Application of guided waves for damage monitoring in multi-wire cable structures

Multi-wire cable structures are widely used in civil engineering applications such as stay cables in suspension bridges, elevators and overhead electric transmission lines. The loss of cable load and presence of cable breakage can be catastrophic for the entire structure. Various techniques have been applied to the non-destructive monitoring of structural health of multi-wire cable structures. However, few of them could fully characterize the early structural degradation or reliably determine the damage mechanism due to the limited access to structural components and other environmental factors. In this thesis, a guided wave-based structural health monitoring system that is capable of monitoring the cable load levels and detecting defect simultaneously is developed for multi-wire cable structures. A series of finite element analysis were conducted using Abaqus/Explicit to explore the feasibility of using ultrasonic guided waves to detect the notch in multi-wire cable structures, followed by the experimental verification on a seven wire strand. Both numerical studies and experimental works presented in this research have revealed that guided waves could be a promising technique for defect detection in multi-wire cable structures. On the other hand, finite element analyses were conducted in this study to investigate the nonlinear characteristics of ultrasonic guided waves in a multi-wire cable under different preloaded levels. The wave signals after a fast Fourier transform indicate that second harmonic peak together with the calculated nonlinear parameters decreased as the preload level increased. The corresponding wave energy was integrated to minimise the adverse influence caused by dispersion and multimodality during wave propagation. The results revealed a similar trend, which demonstrated the feasibility of ultrasonic guided waves to monitor the load level in multi-wire cable structures.