Bond behavior and bond strength model for ribbed FRP bar in FRP-confined concrete

In this paper, an experimental study is conducted to gain insight into the bond behavior of ribbed fiber-reinforced polymer (FRP) bar in FRP-confined concrete. Various parameters, including the ratio of concrete cover to bar diameter, concrete strength, and FRP confinement level, are considered in this study. The test results demonstrate the effectiveness of FRP confinement in changing the bond failure mode of FRP bar from the concrete splitting to the pullout and improving bond ductility and strength. The bond response of ribbed FRP bar in FRP-confined concrete is characterized by three distinct stages: uncracked stage, cracking enhancement stage, and cracking degradation stage. The bond mechanism within each stage is elucidated. The study reveals that the normalized bond strength is distinctly influenced by the ratio of concrete cover to diameter and FRP confinement level, while concrete strength exhibits a negligible impact. Finally, the study proposes a novel model for predicting the bond strength of the ribbed FRP bar embedded in both unconfined and FRP-confined concrete. © 2024 Elsevier Ltd