PSI - Issue 78

Samuele Faini et al. / Procedia Structural Integrity 78 (2026) 718–725

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Fig. 3. NLTH analyses on the “as - built” bridge: (a) horizontal design spectrum and selected (compatible) ground motion records; (b) shear -failure (t=2.95s) of mid-span columns; (b) horizontal (dir. X and Y) displacement time-histories at deck mid-span. 4. Overview of proposed seismic-retrofit intervention An overview of the proposed seismic-retrofit intervention is shown in Fig. 4-a. In the less critical longitudinal direction (i.e., dir. X), this accomplish a scheme enrolled in modern long-span r.c. arch bridges [Savor et al., 2008]: • low- friction (μ < 1 %) unidirectional bearings are used to disconnect the deck from piers no. 1, 2, and 7 (Fig. 1-a); • the same bearings are also installed at the abutment seats where longitudinal seismic displacements are reduced through hysteretic steel dampers [Wang et al., 2025]; • shock-transmit units (STUs) are applied at half and mid-span joints to inhibit relative (both longitudinal and transverse) displacements. Under service conditions, these devices are on the contrary designed to allow thermal expansions with negligible resistance. In the transversal direction (i.e., dir. Y), the proposed retrofit solution provides: • the use of four low-mass ( < 2.0% ) tuned mass dampers (TMDs), two units on each side of the central thermal joint (see Fig. 4-a), to mitigate transverse seismic accelerations. To avoid the application of additional loads to the girders, TMD s’ masses are supported by low-friction sliding guides anchored to the arch extrados, while spring and dashpot devices are connected to the above deck. The authors verified that additional TMDs’ masses (see next Section for design values) do not compromise the arch’s flexural and shear capacity at both ULS and SLS; • the shear capacity ( V rd ) of the short spandrel columns is enhanced using fiber-reinforced polymer (FRP) strips; • to regularize the asymmetric lateral response of the deck, cross-bracings are introduced between the long piers below half-joints. This allowed to achieve a more regular transversal mode shape (see Fig. 4-b).

Fig. 4. Retrofit intervention: (a) layout overview; (b) fundamental mode shape calculated in the transversal direction ( f=2.09Hz ).