Flexural behavior of ultra-high-performance fiber-reinforced concrete beams reinforced with GFRP and steel rebars

• The use of UHPFRC has benefits on improving ductility and deformability.
• Higher reinforcement ratio of GFRP bar provides better flexural performance.
• Ductility and deformability are insignificantly affected by hybrid reinforcing system.
• Flexural response of UHPFRC beam is successfully predicted by sectional analysis.

This study describes the flexural behavior of ultra-high-performance fiber-reinforced concrete (UHPFRC) beams reinforced with glass fiber-reinforced polymer (GFRP) rebars and hybrid reinforcements (steel + GFRP rebars). Three GFRP bar-reinforced beams and four hybrid reinforced beams with different reinforcement ratios were fabricated and tested. Owing to the strain-hardening characteristics of UHPFRC, all test beams exhibited very stiff load–deflection behavior after the formation of cracks and satisfied the service crack width criteria of CAN/CSA S806. In addition, deformability factors higher than the lower limit of CAN/CSA-S6 were obtained for all test beams. The increase in the reinforcement ratio of GFRP rebars resulted in the improvement of their flexural performances, including post-cracking stiffness, load carrying capacity, and ductility (or deformability). The use of hybrid reinforcements by replacing a part of a GFRP rebar with a steel rebar contributed to a higher post-cracking stiffness before steel yielding, but led to lower deformability. Based on a sectional analysis, both AFGC/SETRA and JSCE recommendations were appropriate for predicting the moment–curvature response of UHPFRC beams with GFRP rebars and hybrid reinforcements: the average ratios of the maximum moments obtained from experiments and numerical analyses were found to be 1.12 and 0.94, respectively.