Tension Estimation in Anchor Rods Using Multimodal Ultrasonic Guided Waves

The diagnosis of post-stressed anchor rods is essential for maintaining the service and ensuring the safety of <i>Electricité de France</i> (EDF) structures. These rods are critical for the mechanical strength of structures and electromechanical components. Currently, the standard method for estimating the effective tension of post-stressed tie rods with a free length involves measuring the residual force using a hydraulic jack. However, this method can be costly, impact the structure's operation, and pose risks to employees. Until now, there has been no reliable on-field approach to estimating residual tension using a lightweight setup. This research introduces a nondestructive method using multimodal ultrasonic guided waves to evaluate the residual tension of anchor rods with a few centimeters free at one end. The methodology was developed through both laboratory experiments and simulations. This new method allows for the extraction of dispersion curves for the first three modes, bending, torsional, and longitudinal, using time-frequency analysis and enables the estimation of the steel bar's properties. Future work will focus on applying this methodology in the field.