PSI - Issue 78

Carmine Lupo et al. / Procedia Structural Integrity 78 (2026) 185–192

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which combine elastomeric flexibility with energy dissipation through the plastic deformation of the lead core. The devices are selected considering the seismic demand and the vertical loads.

Fig. 2. Geometric configuration of the analysed viaduct.

3.2. Fragility Analysis Fragility functions are useful tools for assessing the seismic vulnerability of highway bridges, supporting decisions regarding retrofit techniques, pre-earthquake planning and post-earthquake loss estimation. Fragility functions define the conditional probability of reaching or exceeding a specified damage state for a given set of inputs with variable intensity. The analytical approach allows for the characterization of structural response data by selecting appropriate Intensity Measure (IM) levels and defining the number of simulations to be performed at each level. These functions can be developed using data obtained from the seismic response of bridges from Non-Linear Time History Analysis (NLTHA). In this study, the Probabilistic Seismic Demand Model (PSDM) is used to derive analytic fragility based on nonlinear analysis. The PSDM is developed using a suite of 100 real accelerograms recorded from past earthquakes with magnitudes ranging from 5.0 to 9.0. The seismic input includes both near-fault and far-field ground motions, to account for the influence of epicentre distance on structural response. In this study, a preliminary analysis was conducted to evaluate the effect of different IMs, namely: Magnitude, Arias Index, Peak Ground Acceleration (PGA), and a fourth parameter, derived from the Sabetta - Pugliese velocity attenuation function, hereinafter referred to as Sabetta V. This parameter captures the effect of epicentral distance in seismic events with same magnitude. To this end, only the component of the Sabetta–Pugliese function that relates magnitude and epicentral distance was retained (equation 1), where: represents the moment magnitude and the epicentral distance (km); see Sabetta and Pugliese (1987). = [0.455 −log(√ 2 +3.62)] (1) The fragility analyses were conducted by considering several Engineering Demand Parameters (EDPs), selected according to the most critical failure mechanisms identified for the analysed bridge, and supported by previous research findings (see Petti and Mammone, 2019). Specifically, the considered parameters (EDPs) are the maximum relative displacement of the supports, the maximum relative displacement between adjacent spans (to account for hammering effects), the maximum shear force in the piers, the maximum absolute displacement of the bearing seat (pulvinus) and the maximum plastic hinge rotation at the base of the piers. Additionally, the cases of long and short piers were analysed separately. The thresholds were established in compliance with national standards. To investigate the structural behaviour of the system, three FEM models were developed using SAP2000 software. The models were nearly identical, differing only in the modelling approach used for the three bearing types. In