Behavior of Reinforced Concrete Columns Strengthened with FRP: A State-of-the-Art Review

Structural columns often require strengthening due to deterioration, increased load requirements, or structural modifications, and their complete replacement prior to the end of their design life is economically impractical. Rehabilitation of Reinforced Concrete (RC) columns using modern materials, such as Externally Bonded (EB) Fiber-Reinforced Polymer (FRP) composites, is widely used. Similarly, Near-Surface Mounted (NSM) FRP is an effective and reliable technique for improving column load-carrying capacity while preserving the architectural profile of the structure after strengthening. The main aim of structural strengthening is to increase the ductility and ultimate strength of RC columns, increase their load-carrying capacity, and minimize the risk of damage or failure under increased service loads while ensuring structural compatibility. This paper reviews the latest research and developments on the performance and behavior of RC columns strengthened with FRP under various loading conditions and key operational parameters, such as cross-sectional geometry, slenderness, and eccentricity. Overall, the review highlights that combining longitudinal NSM strengthening with transverse EB-FRP confinement yields superior structural performance by mitigating premature debonding, enhancing flexural rigidity, and optimizing strain distribution across non-uniform stress gradients. Based on a comprehensive review of experimental and numerical studies, structural strengthening. using FRP composites yields distinct quantitative improvements depending on the technique employed, full EB-FRP wrapping increases axial capacity by 25%–110% under concentric load and 35%–90% in damaged short columns, while NSM systems enhance flexural capacity by 38%–72% and energy dissipation up to 120%. Under eccentric loading, axial gains diminish to 8%–33%. Hybrid FRP systems (NSM combined with EB wraps) yield peak capacity gains of 49%–95% and restore up to 100% of original. strength in pre-damaged columns, effectively delaying debonding