PSI - Issue 64

Dario De Domenico et al. / Procedia Structural Integrity 64 (2024) 784–790 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 3. Comparison between experimental (top) and numerical (bottom) mode shapes for the first three modes of the overpass deck.

5. Conclusions In this contribution, the structural health assessment of a series of road overpass decks, part of the A20 highway (Sicily, Italy), has been discussed. The peculiarity of these structures consists in the Niagara-type Gerber static scheme. In the context of vibration-based monitoring approaches, recordings from an extensive campaign of dynamic free vibration load tests have been processed via a VMD-based approach and interpreted to properly identify the modal parameters for each one of the investigated structures. The reliability of results from dynamic field tests has been assessed by comparing them with an accurate FE numerical model, properly tuned based on an experimental campaign for material characterization performed on the same structures. Further, exploiting the information from the original drawings as well as parametric analysis, the most suitable boundary conditions for the FE model have been determined. With regard to the findings from dynamic tests, the first two mode of vibrations are associated with the flexural and torsional vibration of the central span, whereas the third mode is associated with vibrations occurring also in the cantilevered spans. This vibration behavior, which is quite peculiar and different from that observed in simply supported or continuous girder bridges, is representative of Niagara-type Gerber schemes that were widely in the last century for realizing road overpasses in Italy. Damping ratios identified from the tests agree with typical values in serviceability conditions observed in prestressed concrete bridge decks with similar span lengths. The results from the dynamic tests were analyzed in conjunction with static load tests performed on the same road overpasses under the traffic load models of the Eurocode 1 part 2 (here not discussed for brevity). It has been concluded that the analyzed overpasses do not present any relevant damage or cracking process under serviceability conditions, since negligible fluctuations both in frequency and mode shapes are observed with respect to the FE simulations assuming ideal material properties, and experimental deflections are consistent with numerical estimates obtained by the FE model equipped with stiffness characteristics of the undamaged scenario.