To investigate the bending response of ultra-high-performance concrete (UHPC) beams reinforced with hybrid glass-fiber-reinforced polymer (GFRP) and steel bars, five specimens were tested in four-point bending in the present experimental study. The effect of varying reinforcement ratios on the flexural behavior was evaluated. It was observed that all tested beams failed due to reinforcement yielding while maintaining satisfactory ductility; the failure mode was characterized by yielding of the bottom tensile reinforcement followed by crushing of the UHPC in the compression zone. When the steel reinforcement ratio increased from 2.03% to 2.42% and 3.08%, the beam load-carrying capacity increased by 6.27% and 14.34%, respectively. When the GFRP reinforcement ratio increased from 0.91% to 1.19% and 1.51%, the peak load-carrying capacity increased by 9.58% and 15.55%, respectively. Based on reasonable assumptions, analytical formulas were proposed to predict the cracking moment and the flexural capacity of the UHPC beams reinforced with hybrid GFRP and steel bars, with errors within ±5%. By fully accounting for the bridging effect of steel fibers, modified coefficients were introduced to estimate beam deformation and crack width, along with corresponding calculation methods. The proposed formulas accurately predicted cracking moment, ultimate moment, deflection and crack width for the beam. The findings propose a theoretical basis for the design and application of UHPC beams reinforced with hybrid GFRP and steel bars.
Shi et al. (Wed,) studied this question.