Flexural behavior and design proposals for hybrid steel-BFRP reinforced basalt fiber concrete beams

This study investigates the flexural behavior of basalt fiber concrete (BFRC) beams reinforced with hybrid steel bars and basalt fiber reinforced polymer (BFRP). The experimental program tested twelve hybrid beams, plus two control BFRC beams reinforced with steel bars (steel-BFRC) and two control BFRC beams reinforced with BFRP (BFRP-BFRC) beams, focusing on the effects of reinforcement ratio and basalt fiber content. Results indicate that basalt fibers significantly enhance crack width control prior to steel yielding and slightly improve the cracking moment, deformation capacity, and service-load stiffness of hybrid beams. For an equivalent tensile capacity, hybrid beams developed narrower cracks than BFRP-reinforced beams at all load levels, while exhibiting crack widths comparable to steel-reinforced beams under service loads. Their post-cracking stiffness before yielding was marginally lower than that of equivalent steel-reinforced beams. A numerical model was developed to predict the complete moment-curvature response, flexural capacity, mid-span deflection, and failure modes of hybrid-BFRC beams, showing good agreement with experimental data. Furthermore, theoretical formulas for cracked-section inertia and reinforcement strain were derived, enabling adaptation of ACI 318 and Yoon models to predict effective inertia and crack width in suitably reinforced hybrid-BFRC beams, thereby providing a validated analytical framework for design.