Effect of Helical Wrapping on Fatigue Resistance of GFRP

Abstract

Winding helical fiber around fiber reinforced plastic (FRP) rods, which serve as concrete reinforcement, is used to enhance the bond between the rod and the concrete. A theoretical analysis of the strain development in the helical fiber when the rod is subjected to tension shows that the fiber may shorten or lengthen, depending on the winding step size of the helical fiber and the Poisson coefficient of the rod. When the rod is subjected to cyclic loading, extensive damage is caused to the longitudinal fibers by lateral load imposed by the helical fiber, which may lead to a premature failure of the rod. An experimental study on the fatigue behavior of helically-wrapped glass fiber reinforced plastics (GFRP) rods showed that the longitudinal fibers in the region underneath the helical fiber fractured locally by local shear or bending, while the other fibers in the core broke under direct tension. A microscopic study of the fibers along the rod after cyclic loading showed extensive damage to the fibers located under the helical fiber.