Behavior of FRP spiral-confined concrete under concentric compression

Fiber-reinforced polymer (FRP) composites are emerging as potential construction materials for concrete members, particularly for marine structures where durability is of critical importance. While a comprehensive analysis has been executed on FRP-reinforced concrete columns, limited investigation has been undertaken to explore the confinement mechanism of pure FRP spiral-confined concrete (FSCC) without longitudinal FRP bars. For an efficient and reliable assessment of FRP reinforced concrete columns, it is critical to precisely predict the axial stress-strain relationship of FSCC. Therefore, an experimental investigation was performed to examine the compressive behavior of FSCC. The critical test variables included the pitch of FRP spiral, material type of spiral, and reinforcement diameter of FRP spiral. The test results demonstrated that the confinement of FRP spiral could substantially increase the ultimate axial strain and compressive strength of concrete, enabling a ductile failure manner of FSCC specimens. The axial stress-strain response of FSCC exhibited an approximately bilinear behavior, with the compressive stiffness of the second linear portion being influenced by the material properties and volumetric ratio of FRP spiral. Additionally, the effectiveness of a most newly-developed axial stress-strain model for FSCC was assessed utilizing the test results of this study.