PSI - Issue 84

S. Lorefice et al. / Procedia Structural Integrity 84 (2026) 669 – 676

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7 Results of Analyses – Existing Bridges (Ante-Operam) Initially, modal analyses and linear elastic response spectrum analyses were conducted, followed by nonlinear static (pushover) analyses along the longitudinal and transverse directions of the bridges. Specific control points were selected to monitor the evolution of the structural response under orthogonal loading conditions. Two distinct collapse mechanisms were identified. In the longitudinal direction, the collapse mechanism involves four plastic hinges alternating between intrados and extrados of the first arch. In the transverse direction, inelastic phenomena are concentrated at the base of the piers, corresponding to a flexural failure mechanism. Figures 7 and 8 illustrate the damage patterns and major deformations of piers, arches, and backfills at the load step conventionally associated with the Life Safety Limit State (SLV). These observations apply to both existing bridges.

a)

b)

Fig.7.Example of pushover results for (a) longitudinal and (b) transverse loading – six-span bridge, ante-operam

c)

d)

Fig.8.Example of pushover results for (c) longitudinal and (d) transverse loading – three-span bridge, ante-operam

8 Consolidation of Existing Bridges Based on the ante-operam analyses and observed deficiencies, a series of structural strengthening interventions were proposed to increase the safety level while preserving the architectural appearance and structural concept of the bridges. The consolidation strategy for the arch barrel depends on the material: • Masonry structures: grouting with cementitious or lime-based mixes combined with reinforced plaster applied on both intrados and extrados. • Concrete structures: reinforcement solely with reinforced plaster. The latter is specifically intended to mitigate cracking observed in the ante-operam analyses. In the 3D FEM models, the planned consolidation interventions were incorporated. The effectiveness of masonry grouting was modelled by increasing the mechanical properties of the masonry by a factor of 1.2, in accordance with Table C8.5.II of Circular 7/2019 (NTC18). The reinforced plaster (welded wire mesh Ø12/10 cm) was modelled using one-dimensional beam elements. To ensure mesh compatibility, the geometry of the reinforcement mesh was constrained to the pre-existing arch mesh, resulting in a modelling step of 25 cm. Equivalent diameters for beam elements were calculated to match the actual cross-sectional areas of the reinforcement bars.