Characterization of stresses under anchor in prestressing steel strands by contact properties at the anchorage interface

The assessment of the stress state of prestressed steel strands is currently the primary basis for assessing the safety and longevity of prestressed structural systems. In response to the existing lack of efficient techniques for detecting prestressing of steel strands in prestressed girder bridges, the interaction between the anchorage contact interface (specifically the contact interface between the multi-hole anchorage and the anchor bearing plate, MHA-ABP interface) and the ultrasonic signal is investigated experimentally in this study. In addition, the relationship between the contact characteristics of the MHA-ABP interface and the interface pressure is established. Further tests were then carried out on the MHA-MHA interface with one and seven steel strands to investigate the contact characteristics of the MHA-MHA interface under low and high stress conditions. The results show that the reflection coefficient and the non-linear stiffness of the MHA-ABP and MHA-MHA interfaces exhibit a non-linear decreasing correlation with the interface pressure (R_MHA-MHA/ R_MHA-ABP ≈ 1/2.8, K_{1, MHA-MHA}/K_{1, MHA-ABP} ≈ 2.45). Furthermore, linear stiffness and interface pressure follow the theoretical model of a power-law function. The reflection coefficient, linear stiffness and non-linear stiffness show a stabilization with increasing interface pressure. There is a strong correlation between these three indicators and the interface pressure, allowing an effective response to stress variations in the steel strand. This correlation helps to overcome the problem of low accuracy of detection results caused by limitations imposed by the steel strand boundary and other conditions.