PSI - Issue 62

R. Martini et al. / Procedia Structural Integrity 62 (2024) 392–399

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Martini R. et al. / Structural Integrity Procedia 00 (2019) 000 – 000

5. Test campaigns and monitoring during the life cycle of the two bridges The two bridges have been object of several test campaigns during the last 2 years, performed by UnivPM and UniCAM with the support of ANAS. A summary of the whole experimental campaign is reported in the right-hand side of Figure 1. The first experimental campaign dates back to March 2022; indeed, after the visual inspections revealing the high deformability of the DB, it was decided to perform static and dynamic tests to better understand the behaviour of both bridges and to collect data to support decisions on their usage. The static test was done on DB and consisted in stationing a loaded truck (33.5 t heavy) in 5 different locations of spans 3, 4, and 5, and in measuring the deck deflections on 3 cross-sections (in correspondence of the 2 half-joints and at midspan 4). The maximum vertical deflections were measured at the half-joint cross-sections where displacements of about 3.4 and 3.2 mm for half-joint 1 and 2 were reached, respectively, when loaded directly by the truck. It is worth mentioning that deflections showed important residuals so that it was difficult to interpret results obtained from the different loading configurations. Dynamic tests consisted of a very accurate dynamic identification through Ambient Vibration Tests (AVTs) of both bridges, and in the recordings of the deck vertical accelerations during the truck passage on the bridges at a constant speed of 80 km/h. The dynamic identification, performed by using Operational Modal Analysis, (OMA) allowed the identification of the first two global vibration modes to be done, whose modal parameters are reported in Figure 4. By using acceleration recordings during the truck passages (with maximum value around 0.07 g) it was possible to obtain an estimation of damping ratio related to the 1 st vibration mode by adopting the logarithmic decrement method, which was about 1.27% for UB and 1.53% for DB. These two values are higher than those obtained from OMA (at least for DB) because of the higher level of acceleration experienced by the bridges during the truck passages, which can activate local and global dissipative mechanisms (e.g., friction between cracks, small movement of supports, etc.). However, it is worth remembering that during AVTs, DB was closed to traffic, while UB was open. Then, in June 2022, a permanent static and dynamic monitoring system was installed on the UB, which is open to traffic (Figure 5a). The static monitoring system consists of 8 displacement transducers (DTs) mounted on the lateral side of the box-girders in correspondence of the two half-joints to measure a possible widening of cracks. One measure every hour is collected by each transducer.

Figure 4. Modal parameters of both bridges from OMA performed on March 2022.

Figure 5. Static and dynamic permanent monitoring system: (a) system layouts, (b) results of the dynamic monitoring.