PSI - Issue 62

R. Martini et al. / Procedia Structural Integrity 62 (2024) 392–399 Martini R. et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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Results of the 1 year and half of static monitoring are summarized in Table 2. The dynamic monitoring systems is composed by two 3-axial accelerometers installed on the kerbs in correspondence of the two half-joints. The accelerometers record 30 min-long acceleration time histories 4 times per day (1 every 6 hours) and an AutoOMA is performed to obtain the modal parameters of the Gerber beam (Tomassini et al., 2023). Results of the dynamic monitoring are shown in Figure 5b. In October 2023 the static monitoring system has been slightly modified; specifically, DT4 has been moved from its original position and installed across a crack detected on the half-joint 2, as a result of deterioration of the previous crack pattern. However, in this short period of measurement (Oct. – Dec. 2023), DT4 has detected a very low crack opening (about 0.1 mm in 3 months). Table 2. Measurement of displacement transducers (DT) after 1 year and half of static monitoring (+ is crack opening while – is closing). Displacement Transducer DT1 DT2 DT3 DT4** DT5 DT6 DT7 DT8 Displacement Evolution [mm] +0.50 +0.40 +0.85 +0.60 +0.25 +0.26 +1.00 +0.70 Displacement Evolution [mm] (cleaning temp. effects) * +0.26 +0.16 +0.61 +0.36 +0.01 +0.02 +0.76 +0.46 * The displacement evolutions are cleaned from the thermal dilation/compression of the steel bar used to install the transducers, assuming ΔT = 20°C – ΔL ≈ 0.24 mm. ** The measures refer to the time period June 2022 – October 2023. In April 2023 another experimental campaign was performed with the twofold goal of detecting the crack opening and the vertical displacements of UB deck under heavy vehicle passage. Hence, the displacement transducers were acquired with a higher frequency samples (100 Hz instead of 1 per hour) and their data were put together with data from accelerometers. As a general finding it can be asserted that crack openings due to heavy vehicle passage were very low for all DTs (around 10 -2 mm) and the relevant accelerations were about 2x10 -2 g; moreover, during this campaign, a further DT was installed on the crack of half-joint 2. The latter measured crack openings of magnitude around 10 -4 mm. The vertical displacements were captured through the use of a high-resolution camera installed on the West bank of the river. The maximum deflection measured during a track passage over the half-joint 1 was about 4 mm, in accordance with the vertical displacements measured during the March 2022 static tests. Finally, on December 2023, another comprehensive AVT campaign on DB was performed to obtain once again the modal parameters of the whole bridge to be used as benchmark in the future experimental activities, which are discussed in Section 6. 6. A brief introduction about the experimental in situ campaign planned for the near future Some extensive experimental campaigns, including destructive and non-destructive tests, are scheduled before the demolition of the bridges. The aim of the first experimental campaign, that will be carried out before the demolition of the DB, is aimed to assess the usefulness of non-destructive tests as special inspection tools to gather information about structural features, with particular focus on the pre-stressing system (e.g., material mechanical properties, geometry characteristics, state of damage, residual prestress on cables, etc.). The experimental campaign has been designed and supervised by the same teams of engineers that worked on the bridge inspection and monitoring (UnivPM, UniCAM and ANAS). For what concerns the non-destructive tests, they will be performed on the Gerber beam of the DB and will include tests to gather detailed geometrical information (e.g., laser scanner, georadar, visual inspection), to investigate the prestressing system (ultrasonic tomography, impact echo, covermeter, diffractometric, hardness, and corrosion tests, as well as stress release tests on cable wires and concrete), and to define the mechanical properties of materials (core samples on concrete and steel samples, pull-out tests). Furthermore, dynamic tests by using accelerometers are also planned. A second experimental campaign will be probably developed on the second deck to be demolished (UB), to characterise the behaviour of the half-joints up to collapse and to investigate the effectiveness of dynamic monitoring systems to capture damage artificially induced in the pre-stressing system.