PSI - Issue 44

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Agnese Natali et al./ Structural Integrity Procedia 00 (2022) 000–000

Agnese Natali et al. / Procedia Structural Integrity 44 (2023) 2012–2019 © 2022 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 XIX ANIDIS Conference, Seismic Engineering in Italy Keywords: Risk classification; Bridges visual inspections; Damage detection; Explainable Artificial Intelligence algorithm.

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1. Introduction The Italian “Guidelines for classification, risk management, assessment of level of safety and monitoring of the existing bridges” (Ministero delle infrastrutture e della mobilità sostenibili, 2020) provide a new smart method for the management of the existing bridges and viaducts. Indeed, the related severe collapses and strong damages happened in the last decade in Italian territory highlighted the need of an unified and easily-applicable approach to firstly have a comprehensible and comparable view of the status of all the infrastructures in the country, and secondly define a structured programme of activities for their management. In addition to the Guidelines, the Italian Superior Council has just approved a new document called “Istruzioni Operative” (from here on “Operating Instructions”) (Ansfisa, 2022), which is a commented version of the Guidelines, with practical information and strategies suggested for a clearer and guided application of the method proposed by the Guidelines. This method is new because: in Italy, there was no unique approach for this issue, before; although other methods can be found both in literature or among those in use by the road managers, called in general “Bridge Management System” (BMS), the philosophy and the structure are different. Indeed, for all these other existing methods, the final product is a numerical index which is representative in some cases of the degradation phenomena of the structure (CIAS - Censimento, Ispezioni visive, Tecniche di ripristino, Indagini sperimentali, 2011), while in other cases also comprehends the interaction of the conservation status with structural features, traffic flows, seismic and hydrological risks (ANAS, Direzione Operation e Coordinamento Territoriale, 2018; Franchetti et al., 2003; Montepara et al., n.d.). As a general assumption, gathering all these factors in a single index make not easy to understand which of them is relevant, hence complicating the consequent phases of planning the intervention priorities. Besides, it does not consider that the different risks, as structural, seismic and hydro-geological ones, depend on dissimilar sources and are related to events with different return periods. At the same time, the methods that consider the degradation phenomena only, lack of referring to other relevant risks (like hydro-geological ones), which proved to be among the most responsible for collapses of severe damages (Deng et al., 2016; Tan et al., 2020). Instead, the new method by the Guidelines is a qualitative approach for the evaluation of risk, which first considers separately all the different sources of risk – structural, seismic, geological and hydraulic – aiming at the evaluation of a “Warning Class” (WaC) for each one (the higher is the WaC, the more critical is the level of risks evaluated). Then, the global WaC is provided, which summarizes and considers the interaction among the different risks. In this way, even if a unique judgment is obtained, the influence of each considered parameter and the relevant risk for the final WaC are clear, and support the organization and prioritization of the following activities. The method introduced by the Italian Guidelines is smart because of its structure, which it perfectly fits the activities with their timing and costs, with the actual needs of each bridge. Indeed, the method is divided in two big macro-levels: from Level 0 to 2, the method is applied to all the structures; from the Level 3 to 5, it is applied to the structures which really need further analyses due to the structural, and/or seismic, and/or hydro-geological issues found from the previous levels of analysis. The deeper is the level of analysis, the more difficult, time and cost expensive are the connected actions, but, at the same time, the number of bridges which need of deeper analysis decreases. Hence, the method is structured by always balancing the action timing and complexity with the number of structures requesting for these actions. The core of the method, which divides the two macro-levels, is the Level 2, which foresees the evaluation of the previously announced “Warning Class”, for each risk and then the global one. Basing on the obtained WaC, the following activities, including the necessity of application of the further levels of analysis, are established and organized. The quality of the evaluation of the WaC is based on the information and data gathered in the previous levels, hence the good execution of these previous activities is fundamental to guarantee the success of the classification. In the following, a more detailed explanation of the activities foreseen from the Level 0 to the evaluation of the WaC is provided, highlighting that all these activities have to be executed for all the structures,