Application of Vision- based Monitoring System to Stay Cables

Stay cables as a critical member of cable-stayed bridges are an important element for supporting the entire structure. They would be vibrated due to various reasons and such vibration has been often investigated in many existing bridges. Thus, current studies on verification of its mechanism and measures for vibration control have been actively progressed. It is also required to verify the influence of cable vibration by health monitoring because cable vibration leads cable fatigue and visual anxiety of drivers. Accelerometers, as one of the conventional sensors being used to measure stay cable vibration of existing bridges, may not easy to install at stay cables and require the considerable cabling work to facilitate a direct connection between each sensor and instrument. For this reason, a technique using digital image processing, which is one of non-contact sensing systems, may be needed to detect cable vibration affecting bridge structures. In this study, a method is suggested to measure vibration of multiple cables using image processing techniques and a vision-based monitoring system, as a sensing system to measure cable vibration remotely considering convenience and economic aspects for use, has been developed. In the developed vision-based monitoring system, a remote controlled pan-tilt drive is installed to measure a number of cables with a camera. The developed system ensures the resolution on remote cables using a 20x optical zoom lens. This study has been applied to a cable-stayed bridge pylon, Busan-Geoje fixed link located in South Korea, to verify the validity of the method which could measure the vibration of stay cables using the developed system.