The application of camera-based vibration monitoring systems in EMA remains largely unexplored for bridges and other large-scale structures. However, their application could offer savings in the cost and time of EMA campaigns, as a camera can capture structural response at multiple points and the deployment of these systems does not require direct access to the tested structure.
To this end, as a part of PhD project conducted by Maksat Kalybek, we set out to characterise the dynamics of a model of cable-stayed bridge by means of a vibration monitoring system consisting of a consumer-grade camera and two open source image processing algorithms. Two types of excitation signals fed into a shaker (i.e. vibration exciter) were tested – sine chirp and pseudo random, each delivered at two levels of intensity. The performance of camera-based vibration monitoring system was compared to the system based on wired accelerometers.
For the particular application we tested, we found camera-based MCS capable of delivering measurements of quality sufficient for the experimental modal analysis. The optic flow tracking algorithm consistently outperformed the template matching tracking algorithm and the pseudo ramdom excitation consistently outperformed the sine chirp excitation. The importance of the signal length and signal processing was highlighted, and suitable stabilisation diagrams of modal properties were found to reduce modal identification uncertainties.
Overall, the results of this study encourage wider utilisation of camera-based vibration monitoring systems in engineering practice and motivate efforts to fully exploit the high-end information (i.e. by deriving modal damping and mass), apart from the modal frequencies and mode shapes typically reported.
The paper reporting the results from our study is freely available here:
Kalybek, M., Bocian, M., Pakos, W., Grosel, J. and Nikitas, N., Performance of camera-based vibration monitoring systems in input-output modal identification using shaker excitation , Remote Sensing 13(17), 2021, 3471.
You may also be interested in one of our recent papers exploring EMA in which input force is delivered with an instrumented hammer:
Kalybek, M., Bocian, M. and Nikitas, N., Performance of optical structural vibration monitoring systems in experimental modal analysis, Sensors 21(4), 2021, 1239.