Wavelet domain analysis for identification of vehicle axles from bridge measurements

Bridge weigh-in-motion (B-WIM) is a process by which the axle and gross vehicle weights of vehicles travelling at highway speeds can be determined from instrumented bridges. The traditional method of attaching strain transducers to the soffit of the bridge and placing axle detectors on the road surface has been replaced here by using additional transducers underneath the bridge for axle detection and nothing-on-the-road (NOR). This paper presents a wavelet based analysis of strain signals and shows the efficacy of using wavelets in pattern recognition of these signals. The transformed signals are used to identify axle passage and hence the vehicle velocity and the axle spacing. In addition to numerically generated strains, signals acquired from such a NOR instrumentation of a bridge in Slovenia have been analysed by the method of wavelet transformation to extract axle position information that was not readily detectable using existing methods.