Experimental study on the enhancement of additional ribs to the bond performance of FRP bars in concrete

The deficient bond performance of Fiber-reinforced polymer (FRP) bars has impeded their application in concrete structures. To enhance this weak characteristic of FRP bars, the additional ribs as a new anchorage system applied on the bars was proposed in this paper. Its effect on the bond performance of the FRP bars was experimentally investigated through 36 pull-out tests with a centric FRP bar placement in concrete blocks. After the tests, the failure mode and bonding mechanism were discussed. The effects of the types of FRP bar, the anchorage length and the number of additional ribs on the bond properties of bars in concrete were also evaluated. Based on the results, it can be concluded that the additional ribs with radial force contributed greatly to the anchoring force. The utilization of additional ribs also changed the bonding force transferring mechanism between the FRP bars and the concrete. The end bearing that arose from the additional ribs reduced the occurrence of concrete splitting, and thus, the tensile strength of the FRP bars can be fully utilized. The test results also indicated that the additional ribs significantly improved the anchorage performance of the FRP bars in concrete. This improvement would continue with the increase in the number of additional ribs.