PSI - Issue 84

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ScienceDirect

Procedia Structural Integrity 84 (2026) 1270–1277

© 2026 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the scientific committee of the Conference Keywords: bridge; hydraulics; hydrodynamic forces; low Froude number; wood debris. Abstract Understanding the hydraulic forces exerted on bridge decks is critical for assessing structural safety during flood events, especially at low Froude numbers ( Fr u < 0.6). This study provides preliminary insights into the complex interactions between flow and debris accumulations. To this end, isolated wood debris logs were tested in a hydraulic flume under various submergence levels. Results show that even at low Froude numbers, the presence of debris significantly alters the flow field, increasing both drag and uplift forces. Specifically, data analysis reveals that both horizontal and vertical components of the hydrodynamic loads depend on debris characteristics as well as backwater and difference in water levels across debris, suggesting that current hydraulic design practices may underestimate the forces acting on bridge superstructures under low-velocity and floating debris. This study offers useful design indications which are worth further analyses, including numerical, experimental and theoretical. 1. Introduction During flood events, rivers frequently transport large wood debris (LWD), which may accumulate at hydraulic structures such as bridges piers and/or decks. These accumulations reduce the effective flow cross-section and alter the momentum balance of the flow, thereby intensifying flood hazard and structural vulnerability (Naudascher and Medlarz 1983; Schmocker and Hager 2013; Schalko et al. 2019). The primary hydraulic consequence of debris accumulation is the backwater rise ( h bw ) upstream of the structure, while downstream levels remain comparatively lower, resulting in a difference (  H ) between upstream-downstream III Fabre Conference: Existing Bridges, Viaducts, and Tunnels: Research, Innovation, and Applications Hydraulic forces on debris accumulations: a preliminary analysis Stefano Pagliara a, *, Ajit Kumar a , Claudio Rossi a , Michele Palermo a a DESTEC – Department of Energy, Systems, Territory and Construction Engineering, University of Pisa, Via Gabba 22, Pisa, 56122, Italy

* Corresponding author. Tel.: +39 050 2217717. E-mail address: stefano.pagliara@unipi.it

2452-3216 © 2026 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the scientific committee of the Conference 10.1016/j.prostr.2026.06.162