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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bridge statics. In addition, the bridge deck examined is curved in plan in some road section, with very small supports with respect to the beams sections width. Therefore, a High S-CoA was obtained. It should be noted that the interaction between piers base and river flow in this case was significant (Fig. 4a and Fig. 4b). According to Italian Guidelines (MIT, 2020) it may increase over time both structural-foundational and seismic defect level at columns end sections, that are critical elements not only for S-CoA, but also for SF-CoA if foundation scouring occurs. Consequently, also the vulnerability of S-CoA and SF-CoA may result over time increased.

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b

Fig. 4. Viaduct I: (a) piers damaged by collision, (b) sediment abrasion or impact with boulders.

Frequently, amplified local scour phenomena are produced by a non-zero flow incidence angle (Oliveto et al., 2004). This situation is more frequent in pseudo-meandering rivers, where alternate bars are responsive to the stream direction and incidence angle changes near the piers or abutments (Fig. 5a). In the case of Viaduct II, the pier near the left bank was interested by local scour phenomenon due to the combined effects of non-zero incidence angle of main and lateral flow confluence. Therefore, for Viaduct II it results a Medium-Low hazard class for general scouring ( C a = 10-15%), and a High hazard class for local scouring (IEL > 1.2). Despite the presence of a weir downstream, the vulnerability related to local scouring was Medium-High and Medium for general scouring, and the H-CoA for general and local scouring was, respectively, Medium and Medium-High. a b

Fig. 5. Viaduct II: (a) Presence of alternate bars along the upstream channel; (b) interaction between pier, main and later flow confluence.

Viaduct II also recorded no significant defects on piers and abutments base. The bridge's defectiveness for SF-CoA was Medium, while the SF vulnerability was increased to Medium-High for parameters depending on the age of the last significant intervention done, the design standard, the bridge static scheme and materials. Similarly to the Viaduct I, the Viaduct II reported a High S-CoA for reasons linked to the absence of seismic restraints at deck supports. 3.2. Drainage flows and atmospheric agent interactions A relevant issue, often not adequately evaluated, is related to the increasing erosion risk due to the inadequate stormwater management system. In two bridges analyzed it was observed that the canalization system was damaged, producing local scouring around piers and abutments. As for the Viaduct III, the stormwater canalization failure induced a deep riverbed incision (Fig. 6a) directing stormwater runoff toward one pier (Fig. 7a). In the case of Viaduct IV, a deep riverbed incision directed close to the pier (Fig. 6b) induced a scouring condition and damage on the right abutment (Fig. 7b and Fig. 7c).