A multi-technique approach to long-term structural health monitoring of the Garisenda Tower (Italy)

This study presents a comprehensive long-term structural health monitoring approach for the Garisenda Tower in Bologna, Italy, combining multiple non-destructive techniques. Over a 6-year period, data from acoustic emission (AE), fibre optic sensors, and a pendulum system were integrated to assess the tower’s micro- and macro-scale damage mechanisms, as well as global movements. Advanced statistical analyses—such as b-value, Hurst exponent, natural time, and critical fluctuation methods—were applied to AE time series, revealing damage evolution and shifts in structural behaviour around 2023. Results suggest that thermally induced stresses primarily drive damage progression initially, with microcracking strongly correlated to seasonal temperature variations. Post-2023, a transition towards autonomous damage processes was observed, indicating increased instability. The combined data confirm ongoing internal deterioration, emphasizing the importance of multi-technique, long-term monitoring for heritage preservation. Findings support proactive interventions to safeguard this iconic medieval structure against progressive instability.