The Garisenda Tower in 1904: displacement time series

Abstract

In 1904, professor Francesco Cavani, commissioned by the Municipality of Bologna, was tasked with evaluating the stability of the Garisenda Tower. To this end, he developed an innovative monitoring system, based on a plumb line fixed about 40 meters high on the south wall and specialized telescopes, equipped with a double system of lenses and focuses, capable of detecting displacements with precision up to one‐twentieth of a millimeter. The tables attached to his report present in detail the monitoring data, including time series of the eastward and northward displacements, represented at a 20:1 enlarged scale.
In this study, the original series were digitized, scaled, and exported for analysis using modern methods. The goal is to extract information on the dynamic characteristics of the tower’s motion, both in the time domain and in the frequency domain. The results highlight the oscillations and their corresponding amplitudes, providing a modern and updated interpretation of the dynamic behavior of the structure over a century later. This work aims to disseminate basic information on the tower’s behavior in the past, to assess potential significant changes in the kinematic characterization of its movements in future studies. Additionally, future developments are announced to enhance the understanding of the spatial and temporal limits of the results, considering the imperfections of the historical graphs.