PSI - Issue 84

L. Fieno et al. / Procedia Structural Integrity 84 (2026) 1136–1143

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1. Introduction and Standards The safety of existing bridges represents one of the major critical issues in the management of infrastructure networks, particularly in contexts characterized by structures that are often aging, designed according to outdated standards, and subject to progressive deterioration over time. In this context, the main reference standards are the “Guidelines for the classification and management of risk, safety assessment, and monitoring of existing bridges” and the “Operational instructions for the application of the Guidelines for the classification and management of risk, safety assessment, and monitoring of existing bridges – July 2022” . These documents are part of the national standards defined by Ministerial Decree of 17 January 2018 ( Technical Standards for Construction, NTC 2018 ) and the related Application Circular No. 7/2019. Specifically, by introducing a procedure based on successive levels of detail, the Guidelines provide an integrated framework for risk classification, safety assessment, and bridge monitoring, within which special inspections represent an advanced-level investigative tool, essential for acquiring additional information beyond that obtainable through routine surveillance. The Inspections are carried out in compliance with the minimum frequency prescribed in Section 7.4.1 of the Guidelines; with regard to scheduling, special inspections are required to be carried out no later than 5 years after the previous inspection for structures with Low and Medium–Low Attention Classes, and within 2 years for all other classes. In this paper, the topic of special inspections is addressed starting from the outcomes of the investigation campaigns carried out by the Authors in 2025 on approximately 100 structures within the ordinary road and motorway networks, through the presentation of selected case studies of particular interest that required detailed analyses and, in some cases, the adoption of targeted management measures. 2. Purpose of Special lnspections The primary objective of special inspections is to acquire information that supports a deeper understanding of degradation phenomena and of the structural condition of the asset, particularly when routine inspections have identified evident critical issues, or when exceptional events such as significant accidents, impacts, earthquakes, floods, or landslides may have affected the stability of the structure. In general, special inspections are also warranted when the study of predictive models highlights anomalous degradation behaviors, potentially in combination with periodic or continuous monitoring system. Special inspections are distinguished from routine inspections for the following main reasons: • They are carried out at close range, allowing accurate observation of identified critical issues; for this reason, they are considered “direct-contact inspections”. • They are accompanied by a material investigation campaign, focused primarily on “defects highlighted during routine inspections, with the aim of determining their origin, condition, and evolutionary trends.” • The operational mode of special inspections allows the detection of potential anomalies that may have caused degradation phenomena (e.g., improper drainage management with high chloride levels, inefficiency of vertical downpipes, deterioration or malfunctioning of joints, etc.). In line with the multi-level approach outlined in the 2020 Guidelines, the objectives of special inspections are as follows: • To deepen and document the understanding of degradation in the various parts of the structure through targeted testing, estimating the progression and evolution of degradation in a more deterministic and less qualitative manner, particularly by comparing current tests with any available past data . • To identify the causes and factors responsible for the observed degradation. • To update or confirm the Attention Class assigned to the structure and define the subsequent necessary actions, including the potential need to carry out a detailed safety assessment (VAL 4). 3. Structural Systems Investigated The structures under review include a wide range of structural types and static schemes commonly found in the national infrastructure network. The inspections specifically addressed bridges, viaducts, and overpasses made of