PSI - Issue 84

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

537

review under responsibility of the scientific committee of the Conference Keywords: Bridge vulnerability; Bridge piers; Piers-flow interaction; Bridge inspections; Scour; Hydraulic risk assessment

1. Introduction Bridges piers are fundamental structural components whose stability can be critically compromised by erosion processes acting around foundations. The removal of supporting sediments through hydraulic excavation, commonly known as bridge scour, represents one of the major causes of bridge failure worldwide (Arneson et al., 2012; Melville and Coleman, 2000; Neill, 1973). Scour develops from the interaction between hydraulic forces such as velocity and turbulence, and structural or geotechnical vulnerabilities including foundation type, pier geometry and soil characteristics. This framework is consistent with the classification provided in Arneson et al. (2012), distinguishing local, contraction and long-term scour and highlighting the influence of flow alignment, channel narrowing and sediment mobility on scour development. Many existing bridges were designed without fully accounting for hydraulic complexity or the influence of pier geometry on flow patterns (Brath and Montanari, 2000). Moreover, the frequent absence of a complete original design documentation increases uncertainties related to non-inspectable foundation elements, as results from several studies based on data collected during inspections carried out on existing bridges (D’Amato et al., 2024; D’Amato et al, 2025; Lo Monaco et al, 2024). These issues are explicitly addressed in the multi-level and multi-risk methodology introduced in the Italian Guidelines for bridge safety assessment (MIT, 2020). Extensive international studies confirm that scour is a dominant cause of bridge damage and collapse. In the United States investigations conducted by the Federal Highway Administration (FHWA) and the U.S. Geological Survey (USGS) led to the development of a national database including approximately 500 measured scour depths, demonstrating that hydraulic erosion during flood events is the leading cause of bridge failure (FHWA, 1998). Wardhana and Hadipriono (2003), analyzing nearly 500 bridge failures between 1989 and 2000, reported that hydraulic phenomena accounted for more than 50% of the collapses, a result later confirmed by Imhof (2004). Similar trends were identified in Italy. Studies by Ballio et al. (1998), Fiorentino et al. (1999), and Tartaglia et al. (2002), identified erosion as a major driver of structural vulnerability. More recently, Biondini et al. (2022) reported 106 bridge failures attributable to hydraulic causes between 2000 and 2019, with a further increase during the 2020 2021 flood events. Collectively, these surveys clearly demonstrate that scour-induced vulnerability remains a critical and widely recognized issue for infrastructure management. Increasing evidences suggest that scour occurrence and magnitude are not governed solely by flow intensity but are strongly influenced by geometric and morpho-dynamic factors. HEC-18 (Arneson, 2012) identifies contraction effects and flow angle of attack as primary drivers of scour development, while controlled flume experiments (e.g. Oliveto and Marino, 2017) highlight the role of local riverbed in governing vortex structures and sediment removal around piers. Large-scale statistical studies, such as the one presented in Harasti et al. (2023), based on several hundred bridge inspections, further confirm that variables including contraction ratio, approach-flow angle, pier shape, channel morphology, sediment texture and drainage basin size are significant predictors of scour depth. In particular, misalignment between flow direction and pier axis, narrow or constricted channel sections, and non-streamlined pier geometries were consistently associated with deeper scour holes. Experimental and numerical research also demonstrates that pier geometry strongly affects scour mechanisms. Blunt pier shapes intensify downflow and horseshoe vortices, whereas streamlined geometries, such as elliptical or lenticular sections, can significantly mitigate scour development (Vijayasree et al., 2019; Jalal and Hassan, 2020). Within this context, this paper focuses on a typological classification of existing bridge piers interacting with river flow considering a stock of bridges serving the Matera Province network (Basilicata, Southern Italy). In detail, based on data collected during 247 in-situ inspections, in this study preliminary results obtained by examining piers of 95 bridges having a Hydraulic Hazard Class varying from High (H) to Medium-Low (ML) are shown, among which 48 bridges of these are affected by scour. To this scope, a database is compiled, reporting material, geometrical and typological characteristics of piers with the main hydraulic attributes of the corresponding river courses, such as