A metric of giving an overview of mechanical damage has been proposed to practically realize the structural health monitoring of mechanical system using IoT data. In the case that a mechanical system includes many local hot spots, such as welded and bolt joints, where structural health should be monitored, the health monitoring system for all spots could be a large and expensive one. To overcome this drawback and increase the number of machines under structural health monitoring, the concept of

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... a hierarchical monitoring was applied to the structural health monitoring of wind turbines in this development. In the first stage of the hierarchical monitoring, an overview of mechanical damage is given using the proposed metric, and accordingly, target machines are extracted for additional monitoring. The local damage can be accurately evaluated at the hot spots in the additional monitoring. As the result of employing the metric of giving the overview for several wind turbines, the extracted turbines corresponded to the turbines that are operated under severe wind conditions and expected for the accumulation of mechanical damage. It can be therefore concluded that the concept of the hierarchical monitoring is effective to the expansion of the monitoring target.