Laser Speckle Correlation Method in Diagnostics of Bridge Span Vibrations

Automobile bridge and overpasses are essential elements of transport infrastructure in every country. Rapid diagnostics and subsequent monitoring of critical bridge and overpass components’ performance increases their service life. The aim of this study was to design a method and laser system for remote diagnostics of beam vibrations caused by dynamic loading and to apply them to a laboratory bridge model. The paper discusses a diagnostic method for bridge span vibrations based on laser-speckle correlation together with high-speed video recording. Using a laboratory model of a bridge, bearing structures under shock loading were studied by means of the proposed method. Relative surface displacements induced by different loading conditions were determined herein. The program for calculating correlation functions was optimized taking into account characteristics of the bridge span. In particular, surface displacements were analyzed with regard to the frame frequency and size of laser speckle patterns. Research technique was tested on the laboratory bridge model with beams made of different materials (steel, concrete, wood). For these beams, various shapes and amplitudes of displacements caused by shock loads are shown. Experiments demonstrate remote monitoring of bridge vibration under real shock loads caused by vehicle movement. This will be useful for further development of the proposed technique for bridge vibrations monitoring in real conditions.