PSI - Issue 84

L. Fieno et al. / Procedia Structural Integrity 84 (2026) 1127–1135

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focus on safety, along with the need to monitor and assess the effects of deterioration on load-bearing capacity, made it possible to identify structural deficiencies worthy of further investigation. In particular, the full implementation of the Italian guidelines for bridge risk management ( Linee Guida per la classificazione e gestione del rischio dei ponti) has enabled managing authorities—primarily ANAS, as well as provincial and local bodies—to access the necessary funding for carrying out inspections and safety assessments. Moreover, these structures are often subject to architectural heritage protection constraints, which necessitate designing minimally invasive interventions that are compatible with structural requirements and consistent with the principles of conservation and preservation of architectural heritage. This report describes several experiences gained by the authors over the past two years on reinforced concrete arch bridges corresponding to the typologies described above. The activities carried out allowed for the precise identification of recurring defects and the main critical issues of these structures, as well as the direct verification of the challenges associated with bringing them up to current safety standards. 2. Case studies - Upper-deck arch bridge (Maillart type) The typical layout of this type of structure consists of two approach viaducts built with grillage decks monolithically connected to the piers, usually multi-shaft piers, with relatively short spans, generally not exceeding 20.0 m, and a central section supported by the arch. The main critical issues of this structural typology—leaving aside the complications related to construction methods, which have in fact led to its almost complete abandonment—are associated with the slenderness of the piers and the extreme structural irregularity. These characteristics make seismic retrofit to modern safety standards particularly complex and, in some cases, economically unsustainable. In some cases, later retrofit interventions, although intended to solve certain deficiencies, have introduced other, even more significant, critical issues. An example of this condition is represented by the present highway viaduct. The first image refers to the original design; the second shows the modified structural scheme following interventions carried out in the 1990s. The apparently limited modifications consist of the removal of the Gerber hinge support at Pier 4 (ex Pier 3) and a modification of the bearing configuration at the arch crown. The deck was strengthened in bending along all girders, and local jacketing was applied along the shafts and at the bases of the taller piers.

Figure 1: Longitudinal profiles of the viaduct in the original configuration and after the 1990s interventions;