Investigation of a Bridge Mechanical Response by a Joint Innovative Impulsive Energizer and a Wavelet Analysis

The monitoring of a wide variety of bridges often requires an approach that, a priori, does not take into account the specific vibrational modes of their structure. An experimental approach to this issue requires to sufficiently energize the structure to allow the detection system to collect the entire range of the structure vibrational modes as well as to characterize their time evolution, also to get information on the structure degradation state. With the aim of monitoring the dynamical response of bridges, the present work addresses an approach based on both a wavelet transform and on an innovative cross-correlation wavelet analysis of the response signals obtained by a traffic-dependent energizer and by an impulsive energizer, where for this latter a new mathematical model has been formulated. The employed devices realize two different stress conditions for the mechanical structure while the wavelet analysis provides the tool for processing the recorded structure response. It is shown that the analysis of a viaduct response, which also includes the cross-correlation wavelet method, makes possible to perform a joint time–frequency analysis for both the cases. Discrete wavelet transform is employed for signal denoising while continuous wavelet transform for detecting signal frequencies and time localization. The performed frequency analyses furnish a common value for the main frequency, i.e. 2.15 Hz for the traffic-dependent energizer and 2.8 Hz for the impulse energizer. The wavelet cross-correlation between the signals produced by the traffic-dependent energizer and by the impulsive energizer, furnishes a diachronic picture of its correlation coefficient.