Vision-based dynamic monitoring of a steel footbridge

Abstract

The increasing slenderness and lightness of modern footbridges make the vibration serviceability assessment a key aspect for their design and maintenance. A promising approach to the characterization of footbridge dynamic behaviour is represented by computer vision-based techniques. In contrast to traditional monitoring systems relied on dense sensor networks, computer vision-based monitoring requires the installation of one or more cameras together with, if necessary, some targets on the monitored structure. The article presents some preliminary results of the short-term dynamic monitoring of a steel footbridge based on computer vision techniques. The structural deflection caused by a jumping pedestrian was recorded from three cameras in different measurement positions. The post-processing of the video frames is presented and discussed in the article. Special attention is paid to the use of circular targets placed on the footbridge, which allowed for the identification of deflections with sub-pixel resolution. A traditional accelerometer based monitoring system is also installed on the footbridge for validation purposes. Displacements evaluated through a double integration of the measured accelerations are compared to those obtained from the image processing. Results demonstrate the high potential of computer vision-based systems for the monitoring of structures and infrastructures.