A novel damage index based on ultrasonic signal dissipation for damage assessment in strengthened columns

Purpose This study investigates damage evolution in concrete columns strengthened with a thin polypropylene fiber-reinforced concrete (PPFRC) jacket through ultrasonic wave dissipation analysis under cyclic loading. Full-scale specimens underwent constant vertical loading and alternating horizontal forces until failure. Damage progression was evaluated using a proposed model based on variations in ultrasonic signal energy, quantified by a damage index (DI). The model demonstrated strong alignment with established methods, confirming its validity. Polypropylene fibers significantly improved column performance, enhancing ductility, resilience and the effectiveness of structural reinforcement. Design/methodology/approach Reinforced concrete columns were strengthened with a 50 mm thick PPFRC jacket and subjected to cyclic loading. Damage progression was monitored using ultrasonic testing and a DI based on energy dissipation. The model's validity was confirmed by comparison with established methods. The use of PPFRC resulted in significant improvements in ductility, resilience and overall structural performance, demonstrating the effectiveness of the PPFRC reinforcement. Findings (1) The used approach enabled the development of a new DI model, which reflects changes in the damage state and material degradation over time, allowing for real-time monitoring and early detection of structural failures. (2) Thin jacketing with FRC significantly enhanced the load-bearing capacity, ductility and seismic performance of the columns. This repair method strengthened the bond between cracks, improved the structure's robustness and increased its fatigue resistance, addressing the brittle behavior of non-fibered concrete. Originality/value (1) A new DI model has been proposed. (2) An effective reinforcement technique using a PPFRC jacket has been proposed.