Optimizing strength and ductility in reinforced concrete beams using hybrid-FRP laminates

Structural deficiencies in older buildings often require retrofitting or rehabilitation to improve durability and safety. Fiber Reinforced Polymer (FRP) composites are widely used in civil engineering for their effectiveness in restoration, offering superior performance in strengthening and reinforcing structures. This study examines the flexural strength improvement of High Strength Concrete-Reinforced Concrete (HSC-RC) beams using Hybrid Fiber Reinforced Polymer (HyFRP) composites, which combine Carbon-FRP (CFRP) and Glass-FRP (GFRP) laminates. Eight groups of beams underwent four-point bending tests, including both experimental and numerical analyses. One group was a control, while others used either single-layer GFRP or varying HyFRP configurations. The key variable was the arrangement of FRP layers, with beams reinforced by two to five layers of Single/Hybrid FRP composites. Beams with three layers of GFRP increased strength by 37.5% compared to the control, suggesting that beyond three layers, strength gains diminish. Beams strengthened with HyFRP laminates applied to their sides (100 mm wide, 100 mm spaced, and 3000 mm long) showed a 12.5% strength improvement. The optimal configuration was two layers of GFRP and two of CFRP, providing the best balance of strength and ductility, with glass fibers enhancing ductility and carbon fibers contributing to strength. Minimal de-bonding was observed, indicating effective epoxy bonding. Finite Element analysis closely aligned with the experimental results.