A review on the ductility design method of fiber‐reinforced polymer bar and future prospects

Abstract In this paper, the ductility design methods of fiber‐reinforced polymer (FRP) bars were reviewed. It was observed that the graded fracture theory was typically used as the ductility design method of hybrid fiber‐reinforced polymer (HFRP) bar. However, the ductile HFRP bar designed based on the graded fracture theory had the inherent defects of low modulus of elasticity, high yield strain, and post‐yielded sudden drop in stress, which prevented its large‐scale application in civil engineering. In order to eliminate these deficiencies, the authors proposed a novel design concept for a single‐type FRP bar. This novel single‐type FRP bar consisted of highly aligned discontinuous fiber and continuous fiber. The failure mode of this discontinuous/continuous single‐type FRP bar was different from that of the ductile HFRP bar designed based on the graded fracture theory of composite. The tensile ductility of discontinuous/continuous single‐type FRP bar originated from the debonding and stable pull‐out of the discontinuous fiber layer under increasing load. As a result, the post‐yielded sudden drop in stress can be removed for the ductile HFRP bar designed based on the graded fracture theory of composite. In addition, the yield strain can be controlled by adjusting the length of discontinuous fiber layer. In addition, the design configuration, innovative production process, and corresponding theoretical calculations of this novel single‐type FRP bar will be presented in the future. Highlights The ductility design methods of fiber‐reinforced polymer bars were reviewed. Deficiencies of ductile HFRP bar composed of continuous fibers were reported. A novel discontinuous/continuous single‐type FRP bar was foreseen.