Non-contact measurement of vibration modes of large cable-stayed bridge under ambient conditions: a convenient way of condition monitoring of bridges

Non-contact vibration measurement of civil engineering structures is one of the most emphasized areas in structural health monitoring. Conventional methods have many limitations and challenges when used for the vibration testing of large civil engineering structures. Devices such as accelerometers must be mounted at appropriate locations to be able to record structure's motion, which can pose a major accessibility issue. Laser-based far-field displacement measurement systems that can only measure motion in the direction of the laser beam also require mounting of reflectors at the point of interest. Other limitations include upper and lower frequency limits and greater inaccuracies at higher frequencies, higher cost and multichannel applications for plotting mode shapes are impractical. In this research, a previously validated microwave interferometric radar is used for taking the response of cable-stayed bridge under impact and ambient conditions. The apparatus namely VirA can image the target in 3-dimensions from a single point of measurement with a least count of <= 0.1 mm. The accuracy of VirA was checked by the identification of lower-order modes of vibrations of the main girder. Several stay cables were then measured to identify natural frequencies for potential use in the condition monitoring of the bridge. VirA was found to be reliable in the measurement of natural frequencies of different structural components. Lower modes of vibrations were identified but mode shapes showed variation. Lower-order natural frequencies for cables were identified by VirA which suggests that it may be used for condition monitoring of cable-stayed bridges.

Automated summary

Non-contact vibration measurement is a crucial aspect in structural health monitoring, but conventional methods face limitations and challenges when applied to large civil engineering structures. This research utilized a microwave interferometric radar called VirA to measure the response of a cable-stayed bridge and found it to be reliable in identifying the natural frequencies of various structural components, indicating its potential for condition monitoring of cable-stayed bridges.