One-year dynamic monitoring of a historic tower: damage detection under changing environment
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The paper summarizes the conceptual development of a vibration-based strategy suitable to the structural health monitoring of ancient masonry towers and exemplifies its application in the continuous dynamic monitoring of the tallest historic tower in Mantua, Italy. The presented approach is based on the installation of low-cost monitoring systems (consisting of few accelerometers and temperature sensors) and on the combined use of automated operational modal analysis, regression models to mitigate the environmental effects on identified natural frequencies and multivariate statistical tools to detect the occurrence of abnormal structural changes. The application of the adopted strategy to 15 months of continuously collected experimental data: (1) highlighted the effect of temperature on the automatically identified natural frequencies; (2) demonstrated the practical feasibility of damage detection methods based on natural frequency shifts; (3) provided a clear evidence of the possible key role of continuous dynamic monitoring in the preventive conservation of historic towers.
KeywordsAutomated modal identification Continuous dynamic monitoring Earthquake Environmental effects Masonry towers
The authors would like to commemorate Prof. Francesco Benedettini, a great Italian scholar of Structural Dynamics at the University of L’Aquila. The memory of his friendship and enthusiastic energy will never disappear. The research was partially supported by the Mantua Municipality. M. Antico, M. Cucchi (VibLab, Laboratory of Vibrations and Dynamic Monitoring of Structures, Politecnico di Milano) and Dr. Lorenzo Cantini (Dept. ABC, Politecnico di Milano) are gratefully acknowledged for the assistance during the field tests and the maintenance of the monitoring system.
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