Experimental and Empirical Study on the Shear Behavior of Steel Fiber–Reinforced Concrete Beams with High Fly Ash Content

This study presents an experimental investigation into the shear strength of reinforced concrete (RC) beams devoid of shear reinforcement, incorporating crimped steel fibers and high-content fly ash as a partial replacement for fine aggregate. Twelve concrete mixtures were designed with fly ash replacement levels of 25%, 50%, and 75%, combined with steel fiber volumetric contents of 1% and 1.5%. Shear performance was evaluated through four-point bending tests on simply supported beams featuring varying shear span-to-depth (a/d) ratios. Integrating steel fibers and fly ash notably enhanced mechanical and shear resistance characteristics, with optimal behavior identified at 50% fly ash content and 1.0% fiber volume. Comparative assessment against prevailing code provisions indicated a trend of underestimation of shear capacity by most existing approaches. An empirical model is proposed, exhibiting excellent correlation with empirical results. Findings affirm the potential of utilizing high-content fly ash as a sustainable fine aggregate substitute in synergy with steel fibers, yielding enhanced structural efficiency and economic advantages.