PSI - Issue 64

Nicoletta Bianchini et al. / Procedia Structural Integrity 64 (2024) 352–359 Bianchini N., Sabra Z, Green K.. Wrigth, R. Structural Integrity Procedia 00 (2024) 000 – 000

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1. Introduction Numerous historic masonry arch bridges across Europe and the United Kingdom continue to function despite exhibiting structural deficiencies. In the United Kingdom, over 70,000 masonry arch spans have undergone design modifications and load adjustments, often involving the incorporation of new materials and bearing elements, with adherence to modern standards being uncommon. This situation results in a limited understanding of these structures, affecting the precision of bridge capacity assessments, especially given practical constraints such as time, costs, client requirements, traffic restrictions, hardware and software resources. This study emphasises the practitioner's perspective, acknowledging the challenges they face in adhering to strict deadlines, rigorous standards, and regulations — both structural and non-structural. It underscores the need for efficient methods that balance cost considerations and align with realistic scenario limitations inherent to the in-situ specificity of the work. A typical case study of a composite bridge consisting of two spans with restricted accessibility in Waverley Abbey, Surrey is used to deepen the discussion. Two main aspects are investigated: the risk of flooding which is constantly increasing due to climate change; the diagnostic phase, which employs materials investigations, in-situ non destructive like Ground Penetrating Radar (GPR) and more intrusive techniques such as coring; and in the second part of the study, a numerical assessment limit state analysis for various loading scenarios and flooding conditions. 1.1. Flooding in literature In the last few decades, various masonry arch bridges in the UK have incurred failure or serious damage due to extreme flood events, as listed by Maytan et al. (2022). Flooding is effectively the increase in a river’s normal stage height, resulting in a faster water flow that poses increased loading on bridges located in the path of water surges (Hamill 1999).When assessing masonry bridges under loading conditions resulting from environmental conditions, the lack of available information (e.g. geometry, hidden elements) causes high level of uncertainties due to the assumptions required while representing the environmental actions and the parameters of the materials (Jonkman 2014) (Moreira, et al. 2016). In general, fluvial flooding generates both hydrostatic and hydrodynamic effects; Quantification of the hydrodynamics forces on the bridge superstructure are not yet comprehensively understood, however they have the potential to cause structural failure. This is because buoyancy effects reduce the gravitational effects of the masonry and the backfill (Hulet, Smith and Gilbert 2006). Nevertheless, only American standards give information on how to deal with flooding effects (2004) and few experimental studies have been carried out at this stage (Proske, et al. 2018). Conversely, scour actions and debris impact are widely studied and ruled (CD 356 “Design of highway structures for hydraulic action” , CS 469, formerly BD97/12 “The Assessment of Scour and Other Hydraulic Actions at Highway Structures” , and CIRIA C742 “Manual on scour at bridges and other hydraulic structures” , CS 470 “Management of sub - standard highway structures” , US NCHRP Report 445 2” Debris forces on highway bridges” ). Since it is challenging to obtain the force-time histories of flooding events, numerical modelling could overcome this limitation by means of computational fluid dynamics which can be coupled with the FEM model of the structure, such as: finite difference method (FDM) (Huang and Xiao 2009), and the finite volume method (FVM) (Chu, et al. 2016) by applying a volume-of-fluid (VOF), smoothed particle hydrodynamics SPH model coupled with both FEM and DEM (Hasanpour, Istrati and Buckle 2021, Capasso, et al. 2022). Those approaches are precise and satisfying, especially for research, learning and development purposes, but highly demanding in terms of computational effort, time and costs, often making them impractical for routine use. Fast, replicable and reliable results can be obtained by adopting limit analysis with the proper considerations due to flooding. This paper validates some common practical assumptions about flooding effects by means of limit analysis on the case study of Waverley Mill Bridge after a wide investigation and diagnosis stage. 2. "Case study: Waverley Mill bridge" The Waverley Mill bridge carries Waverly Lane (B3001), a single carriageway over a non-navigable stretch of the River Wey. The date of construction is estimated to be around mid- 1800’s . Positioned near the town of Farnham