PSI - Issue 84

Michela Pulsoni et al. / Procedia Structural Integrity 84 (2026) 214–222 M. Pulsoni et al. / Structural Integrity Procedia 00 (2026) 000–000

218

5

The first step of a monitoring campaign is to select suitable measurement positions; since only the displacement component along the radar line of sight is measured, at least two radar locations with different viewing geometries are generally recommended. For continuous monitoring (static and dynamic analyses), the system is installed on a permanent platform, while for short-term campaigns it is usually mounted on a tripod; in both cases, mechanisms for azimuth and elevation adjustment are required. Because TInRAR is sensitive only to displacement components aligned with the instrument line of sight, when multiple motion directions or simultaneous three-direction measurements are needed and additional TInRAR units are not available, the survey can be complemented with accelerometers or velocimeters in contact with the structure, providing information on vibration frequencies along directions orthogonal to the radar line of sight. The main acquisition parameters in dynamic TInRAR monitoring are: • Maximum acquisition range: set slightly larger than the distance to the farthest point of the structure, to avoid information loss in distant sectors while limiting data volume. • Sampling frequency (PRF): at least twice the highest expected vibration frequency, according to the Nyquist criterion, noting that higher PRF values greatly increase data volume and processing time and may be constrained by the selected range. • Acquisition duration: typically 15–30 minutes per each monitoring position, generally sufficient under natural excitations such as wind and environmental loads • Range resolution: preferably the highest available (around 0.75 m), to maximise the number of measurement points on the structure and obtain the description of dynamic behaviour. 3. Case studies 3.1. Survey and monitoring of the Puleto and Tevere IV viaducts along the E45 (Tuscany) In the period 4–9 February 2019, as part of the monitoring activities on the Puleto and Tevere IV viaducts along the E45, an integrated survey and monitoring campaign was carried out on the road section including the two viaducts. The activities included: • Visual inspections by means of an Unmanned Aerial Vehicle (UAV), aimed at documenting the condition of piers, bearing systems, girders and decks. • Characterization of the static and dynamic deformation behaviour using a terrestrial interferometric radar system, performed on both viaducts. • Interferometric methodology (TInRAR). For the characterization of the deformation behaviour, the TInRAR technique was employed. This method enables the simultaneous measurement of displacements at numerous points of the investigated structure along the line of sight (LOS), in a differential way, by comparing the phase information of the electromagnetic wave emitted and reflected by the sensor at different time intervals. This approach allowed the reconstruction of: • The frequency spectra associated with the dynamic response of the viaducts. • The displacement time series at the monitored points. The interferometric sensor used was an IBIS-S, manufactured by IDS S.p.A specifically configured for the monitoring of linear structures such as viaducts and bridge decks. The monitoring geometry adopted, including the sensor location, the monitored targets, and the main distances and viewing angles, is shown in Errore. L'origine riferimento non è stata trovata. . This configuration made it possible to capture multiple spans of the viaducts simultaneously, thereby maximising both the number of measured points and the quality of the deformation information.