Damage detection in a suspension bridge using modal flexibility method

Advances in structural engineering and material technology have resulted in increasing use of suspension bridges in infrastructure systems to satisfy the modern transportation requirements. However, during the long life of a suspension bridge, its main cables and hangers could suffer severe corrosion and fatigue leading to failure of at least a part of the bridge. There is a need for a simple and reliable procedure to detect and locate such damage at its onset so that appropriate retrofitting can be carried out to prevent the failure of these important structural elements. Current Structural Health Monitoring (SHM) systems are integrated with a variety of damage detection methods, which are global and local in nature. Limitations in local methods necessitate the non-destructive and global techniques for damage diagnosis leading to continuous development in vibration based damage detection (VBDD) methods. In this context, this paper develops and applies mode shape component specific damage indices namely; vertical damage index (DIV) and lateral damage index (DIL) based on the Modal Flexibility (MF) concept to detect and locate damage in the main cables and hangers of a suspension bridge. The application of these damage indices is illustrated under single, multiple and complex damage scenarios. Effects of noise in the modal data and higher order vibration modes on the damage detection capability are also captured. Results confirm the applicability of the proposed vertical damage index DIV to accurately detect damage in real suspension bridges using only the first few modes. Bridge engineers can use the proposed technique to monitor the health of suspension bridges and prevent their unexpected failure.