengths were almost identical for all tendon materials tested. The development length for FRP tendons was reasonably predicted by the ACI design equation, although transfer length appears to be underestimated.