On the Use of SAR Data for Structural Monitoring of Bridges: The Case of Albiano-Magra Bridge in Italy

The paper is intended to demonstrate the effectiveness of Synthetic Aperture Radar Interferometry (InSAR) in view of its application for monitoring of bridges and early detection of damages, to prevent collapses and trigger in-situ inspections. A methodology for reconstructing the deformations of a multi-span bridge starting from SAR data is presented, able to derive the vertical and longitudinal components of the mean displacement vectors relative to a certain number of sectors into which the deck is divided, and to distinguish the seasonal deformation from the one induced by any critical issue. The proposed method is applied to the case study of the Albiano-Magra Bridge in Italy, which collapsed on April 8th, 2020. It has allowed to estimate the movements of the bridge deck from 2015 until the date of the last satellite acquisition, a few days before the failure. The results show increasing displacements of one of the side spans in the years before the collapse that are superimposed to the seasonal fluctuations, providing some hints on the possible causes of collapse.