Performance of bent stirrup and headed glass fibre reinforced polymer bars in concrete structures

An experimental investigation was conducted to evaluate the performance of various types of glass fibre reinforced polymer (GFRP) reinforcement, including bent stirrups and headed bars in concrete structures. Results from 11 large beams (400 mm × 650 mm × 3650 mm) tested in monotonic three-point flexure were selected for this paper; some specimens used GFRP bent-bar stirrups and some used double-headed straight bar shear reinforcement. Based on the results from the tests, specimens reinforced with bent-bar stirrups and specimens with headed-bar shear reinforcement were found to perform similarly up until the calculated flexural failure load. Beyond that, beams reinforced with bent-bar stirrups showed significantly more deformability due to confinement of concrete in flexural compression. Strains measured in the transverse reinforcement were found to exceed the code limitations, in some cases exceeding 200% of the limit prescribed in both CSA S6 and ACI440.1R. It was also found that at loads close to the service conditions, the cracking behaviour was very similar for the beams reinforced with transverse headed bars and bent-bar stirrups. Finally, the concept of hybrid reinforcement systems for controlling deflections and cracking was introduced. Results from the experiments show promise that these systems can better control deflections and cracking at expected service load conditions.