Identification Through Seismometric Measurements of Transients Propagating Inside the Asinelli and Garisenda Towers (Bologna, Italy), Implication on Structural Modeling and State of Health Monitoring

Abstract

The SHM has a very important role in the diagnostic process of cultural heritage buildings, for which generally, the identification of the structural behaviour is affected by many uncertainties. The use of ambient vibration tests allow to characterize the dynamic behavior of the structures, providing also information to validate numerical modeling. Moreover, continuous monitoring allows to record streams of seismic ambient noise for long time intervals in order to retrieve the temporal evolution of the structural characteristics and to highlight the response of them to seasonal variations of environmental parameters (temperature, humidity) and the stresses due to the human activities or to the rapid (daily or weekly) changes in the ambient conditions (temperature, wind velocity and intensity). Three seismic monitoring experiments were performed in 2012, 2013 and 2014 at the Asinelli and Garisenda Towers, two masonry leaning tower built in the center of Bologna (Italy). The aim of this work is to present the results of the analysis of the data recorded by seismic monitoring that allowed to clearly identify the normal modes of oscillation of the Two Towers. A particular attention was devoted to the identification of transient that, propagating inside the structures, produce beating effects at the top stations. Implication to the structural modeling and to the State of health monitoring are discussed.