Bond Strength Prediction Model of Ribbed FRP Bars in Concrete

The bond behavior of Fiber-Reinforced Polymer (FRP) bars is a critical factor in the mechanical performance of FRP rebar reinforced concrete structures, but until now, there has been limited research on the effect of rib forming process and geometrical features of ribbed FRP bars on the bond behavior, and no relevant provisions are incorporated into the current main design codes. In the paper, the spirally-glued FRP bar was taken into consideration, and bond test data were collected to investigate the main test parameters on the bond failure modes and bond strength. Greater emphasis was placed on the effect of rib forming process and geometrical features of such ribbed FRP bars on bond behavior. Results shown the macroscopic failure mode was pullout failure. More specifically, the spirally-glued FRP bar mainly exhibited shearing off of FRP bar ribs, and bond strength increased by increasing concrete strength. Spirally-glued FRP bars shown higher bond strength by increasing concrete cover which contributes to better confinement to FRP bars. Bond strength of spirally-glued FRP bars could be improved by increasing relative rib height hrd and FRP bar rib width ratio Fr. Multivariate nonlinear regression was adopted to propose a suitable formula to estimate bond strength. The calculated results by the proposed equation were in good agreement with the test results with greater accuracy than the current design codes. This is because the effect of rib forming process and geometrical features of FRP ribs on bond strength is accurately accounted in the proposed equation.