Vibration Monitoring of Multiple Bridge Points by Means of a Unique Vision-Based Measuring System

Bridge static and dynamic vibration monitoring is a key activity for both safety and maintenance purposes. The development of vision-based systems allows to use this type of devices for remote estimation of a bridge vibration, simplifying the measuring system installation. The uncertainty of this type of measurements is strongly related to the experimental conditions (mainly the pixel-to-millimeters conversion, the target texture, the camera characteristics and the image processing technique). In this paper two different types of cameras are used to monitor the response of a bridge to a train pass-by. The acquired images are analyzed using three different image processing techniques (Pattern Matching, Edge Detection and Digital Image Correlation) and the results are compared with a reference measurement, obtained by a laser interferometer providing single point measurements. Tests with different zoom levels are shown and the corresponding uncertainty values are estimated. As the zoom level decreases it is possible not only to measure the displacement of one point of the bridge, but also to grab images from a wide structure portion in order to recover displacements of a large number of points in the field of view. The extreme final solution would be having wide area measurements with no targets, to make measurements really easy, with clear advantages, but also with some drawbacks in terms of uncertainty to be fully comprehended.