PSI - Issue 64

Donato Fiore et al. / Procedia Structural Integrity 64 (2024) 740–748 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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The antenna beam worth underlining that the interferometric technique provides a measurement of the LOS displacement of all the range bins of the structure illuminates (Fig.3). It should be noticed that interferometry (3) provides a measurement of the radial displacement; hence, the evaluation of the actual displacement requires the knowledge of the direction of motion. For many bridges (simple or continuous spans, frame or truss bridges), the displacement can be assumed as vertical and it can be easily evaluated by making some geometric projection, as shown in Fig. 4.

Figure 4 - Radial displacement and real displacement

To compute the real displacement, the following formula has to be use for each measurement point: = ℎ (4) Where: • d is the real displacement of the i-th measurement point • dr is the measured displacement of the i-th measurement point • R is the distance between IBIS-FS and i-th measurement point. This distance is provide by the system through the range profile • h is the vertical distance of IBIS-FS from the monitored part The machine software IBIS-FS Controller process the acquired data with the geometry information set by the operator. 3. Interferometric Radar Monitoring on Cannavino Bridge Structural Health Monitoring of a construction is the activity of monitoring, verifying and evaluating its structural behavior. Monitoring can be static or dynamic: static monitoring measures displacements while dynamic monitoring measures natural (wind, traffic) or induced vibrations and observers the effects of vibrations on structures. In the case of the Cannavino bridges, terrestrial interferometry technique is used in both static and dynamic configurations. 3.1. System configuration The investigations were conduct using two IBIS-FS systems to obtain an image of both sides of the bridge (Fig. 5a). The first task carried out was to choose the places where to install the two systems. The systems installed considered the following constraints: • the space between the installation points and the monitored elements were to be free from obstacles, such as trees, passage of car traffic, other structures. Subsequently, specific boxes have been equipped. Once the radar systems were positioned, they maintained the same acquisition geometry both in static and dynamic configuration (Fig. 5b)