PSI - Issue 84

Antonella Cosentino et al. / Procedia Structural Integrity 84 (2026) 882–889

883

Keywords: Multilevel approach; ministerial guidelines; maintenance interventions; traffic models; Gerber saddles.

1. Introduction The application of the " Guidelines for the classification and management of risk, safety assessment and monitoring of existing bridges " on structures of the Italian infrastructural asset has highlighted a series of critical issues, outlining new and complex challenges for the management of a vast infrastructural heritage, extremely varied in terms of construction types and periods, and subjected to multiple risks. While on one hand the Guidelines offer a scientific and unified method for the management of existing bridges, defining timing and methods of intervention, on the other hand their practical application has highlighted a misalignment between the requirements of the standard and the real administrative capacity, especially of local authorities, which is notoriously conditioned by a lack of human and financial resources and by budget constraints that are inflexible compared to the complexity of the programming, design, and execution phases of complex works such as road bridges ones. The Province of Pisa has followed a virtuous path in the management of its approximately 340 bridges for years, also thanks to the promotion of research activities in collaboration with the Department of Civil and Industrial Engineering of the University of Pisa, having invested in census activities, visual inspections, and risk classification even before the promulgation of the Guidelines. The provincial bridges are constantly inspected, and the structural and foundational class of attention is known for each of them; the definition of the class of attention related to other risk sources is currently underway, specifying that at the moment the overall class of attention evaluation is available for 79 bridges, equal to 13% of the total bridges extent. Based on the class of attention, the Province then adopted a series of measures, such as the execution of Level 4 safety assessments, the imposition of road use limitations, and the design and execution of extraordinary maintenance interventions. One of the bridges particularly analyzed by the Province was the bridge over the River Arno, located along the provincial road SP 1 "della Botte". Since 2020, this has been subject of a specific research activity conducted in collaboration with the Department of the University of Pisa, which included the application of safety assessment approaches provided by Chapter 6 of the Guidelines, as well as further studies for the in-depth analysis of relevant topics, such as the development of traffic models based on real data acquired with Weigh in Motion systems. Once the main vulnerabilities and the residual capacity of the structural elements were known, starting from January 2023, a weight limit of 7.5 tons was imposed on the bridge; it was initially managed only with vertical signage to signal the limitation and the alternative routes for heavy vehicles; subsequently, because of frequent non-compliance with the imposed bans, physical gates were installed. In the meanwhile, the design of the extraordinary maintenance interventions was started. The process of design, verification, project approval, and award of works required a period of about 1.5 years, and it was possible to start the works only from mid-June 2024. Against a predicted duration of 9 months, it was possible to conclude the works only in October 2025. In addition to the redevelopment works, the installation of a continuous monitoring system was also planned to control the correct structural functioning over time. In the following paragraphs, a brief description of the research activities carried out on the bridge and their main results is reported; then the extraordinary maintenance interventions performed are illustrated, highlighting their technical peculiarities and the critical aspects from both the executive and management points of view. Indeed, the bridge is located in a highly anthropized social context, on one of the main road arteries of the Province, so in the execution of the interventions, an effort was made to never lose sight of social needs to minimize the discomfort caused by the interference of the construction site with local communities, while maintaining technical functionality as an essential and non-negotiable parameter. 2. The case study: “La Botte” bridge “La Botte” bridge crosses the Arno river and connects the territory of the municipalities of Calcinaia and Vicopisano. It is a bridge realized with three trestles connected by suspended spans using Gerber-type supports. Transversely, the three longitudinal beams of the deck are connected by crossbeams and a slab. All elements, both of the superstructure and the substructure, are entirely in ordinary reinforced concrete. The photo in Fig. 1 shows the structure of the bridge prior to the intervention. The geometric scheme of the plan and longitudinal profile is shown