Prestress evaluation of steel strands based on interwire energy dissipation of longitudinal guided waves

Accurate evaluation of the prestress of steel strands is crucial for ensuring the safety of structures such as cable-stayed bridges and prestressed concrete bridges. Ultrasonic guided waves, with low attenuation and long propagation distance capabilities, have been introduced for the prestress evaluation of steel strands. However, the complex helical structure of the peripheral wires causes mode aliasing and multipath interference of the guided waves, affecting the reliability of the evaluation results. Therefore, this paper adopts a central straight wire single-path excitation-reception strategy to ensure the mode purity and path clarity of guided wave propagation. And based on this strategy, a dimensionless Prestress Evaluation Index (PEI_E) is further proposed. First, the energy dissipation mechanism of longitudinal guided waves caused by friction contact between steel wires was analyzed theoretically. Subsequently, tension tests were conducted on steel strands to validate the feasibility of the PEI_E-based method for prestress evaluation. Additionally, numerical simulation methods were employed to improve the amplitude and energy attenuation models of longitudinal guided waves propagating along the central straight wire under prestress. The results indicate that the amplitude and energy of guided wave signals decrease linearly with prestress, while the PEI_E shows a linear increase with prestress. The optimal agreement between simulation and experiment is achieved with an interwire friction coefficient of 0.1, as evidenced by the minimal relative deviations in the linear fit (8.76% for slope, 6.06% for intercept) of the PEI_E-prestress relationship. Both the amplitude and energy attenuation coefficients increase linearly with increasing prestress. The improved attenuation models accurately characterize the attenuation behavior under the coupling effect of propagation distance and prestress, with determination coefficients of 0.9932 (amplitude) and 0.9935 (energy). The established prestress-propagation distance two-variable PEI_E model lays the foundation for the quantitative evaluation of prestress in steel strands.