Numerical Investigation of the Structural Behavior of Reinforced Concrete Deep Beams Strengthened with Fiber Reinforced Polymer (FRP) Reinforcing Bars Using the Finite Element Method

Fiber-reinforced polymer (FRP) reinforcement has emerged as an important alternative to conventional steel due to its high corrosion resistance and long-term durability. However, studies on the behavior of FRP-reinforced concrete deep beams under shear-dominated conditions remain limited. In this study, the structural behavior of reinforced concrete deep beams strengthened with GFRP and CFRP bars was numerically investigated using the ABAQUS finite element software. A parametric analysis was conducted to evaluate the effects of shear span-to-depth ratio (a/d), concrete compressive strength, tensile reinforcement ratio, and reinforcement type. The results indicate that reducing the a/d ratio from 1.4 to 1.12 increased the maximum load capacity by 37.6% for GFRP beams and 10.0% for CFRP beams, reflecting enhanced arch action. Increasing concrete strength from 25 MPa to 40 MPa led to capacity increases of 64.5% (GFRP) and 41.7% (CFRP), confirming its dominant role. Increasing the reinforcement ratio improved capacity by 6–9% in GFRP systems and over 15% in CFRP systems. CFRP-reinforced beams exhibited 20–55% higher load capacity, while GFRP beams showed greater ultimate displacement (13–18 mm vs. 8–12 mm). Overall, CFRP provides superior strength, whereas GFRP offers enhanced ductility, supporting performance-based design.