PSI - Issue 84

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

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complete closure conditions, during which the dismantling of the existing suspended beams and their replacement with the new orthotropic plate decks was planned, after plating the Gerber saddles. The preliminary consolidation of the trestles and the slab, in addition to ensuring the capacity required for the structure at the end of the intervention, was necessary in the execution phase to safely conduct the dismantling and the placements operations of the suspended beams. The project planned for the underside work to be conducted with suspended scaffolding set up in phases to respect the prescriptions dictated by the Tuscany Region, which has jurisdiction over hydraulic matters. Particularly complex from an operational point of view and time-consuming was the reinforcement of the reinforced concrete structural elements through the removal of damaged concrete, passivation of existing reinforcement, insertion of additional reinforcement, and shotcrete thickening (Fig. 6), because of the particular geometric shape of the trestles. Indeed, the reinforcement involved overhead works, which by the Contractor's choice was performed using a "by-bridge" vehicle instead of the suspended scaffolding provided by the project; similarly, the reinforcement of the existing Gerber saddles - through the insertion of a new connecting crossbeam and the reinforcment of the saddles with steel structural plates (Fig. 6) - proved to be a long and difficult operation considering their final position beneath the existing slab.

Fig. 6. Supplementary reinforcement for longitudinal beam thickening and plating of Gerber saddles

The need not to increase the permanent loads on the structure, which led to project solutions with very low thickness for the paving, triggered further critical elements such as, in addition to the creation of the resin paving itself, the use of expansion joints made specifically for the structure. Besides the technical aspects listed above, the time delay certainly also depended on the construction site methods; in fact, to minimize road traffic discomfort as much as possible, the phases of complete traffic closure on the bridge, although increased compared to project predictions, were limited only to the phases of replacing the suspended beams, while most of the work was performed under one way traffic conditions, reducing productivity and requiring greater care for worker safety. It should be emphasized that similar construction sites with non-standardizable works would require a very serious and articulated programming approach, which proved very difficult for the economic operator to apply. Despite the constant presence of workers on construction site, who also operated during holidays in particular phases of the work, the difficulties determined by the timing of supply of steel elements and, above all, their installation - as well as the thickening of the trestles (perhaps not adequately estimated in the design phase) - resulted in execution times that were not fully compliant with expectations. In this scenario, it should not be overlooked that during the execution of the works, the territory of the Province of Pisa was hit by 4 events for which a state of emergency was recognized (September 23, October 18 and 26, 2024, and March 14-15, 2025), including a high alert event for the flood of the Arno river. Upon conclusion of the works, due to the aforementioned causes, the total cost of the intervention further increased to € 4250000.00.