PSI - Issue 62

D’Amato Michele et al. / Procedia Structural Integrity 62 (2024) 137–144 D’Amato M. et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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Ofanto rivers (Fig. 1c-d). The geographic context in which such bridges are located presents a strong heterogeneity within the Basilicata Region, including the Lucanian Apennines, the Murge plateau and the Bradanic foredeep. 3.1. River flow interaction Loss of efficiency and functionality of transversal hydraulic structures, stabilizing the riverbed longitudinal profile, can lead to significant morphological changes due to a general scour (Wang et al., 2020). Among the cases analyzed, this situation was observed on the Viaduct I, where the weirs failure (Fig. 2a and Fig. 2b) induced a progressive riverbed lowering, highlighting pier foundations and large boulders along the river reach (Fig. 2c). Foundation exposure resulted in a significant increase in the water impact surface area on the bridge (Fig. 3a), producing the obstruction of the channel due to floating materials and debris (Fig. 3b). This determined local scour processes due to secondary currents and fields of swirling and turbulent flow along the path. a b c

Fig. 2. Viaduct I: (a) Remaining of wing walls of a damaged weir; (b) broken submerged weir placed at the downstream reach; (c) presence of large boulders along the river reach.

Given the multiple intersections between river and bridge, since both have about the same orientation, the H-CoA is assessed in correspondence of the most critical cross-section, where hydraulic hazard for scouring and overtopping was influenced by obstructions and high valley confinement. The general erosion coefficient ( C a ), calculated considering the substructure obstruction width ( W a,l ) and riverbed width ( W a, ) derived from Hydrogeological Plans – PAI (200-year return period), was between 10-15%, resulting in a Medium-Low hazard class. The local scour index (IEF) was greater than 1.2, leading to a High hazard level. Regarding the vulnerability referred to a general scouring phenomenon, the evidence of deep foundations and of general riverbed lowering determined a Medium-Low vulnerability class. On the other hand, concerning local scouring, the evidence of general riverbed lowering with accumulation upstream of bridge piers of debris and floating material resulted in a Medium-High vulnerability class. Therefore, in this case a Medium-High H-CoA was obtained, since the hydraulic vulnerability was the most relevant risk factor. a b

Fig. 3. Viaduct I: (a) Piers foundation exposure upstream; (b) floating material and debris accumulation at bridge piers.

Regarding SF-CoA and S-CoA of Viaduct I, inspections did not provide any significant defect at piers and abutments base. On the contrary, extensive and intense concrete cover detachment with corroded longitudinal bars and stirrups were recorded at the pier caps. Thus, in this case, the deterioration was closely related to improper rainwater disposal from the road deck. On this bridge, the SF-CoA results Medium-High as the SF vulnerability class was affected by Medium-High defectiveness, because of defects detected on pier caps may compromise over time the