Assessment of metal strand wire pre-stress in anchor head by ultrasonics

Pre-stressed strand wires 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 simulations are conducted on the anchor head. The wave amplitude, transit time and other characteristics are influenced by the stress of the strand wires which affects the contact between wires, wedges and the surrounding matrix of the anchor head. The change of contact pressure between the strands and anchor head is simulated by modifying the rigidity of a model interphase material. The results are compared with experimental measurements on the same geometry of anchor head and different pre-stress levels. Therefore, a practical nondestructive inspection method to assess the pre-stress level of the strands is discussed.