PSI - Issue 44

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Riccardo Martini et al. / Procedia Structural Integrity 44 (2023) 657–664 Riccardo Martini et al. / Structural Integrity Procedia 00 (2022) 000–000

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Fig. 2. (a) lateral bridge view; (b) deck; (c) seismic isolators.

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Fig. 3. (a) picture of trucks placed over the deck (DT2); (b) plan-view of the accelerometers position.

The bridge is located in a seismic area, therefore, seismic isolators are installed at both the abutments and piers (Fig. 2(c)). On August 4th 2021, the static proof test was performed using different load configurations by placing fully loaded trucks over the deck in specific positions, with the aim to produce severe load conditions on the bridge. In order to determine the dynamic characteristics of the bridge during both the unloaded and loaded phases, the bridge was tested by performing AVTs. For the investigation of the BTI phenomena, two dynamic tests were selected: one referred to the initial unloaded condition of the bridge, the Dynamic Test 1 (DT1), and the second, Dynamic Test 2 (DT2), referred to a load configuration characterized by 10 fully loaded trucks (total mass equals to 440 t), placed over the lateral span of the bridge, as shown in Fig. 3(a). During the DT2, the AVT was performed by placing 3 accelerometers over the first span, as reported in Fig. 3(b); it is worth noting that only the vertical accelerations were recorded, therefore, only the bending and torsional vibration modes can be identified. From the dynamic identification of the unloaded bridge, the frequency value of the first bending mode of vibration is equal to 2.35 Hz. In order to design the static proof tests and to control the loading procedures, the bridge is modelled by using a Finite Element (FE) software (SAP2000). The elastic frame elements are used to represent the I-shaped girders, as well as the cross-beams; the girders are connected to the concrete slab, modelled with thin shell elements, through rigid links taking into account the centroids of each components (Fig. 4a). The hysteretic damping of the system is