Evaluation of Time-Varying Stress in Prestressed Tendons Based on the Resonance-Enhanced Magnetoelastic Method

Stress in prestressed tendons is crucial for evaluating the health of prestressed concrete (PC) structures. The stress is time-varying due to live loads, and there is a lack of methods to evaluate such stress. In this study, the resonance-enhanced magnetoelastic (REME) method, known for its good dynamic response, was employed to evaluate the time-varying stress. By combining Kirchhoff's circuit law with the magnetoelastic effect, the principle of the REME method was analyzed. The correlation between the induced voltage of the REME sensor and the stress in the prestressed tendon was studied. A time-varying stress monitoring experiment was conducted on prestressed steel strands. The changes in induced voltage with alternating stress and cyclic stress were compared. An alternating stress evaluation method was proposed, and the applicability of the evaluation method to cyclic stress was verified. Based on this, an evaluation method for the time-varying stress in prestressed tendons based on the REME method was proposed. For prestressed steel strands with jacking tension between 50 and 250 kN, when the stress varied by less than 80%, the stress evaluation error was below 10%. This study provides a promising solution for the absolute stress evaluation of prestressed tendons and other ferromagnetic components.