Experimental and Reliability Analysis of Flexural Performance of CFRP Strengthened Damaged Reinforced Concrete Beams

The use of fiber-reinforced composite materials for the reinforcement and repair of reinforced concrete (RC) structures offers several technical advantages, including lightweight properties, high strength, and ease of construction. This paper presents a bending performance test on RC beams that are close to yielding damage, utilizing carbon fiber cloth for reinforcement. The study explores and analyzes the bending load capacity, short-term stiffness, and reliability of damaged RC beams strengthened with carbon fiber cloth. Key factors influencing the bending load capacity of these damaged concrete beams include the height coefficient of the compression zone, steel reinforcement ratio, utilization factor of carbon fiber cloth strength, and failure modes. A calculation method is proposed for determining the bending load capacity of cracked damaged RC beams after unloading with carbon fiber cloth reinforcement; this method demonstrates high accuracy. Considering initial loading conditions, we analyze the variation in sectional stiffness due to carbon fiber cloth reinforcement in damaged concrete beams and establish a simplified calculation formula for their short-term stiffness. The reliability of reinforced damaged RC beams is related to factors such as the amount of reinforcement applied, elastic modulus of carbon fiber cloth, and performance indicators associated with its guaranteed strength values. Results indicate that applying carbon fiber cloth can effectively enhance the bending load capacity of damaged RC beams. Furthermore, as additional layers are added during strengthening processes, both bending load capacity and short-term stiffness increase progressively. The results from our proposed calculation formulas align well with experimental values while maintaining high precision. Utilizing structural reliability theory methods through calculations analyzing reliability indices reveals that reinforcing damaged RC beams with carbon fiber cloth significantly improves their reliability metrics. When Mk loading approaches My during unloading strengthening-while keeping other factors constant-the reliability index gradually increases alongside improvements in both performance indicator values related to guaranteed strength levels and additional layers used in strengthening efforts.