Preliminary Interpretation of the Data from the Static Long-Term Monitoring System on the Asinelli Tower in Bologna, Italy

Structural Health Monitoring plays a very important role in the diagnostic process of existing structures, and especially for historical and cultural buildings, whose structural behaviour is generally affected by significant uncertainties that render each structure “unique”. If properly associated to an extensive knowledge of thematerials and the structural layout, it represents an important tool to obtain precious information regarding the time-evolution of some significant response parameters and thus estimate the future behaviour of such buildings, also helping the owners in management and "decision making" activities for maintenance and interventions. The inherent complexity of historical buildings, together with the natural material decay and the effects of natural and anthropic hazards (extreme weather events, earthquakes, traffic vibrations, etc.), make the assessment of their “structural health” not only extremely challenging but also actually essential for their conservation. In this respect it is fundamental to monitor their conditions, to know the time evolution of their safety level, in order to implement economic and efficient retrofit interventions. In this paper, an example of the application of the Principal Component Analysis (PCA) on the data collected by the SHMsysteminstalled on theAsinelli Tower in Bologna (Italy) in the last decade is presented. This allows to assess the main information hidden in the recorded data, to identify the evolving trend of some response parameters, and to compensate the effects of the temperature. The methodology applied in this paper might be useful in the future monitoring activities in the development of threshold values for the assessment of sound and reliable safety levels of the Tower.