PSI - Issue 62

Sergio Ruggieri et al. / Procedia Structural Integrity 62 (2024) 129–136 Author name / Structural Integrity Procedia 00 (2022) 000 – 000

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Nomenclature AI

Artificial Intelligence Average Precision i th -class CNN Convolutional Neural Network DL Deep Learning FN False Negative mAP Mean Average Precision P Precision R Recall RC Reinforced concrete R-CNN Region - Convolutional Neural Network TN True Negative TP True Positive YOLO You Look Only Once AP i

1. Introduction The recent events involving the collapse of important existing bridges in Italy have mobilized the public institution to propose new strategies for ensuring the safety of the existing bridge portfolios and to provide a new concept for developing reliable risk mitigation plans. With this regard, the main actors involved in this process are the road management companies, which have the task to assess the health state of the existing bridge assets and to employ adequate strategies towards possible failures. The main measure that Italian government recently employed is the guidelines on the structural safety of existing bridges (MIT, 2021), released in 2021 and made mandatory for management companies. The approach proposed by the guidelines consists in a systematic multi-level approach, which in the next years should be applied on the entire national bridge stock and should allow to identify the units presenting the worst condition and, on those, to apply monitoring and maintenance strategies (do not excluding possible demolitions and reconstructions). The proposed approach consists in the application of six consecutive levels at increasing effort. The first three levels allow to perform a screening to establish, even if in a simplified way, the most critical cases, which should be object of further detailed investigations and actions. These latter are accounted in the second three levels, which guide the management companies to take some decisions on specific structures, such as structural interventions (e.g., retrofit, reconstruction) or service limitation (e.g., traffic reduction, limitations in terms of maximum weight of trucks). In the first phase of the application of the new Italian guidelines, management companies and the scientific community worked to implement the first three levels, which as above stated cover a crucial role in the risk assessment, considering that the main further actions depend on the obtained output. Let us focusing on the first three levels, in which levels 0, 1, and 2 have to be implemented. In particular, level 0 consists in the collection of documentation of each bridge constituting the managed road network, starting from the original drawings up to the retrofit and manutentions designs developed over the time. Besides structural information, comprehensive of structural characteristics, geometrical and mechanical parameters, and constructive details, other data should be collected, such as the contextual information related to environmental risks around the structures, including seismic, hydraulic, geotechnical, and geological sources of hazards. After this phase, level 1 consists in the periodical inspection of each bridge within the investigated road network, for which well-instructed surveyors detect the main defects characterizing the elements of bridges. Each structural element, such as desk and beams, pillars, supports, abutments, is accurately observed, in order to identify potential vulnerabilities and possible phenomena deriving from other environmental risks. On the base of the inspection, level 2 can be employed, in which through a logical path, a risk class is defined. This latter is obtained from the quantification of sub-risk classes associated to all considered hazards (i.e., structural, seismic, hydraulic, and geological). Five different risk levels are defined by the guidelines, that is, low, medium-low, medium, medium-high, and high. According to the risk quantification, the management companies can define the actions to perform on the structure. As for example, bridges reporting high risk should be assessed through the procedures at level 4, which provides the assessment to different limit-states (e.g.,