## 1 Introduction  
Reinforced concrete (R/C) structures are widely used in civil engineering due to their high strength and ductility. However, despite these advantages, R/C structures are prone to long-term degradation caused by factors such as environmental exposure, aging, and seismic activity. These factors can compromise the structural integrity of R/C structures, making strengthening essential to prolong their service life and ensure safety, particularly in the aftermath of seismic events. Among the various strengthening methods, fiber-reinforced polymer (FRP) composites have gained significant attention due to their high strength-to-weight ratio, excellent corrosion resistance, and ease of installation. Interest in using FRP for structural strengthening began to grow in the early 1990s. In particular, analytical studies in these years have paved the way for their use in strengthening R/C members by contributing to the improvement of these methods [1; 2; 3; 4]. FRP strengthening methods significantly improve the mechanical performance of R/C structures, increasing their load-carrying capacity and resistance to cracking under both flexural and shear stresses. Today, FRP composites are widely regarded as an ideal solution for strengthening R/C members, especially in seismic regions, thanks to their flexibility, durability, and ability to significantly enhance structural performance [5; 6; 7; 8; 9]. FRP is typically used to strengthen or rehabilitate R/C beams through two main techniques. The first involves externally bonding FRP sheets or strips to the surface of the concrete, while the second involves embedding FRP rods into grooves cut into the concrete surface, a method referred to as the Near-Surface Mounted (NSM) technique [10; 11; 12; 13; 14; 15; 16]. Although NSM is proposed as a way to improve bond strength and mitigate issues such as premature debonding, it presents significant challenges in terms of installation complexity and cost. Furthermore, the difficulty of ensuring accurate placement in NSM applications makes it less practical for many real-world strengthening projects [17]. In contrast, externally bonded FRP strips offer a far simpler and more cost-effective solution, with easier application and proven effectiveness in enhancing the structural performance of R/C elements. Despite the advantages of FRP, experimental and numerical studies have shown that this strengthening technique can also introduce brittle failure mechanisms, such as debonding of the FRP, which diminish its effectiveness and reduce the overall stiffness of the structure. [PERSON] [18] examined the deformation behavior and stiffness characteristics of R/C beams strengthened with carbon fiber-reinforced polymer (CFRP) strips under various load levels. The research focuses on how CFRP strengthening affects the beams' load-bearing capacity, stiffness, and displacement patterns. Experimental results demonstrated that the application of CFRP significantly enhances the load-bearing capacity of R/C beams while reducing the displacement and hence the ductility. [PERSON] et al. [19] investigated the flexural behavior of pre-damaged R/C beams strengthened with CFRP. A total of 25 R/C beams were tested, considering different pre-damage levels, shear span-depth ratios, and CFRP thicknesses. The primary objective was to understand how CFRP strengthening affects the load-carrying capacity, stiffness, and failure modes of R/C beams subjected to progressive damage. The results demonstrated that CFRP significantly improves the flexural load capacity of pre-damaged beams, with minimal influence from the initial damage levels. However, the shear span-to-depth ratio plays a crucial role in determining failure modes, transitioning from intermediate crack debonding to cover separation near the CFRP end as the ratio decreases. Furthermore, adding more CFRP layers enhances the load-bearing capacity in some cases but may reduce ductility depending on the failure mode.