PSI - Issue 62

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

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4

< 1945, 1945-1980 , > 1980, depending on period of construction or latest significant maintenance Class A, B , C, depending on design loads and span length ≤ 10,000 (L) , 10,001-24,999 (M), ≥ 25,000 (H) veh/day

Speed of deterioration

3

Design code

3 3 3 2 3 2

Exposure

Average Daily Traffic Average span length

≤ 20 (L), 20-50 (M) , >50 m (H)

Yes , No

Alternative routes Obstacle crossed

L, M , H depending on consequences

Transport of dangerous goods Yes, No Note: in bold values used for Bridge I , in underlined entries used for Bridge II.

It is worth mentioning that the level of deterioration is based on an element-level damage survey, in which each defect type has its own listed severity ( G = 1, 2, 3, 4, 5), and is assigned an extent and intensity by the inspector. From such detailed information, a level of deterioration can be computed for each element, then for each structural group (e.g., decks, piers, abutments, bearings, etc.), and ultimately for the whole structure. The level of deterioration of the whole structure is the worst level among the structural groups, whereas some averaging is allowed when assigning the level of deterioration of a structural group, as long as there are no elements with levels MH or H. A level of deterioration H means severe defects ( G = 4 or 5) on critical elements, i.e., conditions for which the structural safety is at stake; a level of deterioration MH means severe defects ( G = 4 or 5) with high intensity on non-critical elements, but which could compromise the structural safety over time. For full details, the reader is referred to Ministero delle infrastrutture e dei trasporti (2022) and ANSFISA (2022). Some relevant implications of the procedure are reported here: • For bridges with no restrictions, the hazard class is either MH or H, depending on the HGV flow. • When the level of deterioration is H, then the vulnerability class is H regardless of the other parameters; however, a vulnerability class H does not imply a level of deterioration H: in fact, a bridge with level of deterioration M or MH can have a vulnerability class H, depending on the other parameters reported in Tab. 1. • When the vulnerability class is H, the structural CA is H regardless of the hazard and exposure classes; however, a structural CA H does not imply a vulnerability class H: in fact, a bridge with vulnerability class MH can have a structural CA H if either the hazard or the exposure class is H. Finally, it is worth noting that prioritisation within the same class is not possible, as is the case for all qualitative methodologies (Chase et al., 2016). 2.2. Methodology proposed in the UK guidelines The risk-based methodology underlying the UK guidelines is set out in CS 451 (Highways England, 2020). This document closely follows CS 450 about inspections (Highways England, 2021). The Structural Review process determines the need for assessment of bridges and viaducts, although not all structures are considered in scope of the guidance. For example, single-span bridges or culverts with less than 1.8 m spans are out of scope. In addition, recent structures designed to support current loading requirement can be considered out of scope, as would structures that pose a low risk of failure due to current in-use loading, although this latter provision may be difficult to determine in practice. Subsequently, a Structural Review is undertaken for in scope structures prior to progressing any form of numerical assessment. Reference to previous inspection information is crucial and a lot of work has been undertaken in the UK to reduce subjectivity in the inspection process. This includes standardizing inspector competency, as well as the mechanism for determining extent and severity of specific defects, as well as the significance of the defective structural element. This is very much targeting the inspector’s knowledge of structural behaviour as a key characteristic of competency. There are a number of methods of standardising the bridge inspection process. One such method is the Bridge Condition Indicator (BCI) adopted by many Local Authorities (Sandberg et al., 2022). BCI indexing supports cross portfolio benchmarking with two key indices: the critical BCI, BCI crit , and the average BCI, BCI av . BCI crit provides valuable condition scoring on critical elements; this would be a suitable index for structural review purposes. BCI av