This paper presents test results of an experimental investigation carried out on 12.68-in.-diameter (322 mm) and 13.8-ft-long (4.2 m) prestressed concrete–filled fiber-reinforced polymer tubes (PCFFTs). A total of five PCFFT specimens and one control specimen, manufactured with steel spiral reinforcement instead of the fiber-reinforced polymer (FRP) tube, were tested in four-point bending. Four PCFFTs were pretensioned and one was post-tensioned using unbonded strands. Prestressing strands were oriented in a circular pattern symmetric about the tube’s longitudinal axis. Other parameters investigated were prestress level, laminate structures of the FRP tubes, and number of strands. One PCFFT was also compared with a concrete-filled FRP tube without any steel reinforcement. Test results indicate that prestressing not only improves the strength and serviceability of the system substantially but it also activates a confinement mechanism of the concrete core restrained by the FRP tube. In these specimens, the FRP tubes confine more concrete than the steel spirals and also contribute longitudinally as reinforcement, leading to significant enhancement of the members�? flexural strengths.
