PSI - Issue 62

Alessandro Lipari et al. / Procedia Structural Integrity 62 (2024) 24–31 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

25

2

1. Introduction Bridges are critical parts of a transport network and ensuring their safety is paramount while they are ageing. However, this has proven to be a challenging task: the bridge stock may be close to or have exceeded its expected lifespan, traffic loads have increased over the years, climate change imposes unpredicted actions, maintenance operations may be costly and typically causing undesired traffic disruptions, available resources are often tight (Clemente, 2020, Buffarini et al., 2022). Although monitoring systems have been used (Clemente et al., 2019, Bongiovanni et al., 2021), collection of data about bridge conditions is still greatly relying on visual inspections and, as such, their outcome has a certain degree of subjectivity. Therefore, not only is the subsequent bridge health assessment affected by subjectivity in its input data, but the methodology applied may differ among road managers, even within the same country, potentially leading to inconsistent outcomes. To tackle this, some countries have adopted national guidelines in an effort to minimise subjectivity and enhance uniformity in inspection and assessment tasks. Among these, the Italian Ministry of Infrastructure and Transport has recently issued the “Guidelines on risk classification and management, safety assessment, and monitoring of existing bridges” (Ministero delle infrastrutture e dei trasporti, 2022), whereas in the United Kingdom the Design Manual for Roads and Bridges includes more established procedures for the inspection and assessment of existing highway bridges (Highways England, 2021, Highways England, 2020, National Highways, 2022). Both guidelines are risk based and follow a comparable multi-level approach. The Italian guidelines comprise of six levels (0-5): census (L0), inspection (L1), definition of a Class of Attention (L2); then, according to the outcome of L2, an existing bridge may be required to proceed to a preliminary assessment (L3), an accurate assessment (L4), or a network resilience study (L5, applicable only to high importance bridges). The Italian guidelines endorse a multi-risk methodology, as they take into account four main risks: structural-foundational, seismic, landslide and hydraulic. Each of these risks is derived from a combination of hazard, vulnerability and exposure classes, resulting in a Class of Attention (CA). The combination of each risk CA’s leads to an overall CA, upon which depend further actions . The UK guidelines are based on a broader set of documents. The parts applicable to bridges can be broadly divided into inspection, structural review, and assessment. As such, these stages can be related to the Italian levels L1, L2, and L3-L4. Procedures for determining the structural and hydraulic risks are separated and do not lead to a unified multi-risk outcome. Note that the seismic risk is not included due to its scarce relevance across the UK territory, and landslide risk is not treated explicitly within the Design Manual of Road and Bridges. This paper focusses on the structural risk of highway bridges and compares the overall methodology and some specific procedures required to establish the need of a structural assessment, i.e. the Italian Level 2 and the UK structural review. Therefore, the outcome of the bridge inspection is already known, as well as any other data required as input. The outcome of the procedure is, for the Italian guidelines, a CA, and for the UK guidelines, a reliability and risk score; in both cases, the outcome affects the requirement for further actions, such as a structural assessment. The procedures are then applied to two case studies, and similarities and differences are highlighted. 2. Methodology The Italian and UK methodologies to estimate the structural risk of existing highway bridges are outlined in the following. The bridge condition level is a crucial input in the procedure, although not the only one. Consideration of multiple factors is indeed a remarkable feature of both methodologies. 2.1. Methodology proposed in the Italian guidelines The methodology underlying the Italian guidelines is multi-level, multi-risk and qualitative. It has to be applied by all road managers for bridges and viaducts longer than 6 m. Risk is always rated upon a combination of hazard, vulnerability and exposure, resulting in a CA, which can be Low (L), Medium-Low (ML), Medium (M), Medium-High (MH), or High (H). Solely for enabling a comparison with the UK methodology, it is assumed that the non-structural risks (seismic, landslide/hydraulic) will not affect the