PSI - Issue 84

Michele D’Amato et al. / Procedia Structural Integrity 84 (2026) 536–543

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degrees of generalized and localized scour phenomena. Whereas, in the case of M bridge piers, 15 cases of scour are identified. Regarding the geometric parameters, an initial analysis is conducted to determine the pier shapes most exposed to scour phenomenon. The pier shapes surveyed in the sub-sample of 48 bridges include rectangular with rounded corners (21 bridges), rectangular (14 bridges), circular (10 bridges), square (2 bridges), and hexagonal (1 bridge). Fig. 5a shows that rectangular piers with rounded corners are the most affected by scour, with a within-sub-sample scour rate ( f c ) of 55.3% and accounting for 43.8% of the bridges affected by scour ( f s ). A substantial share of these bridges (39.5%) is associated with a non-zero flow attack angle ( ϑ ≠ 0), identified during inspections as a visible misalignment between the main flow direction and the pier longitudinal axis, highlighting that flow misalignment increases the scour vulnerability. Circular and rectangular piers exhibit comparable scour rates ( f c =47.6% and 46.7%, respectively), having a frequency equal to 20.8% and 29.2% of the scoured bridges, with similar incidences of ϑ ≠ 0. Hexagonal and square piers show lower impacts in terms of f s and ϑ ≠ 0, although these results are influenced by the limited number of observations. a b

Fig. 5. Frequency distribution of scoured bridges according to pier shape (a) and riverbed morphology (b), including within-sub-sample scour rate ( f c ), contribution to the scoured sub-sample ( f s ), and percentage of bridges with non-zero flow attack angle ( ϑ ≠0). a b

Fig. 6. Frequency distribution of the scoured sample according to the contraction factor (a) and the basin size (b): bridge percentage within the sub-sample ( f c ), within the scoured sub-sample ( f s ), and within the total sample ( f t ).

Fig. 5b shows that alluvial channels are the most prone to scour, with a within-sub-sample scour rate ( f c ) of 69.2%, contributing 56.3% of the scour-affected bridges and exhibiting the highest incidence of non-zero flow attack angles ( ϑ ≠ 0=59.0%) Embanked channels display moderate scour susceptibility, while incised channels show a lower