PSI - Issue 62

Anna Rosa Tilocca et al. / Procedia Structural Integrity 62 (2024) 1043–1050 A.R. Tiloccai et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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fundamental to satisfy performances of infrastructures over their life span, taking into account costs, losses and alternatives recording inspections data and planning short/long term interventions (Pellegrino et al., 2011; Dinh et al., 2009; Sasmal et al., 2007; Rokneddin et al., 2013). Nevertheless, external factors like exposure and risk due for example to geotechnical or hydraulic aspects were rarely considered and also without uniform approach at national level. For this end, Italian government has decided to apply a new procedure analysis, based on a multilevel approach composed by five different levels in order to obtain an attention class index (CDA). The full name of this multilevel approach is “Guidelines on Risk Classification and Management, Safety Assessment and Monitoring of Existing Bridges” (CSLP Ministry of Infrastructure, 2020) and was issued mainly as a consequence of the collapse of “Polcevera” bridge (Morandi, Genova) in 2018 and the seismic events that occurred between 2016 and 2017 (Cal vi et al.,2019; Bazzucchi et al., 2018), considering that Italian Code and relative explicative upgrade (NTC, Ministry of Infrastructure, 2018-2019) are principally focused on existing structures like buildings without any considerations on existing bridges and their maintenance planning. Moreover, a last review occurred in 2022 integrates the “Operative Instructions” by ANSFISA (National Agency for the safety of railway, highway and roads infrastructures). The aim of the Italian Guideline is preventing inadequate damage levels making on fact acceptable the risk. It is composed by three different parts, starting to the initial risk classification and census, passing through the safety check until the last phase where monitoring and supervision are expected for the long-term analysis. Only bridge or viaduct with a span greater to 6 meters, which allow to overcome a depression in the ground or a hydraulic canal considering also communication route or a natural/artificial discontinuity, are considered in the multilevel approach. Furthermore, at the beginning of the analysis the different kinds of risk are taken into account from the Italian Guideline in a singular way, evaluating the attention class index for structural-foundation risk, seismic risk, hydraulic and geotechnical risks in terms of hazard, vulnerability and exposure. These risks, initially analyzed separately, are then brought together in a single general classification of the attention class (CDA). The objective of that work is the application of Italian Guideline on a railway bridge until the evaluation of the attention class index (focused on the first three levels 0-1-2), in order to increase the knowledge on this kind of bridges and analyze if and how the multi-level multi-risk approach allows to understand critical aspects of railway typologies structures or if particular suggestions are necessary. 2. Multi-level multi-risk approach The approach descripted by Italian Guideline for the evaluation of the general attention class index (CDA DEF ) is composed by six different levels with increasingly greater degrees of depth and complexity and here reassumed: • Level 0, provides indications for the census of all principal characteristics colleting available data, design documents and inspections results; • Level 1, provides indications for specific onsite visive inspections for knowing the real state of degradation and verify the presence of significant defects on structural and non-structural elements. Moreover, potential risk conditions associated to landslides or hydraulic actions are evaluated; • Level 2, provides indications about the estimation of the attention class indexes (CDA i ) for the bridge, after the information collected in level 0 and 1, based on parameters with qualitative risks (structural-foundation, seismic, geotechnic and hydraulic) taking into account hazard, vulnerability and exposure; • Level 3, involves the execution of preliminary assessments, in function of what is detected in the level 1 inspections, aimed at understanding if it is still necessary to proceed with in-depth investigations by carrying out accurate Level 4 checks; • Level 4, consists in the execution of accurate evaluation as reported in the Italian Code (NTC, 2018); • Level 5, additional level, for high importance bridges and taking into account the network resilience. In the present work the evaluation of the global attention class (CDA DEF ) is based on the analysis of the level 0, 1 and 2 for a railway bridge. 3. Level 0: census and description of railway bridge The bridge census expected from level 0 consists in a sort of cards for all structures that constitute the entire infrastructure, also relatively to the network site location, for catalog the principal geometrical and material characteristics. The information collected allow to subdivide the infrastructure in macro-class for program the onsite inspections. In our case, the railway bridge length is about 780 meters, composed of 23 spans realized by prestressed concrete rectangular section elements, each-one about 25-meter length (see Figure 1a and Figure 1b). A terminal portion of the viaduct (160m, 2 spans) bypass the presence of a highway (A1), and it is characterized by mixed structure steel-concrete (concrete slab infilled with HEB1000 beams and sustained by 3 series of 42 reinforced concrete pillars 5.5m high). This terminal part is excluded from the present work. Concerning to the vertical elements, the railway bridge is composed of 23 reinforced concrete columns with a variable high, ranging from 4.5m to 6.25m (see Figure 1c) and 2 reinforced concrete shoulders at the ends.