PSI - Issue 84

Giovanni Stasi et al. / Procedia Structural Integrity 84 (2026) 789–796

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1. Introduction The resilience of highway networks is vital (Rasulo et al., 2021), yet many mid-20th-century viaducts remain highly vulnerable to seismic events due to outdated design principles (Li et al., 2026). While modern retrofitting has shifted toward seismic isolation and energy dissipation (Capacci et al., 2020), applying these strategies to flexible structures with long natural periods presents significant technical challenges (Dolati et al., 2021). This study addresses this gap by providing a rigorous comparative analysis between distributed Lead Rubber Bearing systems and localized fluid viscous dissipation on a historical 1950s viaduct. By examining the selection of spectrum-compatible records for long period structures and evaluating non-linear dynamic responses under multi-directional inputs, the research offers optimized retrofit insights for highly flexible infrastructure. 2. Bridge description The highway bridge, built between 1958 and 1959 and opened to traffic in 1960, crosses a valley near Barberino del Mugello. The structure consists of two decks, each approximately 12.0 m wide, separated by an unequipped longitudinal joint. The decks are made of prestressed reinforced concrete with sliding cables. The overall length of the structure is approximately 290 m and consists of a series of seven single-support spans.

Fig. 1. Lateral view.

The first six are approximately 44 m long, with a 42 m spacing between the supports; the abutment beam between pier no. 6 and the Florence-facing abutment is 26 m long, with a 24 m spacing between the supports. The original deck has a cross-section consisting of 2 box girders with gross dimensions of 3.15m x 1.95m placed at approximately 6.20m, connected above by a 20cm thick slab, 2 support crosspieces with a thickness of 25cm and 3 and 6 intermediate crosspieces, with a thickness of 20cm, respectively for the 24m and 42m span beams.

Fig. 2. Deck plant and longitudinal section (original drawings)

The piers have a frame-type structure connected at the top by a reinforced concrete ribbed slab approximately 25cm thick and six 20cm thick ribs parallel to the longitudinal axis of the viaduct, with an overall height of 0.90m. The piers are 20.8, 30.0, 42.0, 42.9, 40.8, and 12.9 meters high from left to right. The abutments consist of ribbed walls with