Vision-based approach for the static and dynamic monitoring of bridges

Structural Health Monitoring (SHM) is one of the main approaches to deal with damage identification in existing bridges. Static information together with structure modal properties allow to prevent collapses, detect damage also in the early stage, and plan maintenance works based on the bridge condition. Measurement systems are traditionally composed of a network of sensors directly installed on the structure. Despite the large diffusion of these systems, the expensive and time-consuming installation of sensors and acquisition system makes their use not always feasible. A promising approach for the characterization of bridge dynamic behavior is represented by computer vision-based techniques, which require the sole installation of one or more cameras outside the structure, along with some targets on it when necessary. This approach is totally non-invasive, low-cost and enables the direct measurement of structural displacements, providing useful and direct information about the operational conditions and possible permanent deformations. With the aim of investigating the potential of vision-based techniques for the dynamic monitoring of structures, this paper presents preliminary results of dynamic tests performed on a steel footbridge. Structural vibrations caused by a jumping pedestrian were measured from a camera placed at the riverbed as well as by an accelerometer-based monitoring system installed for validation purposes. The post-processing of video recordings is here presented and discussed, with particular emphasis on the impact of target shape and camera shaking.