FRP
PRESTRESSING TENDONS: BOND, TRANSFER LENGTH, AND DEVELOPMENT LENGTH
by
Associate Professor of
Engineering Science and
Mechanics
Pennsylvania State
University
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. Thirty beams were pretensioned using a single FRP
tendon. In addition, twelve control beams were pretensioned with a seven-wire
steel strand.
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. Both the
transfer length and development length for FRP tendons were reasonably
predicted by the ACI design equation.