Novel Narrow Closed FRP Stirrups Fabricated by a Filament Winding Process: Concept and Behavior

Fiber-reinforced polymer (FRP) stirrups present an effective solution to the perennial corrosion issue of steel stirrups. However, existing products of FRP stirrups suffer from various issues including significant strength reduction in the corner regions, and they may pose negative effects on the flexural stiffness/strength of shallow RC members due to the relatively low transverse stiffness of FRP. To address these issues, this paper presents the concept of a novel form of narrow closed FRP stirrups fabricated by a filament winding process as well as a study to demonstrate their fabrication process and mechanical behavior. The study has shown that the novel stirrups including the proposed surface profiles (ribbed and sand-coated surfaces) can be readily manufactured using a filament winding machine. It has also been shown that the novel stirrups are superior to most pultruded FRP stirrups in terms of bent strength, and they can effectively improve the shear capacity of RC beams. Furthermore, the proposed surface treatment methods (i.e., rib-forming and sand-coating) were shown to significantly improve the force-transfer mechanism between the novel stirrups and concrete.