Wave propagation in anchor head for assessment of metal strand pre-stress

Pre-stressed steel strands embedded in a structure is a common way to reinforce the weak tensile nature of concrete or soil materials. Due to corrosion, the strands may lose the pre-tension with disastrous consequences. The accessibility to the strands is usually limited to the anchor head from where the assessment should be done. In this paper, through the thickness elastic wave measurements are conducted on the anchor head. The wave amplitude, delay time and other characteristics are influenced by the stress of the strands which affects the bond between strands, wedges and the surrounding anchor head. Numerical simulations are also conducted verifying that the stress of the strands strongly influences the wave parameters. The change of bonding between the strands and anchor head is simulated by modifying the rigidity of a model interphase material. Therefore, a practical non destructive inspection method to assess the pre-stress level of the strands is discussed.