Study on the Flexural Performance of High-Strength Concrete Beams Reinforced with Hybrid GFRP Bars and High-Strength Steel Bars

To investigate the flexural behavior of high-strength concrete beams reinforced with a hybrid configuration of GFRP bars and high-strength steel bars, four-point bending tests were conducted on five C80 high-strength concrete beams, with the reinforcement ratios of high-strength steel bars and GFRP bars taken as the main variables. Combined with finite element simulation and theoretical analysis, the failure modes, load–deflection responses, crack development, and reinforcement strain characteristics of the test beams were examined. The results show that all test beams exhibited flexural failure with an appropriate reinforcement ratio, characterized by yielding of the high-strength steel bars in the tensile zone and crushing of the concrete in the compression zone. Increasing the GFRP reinforcement ratio primarily enhanced the peak load and post-cracking stiffness, whereas increasing the HRB635 reinforcement ratio had a more pronounced influence on the yield load and sectional stiffness. The strain distribution at the midspan section generally conformed to the plane-section assumption, and the two types of reinforcement demonstrated good collaborative load-bearing behavior and deformation compatibility. The established finite element model accurately simulated the load–deflection responses, crack evolution, and failure patterns of the test beams. A distinct post-yield load-carrying stage was observed: after yielding of the HRB635 steel reinforcement, the GFRP bars remained in the linear–elastic range and continued to carry increasing tensile force until crushing of the C80 concrete in compression. Based on this experimentally identified failure sequence, a normal-section flexural capacity model was developed in which the HRB635 reinforcement is taken as yielded while the GFRP stress is determined from sectional strain compatibility rather than directly assigned its tensile design strength. The predicted capacities agreed well with both the experimental and finite element results.