Structural Health Monitoring approaches have been in constant evolution for decades, thanks to advances in sensing technology and computational capabilities. Recent structural collapses around the world stressed out the necessity of having monitoring systems able to identify the health state of structures, particularly for those having a strategic role or historic value, located in highly hazard areas [1]. Extracting dynamic signatures from vibrating structures and inspecting their variations is becoming a popular engineering practice for structural performance assessment and early-stage damage detection [2], whereby a structural damage can be in many cases detected as a modification in the global dynamic behaviour of the structure. This detection of small changes in structural performance, typically produced by earthquakes or by other types of dynamic loadings, allows a cost-effective management of maintenance and restoration interventions [3]. Therefore, an efficient monitoring system, combined with an optimized vibration-based identification approach, allows engineers tracking the dynamic response of the structure, offering the possibility to check its integrity level continuously over time.

In this paper the results of over two years of continuous monitoring of the twin bell towers of the Cathedral of Camerino (Italy) are presented. The monitoring activity target is the evaluation of the dynamic behaviour of the twin belfries after the damages occurred during the seismic events of 2016 and the application of fast securing. The experimental data are acquired in continuous using four triaxial MEMS installed accelerometers, two for each structure, on two opposite corners of the bell cells. Data processing is managed with an automatic system which elaborates the signals and executes Operational Modal Analysis to track the modal characteristics of the structures and their evolution in time. Correlation with environmental factors allows to discern the effect of climatic conditions on the variations of dynamics.

References

[1]  Ubertini, F., Comanducci, G., Cavalagli, N., Pisello, A. L., Materazzi, A. L., Cotana, F., "Environmental effects on natural frequencies of the San Pietro bell tower in Perugia, Italy, and their removal for structural performance assessment," Mech. Syst. Signal Process., 82, 307-322 (2017).

[2] Deraemaeker, A., Reynders, E., De Roeck, G., Kullaa, J., "Vibration-based structural health monitoring using output-only measurements under changing environment," Mech. Syst. Signal Process. 22, 34-56 (2008).

[3]  Saisi, A., Gentile, C., Guidobaldi, M., "Post-earthquake continuous dynamic monitoring of the Gabbia Tower in Mantua, Italy," Constr. Build. Mater., 81, 101-112 (2015).