Performance of camera-based vibration monitoring systems in input-output modal identification using shaker excitation

A complete dynamic characterisation of structures requires modal frequency, mode shape, modal damping and modal mass to be established for each mode. This can be achieved by using experimental modal analisis (EMA). EMA requires an input force and the resulting structural response to be measured. Optical vibration monitoring systems, enabling remote sensing, could make this process less challenging. This very issue was explored in our latest paper.

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.

Experimental setup

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.

Bridge model

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.

Instrumentation at the driving point

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.