The use of high-strength reinforcing steel is an effective way to improve the flexural efficiency of reinforced concrete beams. However, the flexural behaviour of beams reinforced with 630 MPa grade longitudinal rebars in combination with normal-strength concrete is still not fully understood, especially with regard to serviceability performance. In this study, the flexural performance of simply supported RC beams reinforced with HRB500, HRB600 and HRB630 longitudinal rebars and cast with C60 steel-fibre-reinforced concrete was investigated through a combined experimental and numerical approach. Six beams were tested under four-point bending to examine cracking patterns, deflection development and ultimate flexural capacity. A three-dimensional nonlinear finite element model based on the Concrete Damage Plasticity model in ABAQUS was then established and calibrated against the test data. Using the validated numerical model, a parametric study was carried out to investigate the influence of steel grade, tensile reinforcement ratio on flexural stiffness and ductility. Test results indicate that, for the same reinforcement ratio, the ultimate moment capacity of HRB630 beams is about 8% higher than that of HRB600 beams and about 25% higher than that of HRB500 beams, while a ductile flexural failure mode governed by yielding of tension reinforcement is still maintained. The study also shows that for HRB630 beams, deflection predictions need to account for the higher steel stress level and the deterioration of tension stiffening effects. In general, the results demonstrate that HRB630 high-strength rebars can be safely and efficiently used in flexural members when the tensile reinforcement ratio is kept within the under-reinforced range and steel-fibre-reinforced concrete is adopted to improve cracking and deflection performance.
Li et al. (Mon,) studied this question.