Flexural Behavior of Steel Fiber–Reinforced Alkali‐Activated Lightweight Aggregate Concrete Superposed Beams: Experimental and Theoretical Study

This study investigates the flexural behavior of six steel fiber–reinforced alkali‐activated lightweight aggregate concrete (SFRAALC) superposed beams and one ordinary Portland cement concrete (OPC) beam through four‐point bending tests. The effects of concrete type, topping thickness, and reinforcement ratio on flexural performance were examined in terms of failure mode, load–midspan deflection response, crack development, ductility, and energy absorption. The results show that SFRAALC beams achieved an ultimate flexural capacity comparable to that of the OPC beam, while exhibiting substantially enhanced post‐yield deformability, resulting in markedly higher overall energy absorption under large strains. Increasing the reinforcement ratio significantly improved load‐bearing capacity but moderately reduced ductility, whereas variations in topping thickness had a negligible influence on overall flexural performance. Furthermore, established design codes like GB 50010‐2010 and ACI 318‐19 provided reliable predictions for the ultimate moment of SFRAALC beams, and a proposed plastic influence coefficient method improved the prediction accuracy of the cracking moment.