Behavior of Axially Loaded Concrete-Filled Circular Fiber-Reinforced Polymer Tubes

This paper describes the behavior of concrete-filled glass fiber-reinforced polymer (GFRP) tubes under axial compression loading conditions. The study includes completely filled and partially filled tubes with a central hole as well as a tube-in-tube system with concrete filling between the two tubes. The GFRP tubes were designed to provide strength in both the axial and transverse directions and were axially loaded with the concrete core. The study showed that the strength and ductility of concrete are improved due to confinement using GFRP tubes. The highest confinement level was achieved for completely filled tubes. Using a central hole reduces the confinement effect; however, using an inner tube can enhance the confinement for this type of member. Test results indicate that loading of the GFRP tubes reduces the confinement effectiveness. The effects of laminate structure, hole size, interface condition between the tube and the concrete core, stiffness of the tube, and failure modes are discussed.