Numerical and theoretical investigation for the flexural behaviour of geopolymer concrete beams reinforced with hybrid FRP /steel bars

Recent studies have demonstrated the effectiveness of Fibre Reinforced Polymer (FRP) and steel bars as longitudinal reinforcement for Geopolymer Concrete (GPC) beams. However, research on the combined performance of these materials in hybrid FRP/steel-reinforced GPC (HRGPC) beams remain limited. This study addresses this gap using finite element (FE) analysis with ABAQUS software and theoretical modeling, validated against available experimental data, to investigate the flexural behaviour of HRGPC beams. The results showed strong agreement between FE analysis and experimental findings regarding failure modes, load-deflection, and load-strain response. Parametric studies revealed key factors influencing flexural performance, including compressive strength, reinforcement ratio, FRP reinforcement type, and the presence of openings. Compressive strength showed a limited effect on flexural behaviour, so doubling it from 30 to 60 MPa resulted in only a 12 % increase in load capacity due to steel bars yielding. The results showed a significant impact on the ratio of FRP to steel bars (Af/As ). A 50 % GFRP and 50 % steel bar combination increased load capacity by 12.3 % compared to steel-only reinforcement. Additionally, HRGPC beams exhibited lower deflection than those reinforced solely with FRP bars. Theoretically, the load capacity was predicted using theoretical models developed by Qu et al., Safan, and Yang et al., giving conservative results. Therefore, a new equation was developed to come up with a better estimation of the load capacity of geopolymer concrete beams reinforced with hybrid reinforcement (FRP and steel), providing a mean value, standard deviation, and coefficient of variation of 0.91, 9 %, and 10 %, respectively.