Evaluation of bond strength of helically ribbed CFRP bar connections as mechanical anchorage schemes

In spite of their outstanding properties, FRP reinforcing bars still face a series of drawbacks that should be addressed to widen their applications. For example, straight FRP bars must be used because those bars suffer significant strength degradation when curved. This implies that FRP bars resist the slip nearly solely through their bond strength with concrete. In addition, helically ribbed FRP bars exhibit bond strength twice higher than sand coated bars but develop weaker bond characteristics with concrete than the steel rebar. Anchorages are thus needed to improve the bond strength but may be difficult to realize in narrow spaces like joints. Therefore, this study examines the combined use of helically ribbed FRP bars with connections like lap-splice, epoxyfilled tube, coupler or expanded ribs as mechanical anchorages. A total of 36 pullout specimens considering the types of connection as parameter are tested to investigate the eventual effectiveness of the connections in enhancing the bond behavior. The use of two expanded ribs appears to be the best option. The predictions of the bond stress-slip models of current design codes are compared to the experimental data to examine whether these models can simulate accurately the connections.