Electromagnetic testing of multi‐strand stay cables: novel technique and instrumentation

Steel stay cables are widely applied in various civil constructions. In recent decades, the so‐called multi‐strand stay cables have become widely used, particularly in the construction of cable‐stayed bridges. Conventional method of stay‐cable diagnostics utilizes magnetic rope testing instruments. However, because of the large diameter of multi‐strand stay cables, the appropriate magnetic instrument should have an inappropriate high mass and create a significant force of attraction between the magnetic head and the stay cable, which likely would cause damage to the cable's outer protective shell. Alternatively, the eddy current method can be used for testing of stay cables. The special probe was developed that provides equal sensitivity to surface and subsurface breaks of the strands and reduces a disturbance of irregularity of magnetic properties along the cable. On the basis of this probe, a specific electromagnetic instrument was designed for nondestructive testing of multi‐strand stay cables. The instrument was tested on a multi‐strand mock‐up and applied for inspection of the stay cables of bridges. Results of this are discussed in the article.