Identifying the tension of prestressed steel strands based on AC impedance at high-frequency currents

In practical engineering structures, particularly bridge structures, the tension of prestressed steel strands is essentially linked to the load-bearing capacity and durability of the structure. Theoretical analysis has demonstrated that the alternating current (AC) impedance generated by the special structure of steel strands in high-frequency AC is related to tension. The mathematical relationship between current frequency, impedance parameters, and tension is established by skin effect. A simulation model of steel strands under high-frequency AC excitation was developed, and the variation trends of impedance values under different tension levels and excitation frequencies were examined. Furthermore, AC impedance measurement experiments were conducted on actual steel strands. Experimental results revealed that the excitation frequency of high-frequency AC affects the sensitivity of AC impedance to tension and its regression accuracy. An optimal excitation frequency range and a method for tension identification were proposed. Under the optimal excitation frequency, when the tension was less than 50 kN, the absolute error of tension identification was less than 13.2 kN; when the tension was more than 50 kN, the absolute error of tension identification was less than 4.6 kN, and the overall relative error was not more than 7.7%.