Behavior of GFRP bar-reinforced hollow-core polypropylene fiber and glass fiber concrete columns under axial compression

This study experimentally investigated the behavior of glass fiber-reinforced polymer (GFRP) reinforced hollow-core concrete specimens under concentric axial compression. The effect of the type of concrete (non-fibrous concrete, i.e., normal concrete without the addition of fibers; polypropylene fiber concrete; and glass fiber concrete) and pitches of the GFRP helices on the behavior of GFRP bar-reinforced hollow-core concrete specimens were investigated. The experimental program consisted of seven circular hollow-core specimens with an outer diameter of 214 mm, an inner circular hole diameter of 56 mm, and a height of 850 mm. The failure modes, axial load carrying capacity, and ductility of GFRP bar-reinforced hollow-core concrete specimens were investigated. The experimental results showed that, for a similar amount of reinforcement, the GFRP bar-reinforced hollow-core polypropylene fiber concrete (GFRP–HC–PFC) specimen achieved 2% higher maximum axial load and 19% higher ductility than the GFRP bar-reinforced hollow-core non-fibrous concrete (GFRP–HC–NFC) specimen. For a similar amount of reinforcement, the GFRP bar-reinforced hollow-core glass fiber concrete (GFRP–HC–GFC) specimen achieved 14% lower maximum axial load but 9% higher ductility than the GFRP–HC–NFC specimen. The axial load carrying capacity and ductility of the specimens enhanced with the close pitch of the GFRP helices. A simplified equation was developed for GFRP bar-reinforced hollow-core concrete columns, which predicted the axial load capacity of the specimens with reasonable accuracy.