Influence of Steel Fiber and Rebar Ratio on the Flexural Performance of UHPC T-Beams

To address the bottleneck issues of traditional concrete T-beams, such as excessive self-weight, susceptibility to cracking, and insufficient durability, this study investigates the flexural performance of Ultra-High-Performance Concrete (UHPC) T-beams. Through systematic experiments, the combined effects of three UHPC material ratios and three rebar schemes were analyzed. Six UHPC T-beam specimens were designed, and flexural performance tests were conducted using a staged loading approach, focusing on crack propagation, failure modes, and load-deflection curves to reveal their mechanical behavior and failure mechanisms. The results indicate that steel fibers significantly enhance UHPC toughness. At a fiber content of 1.5%, the specimens exhibited a yield load of 395–418 kN, with an ultimate load increase of 93% compared to the fiber-free specimens. The failure mode transitioned from brittle shear to ductile flexural. Increasing the rebar ratio improved load-bearing capacity, with a 4.58% rebar ratio yielding an ultimate load of 543 kN (51% higher than B1-02), but reduced ductility by 36%. Steel fibers restricted crack widths to 0.1 mm via crack-bridging effects, raising the cracking load by 53% and the shear capacity by 2.8 times. UHPC mix ratio adjustments had a limited impact on beam performance at the same fiber content. Overall, UHPC T-beams exhibited a compressive concrete crushing-dominated failure mode, with load-deflection curves showing a 42% gentler slope than conventional concrete. The ductility coefficient ranged from 3.8 to 5.2. For engineering applications, it is recommended to maintain a steel fiber content of at least 1.5% and a rebar ratio of 2.5–4.0% to strike a balance between strength and ductility.