PSI - Issue 84

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

886

evaluated, adopting load restriction measures for the period necessary for the design and implementation of interventions, set by the Guidelines at a maximum of t ref = 5 years. The bridge could be crossed by vehicles with a maximum mass of 7.5 tons. Research insights into traffic models On the road served by the bridge, in the period preceding the imposition of weight limits, Weigh in Motion (WIM) systems were installed for traffic data collection and subsequent processing. The WIM systems consisted of quartz sensors and inductive loops embedded in the asphalt, placed on both lanes,. They allowed the recording of more than 1500000 vehicle passages with their main characteristics: time of passage, lane crossed, total weight, length, speed, number of axles, and weight of individual axles. The same activity was carried out on two other roads managed by the Province of Pisa, also of interest due to the presence of strategic structures and high values of average daily traffic; similar WIM systems were installed on these. The processing of data collected by the three WIM systems provided statistics on traffic composition, and allowed the probabilistic definition of traffic models to evaluate the actual demand imposed on the structural elements of the bridges. The results provided by the University of Pisa highlighted two fundamental aspects: • a high frequency of vehicles with a total mass exceeding 44 t (limit imposed by the Italian road regulation); • the possibility of reducing the verification loads, in particular the distributed load value especially for spans longer than 10 m. A verification model was therefore proposed, applicable to bridge structures in the provincial territory, as a function of the lengths of the constant-sign influence lines and considering the real vehicular flow; its distributed load can be estimated as: = 3⋅− 600 ≥ 2,5 2 ⁄ (1) where Q k is the point load provided by the load schemes of NTC 2018 and L tot is the total length of the bridge. 3. Extraordinary maintenance intervention The maintenance intervention had been planned by the Province in 2020, including it in the intervention plan financed with Ministerial funds assigned to the Province of Pisa with D.M. 123/2020 for a presumed cost of €1500000.00 for the 2021 financial year. Design activities started in September 2022; the external designers still deemed it necessary to perform a further investigation campaign, to examine geotechnical aspects and the substructures. This further campaign did not highlight particular criticalities for the substructures. In the meanwhile, in December 2022, the results of the safety verification were delivered, from which the weight limit described above arose. The cost of the intervention estimated during the design phase was €3750000.00, mainly due to the rise in material costs happened in May 2022. The design provided solutions such as the reinforcement of the slab and trestles through concrete and shotcrete with the insertion of additional reinforcement, the replacement of the suspended beams with new orthotropic plate decks, and the reinforcement of the Gerber saddles with metal plating, as visible in Fig. 4. The execution of the structural interventions was also an occasion for the creation of cycle-pedestrian paths, the insertion of new expansion joints, new furnishings, and new platform hydraulics. The project incorporated all the requirements provided, such as those related to hydrogeological and landscape constraints imposed by the consultation with the other involved subjects, which lasted from June 2023 to December 2023—well beyond the 90 days provided by Italian law, due to the delay in transmitting the opinion by the Superintendency, despite repeated reminders. The initial scheduling of the works sought to satisfy the needs of the involved local authorities and to minimize as much as possible the discomfort to the communities, reducing the predicted complete closure to traffic to only four months, necessary for the replacement of the four suspended beams. This deadline was extremely challenging as it required working on two suspended beams at a time. Furthermore, the choice of the Province of Pisa was to manage the Works Management internally, having qualified personnel available.