PSI - Issue 78

Andrea Nettis et al. / Procedia Structural Integrity 78 (2026) 1412–1419

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superstructure and substructure. In the longitudinal direction, piers are characterized by pinned supports, while sliding bearings are assigned to the abutments. No strength limits are imposed on the pinned supports. The superstructure consists of three V-shaped pre-stressed concrete girders. The primary geometric characteristics of the case-study bridges are illustrated in Figure 1. The configurations vary in terms of total length and vertical profile, including bridge layouts with two, four, or six spans., each span being 35 meters in length. Pier heights of 7 m, 14 m, and 21 m are used to represent both regular and irregular geometric configurations.

Fig. 1. Parametric case-study bridge realisations.

3.2. Modelling and fragility analysis assumptions Numerical models of the presented bridge realisations are carried out by using the Opensees framework (McKenna, 2011). The superstructure is modelled as an elastic frame and connection between the superstructure and substructure components is achieved using two-node link elements. Nonlinear behaviour is concentrated in the piers, which are modelled using ForceBeamColumn elements incorporating a fibre discretization of the cross-section. TThe analytical iterative computations required for the DBA procedure are implemented through custom programming routines developed in MATLAB. The force – displacement relationships assigned to the inelastic supports are derived from sectional moment – curvature analyses, in conjunction with estimates of the equivalent cantilever heights of the piers. The equivalent viscous damping ratio for each pier is estimated using the ductility-based formulation proposed by Priestley et al. (Priestley et al., 2007). To account for record-to-record variability in fragility analysis, a suite of 100 natural, unscaled ground motion records is employed, selected from the SIMBAD database (Smerzini et al., 2014). Each record is applied independently in both the transverse and longitudinal directions. For fragility analysis, given the system-level loss assessment, the seismic demand and fragility curves are expressed in terms of the SDoF displacement demand. Four displacement-based DS thresholds are calibrated consistently with the attainment of curvature limits at the pier base (Table 1). Corresponding damage-to-loss ratios (DLRs) are defined in Table 1. The calibrations of the DS thresholds are carried out while carrying out the displacement-based pseudo-pushover analyses and estimating the relationships between equivalent SDoF displacement demand and curvature at the pier base. The adopted IM is the . Hazard curves related to the city of L’Aquila (Italy) are used . Table 1. Damage state thresholds and damage-to-loss-ratios ( : concrete compression strain, and ℎ : the geometric percentage and yielding strength of transverse reinforcements, ′ : compression strength of the confined concrete, ε su : ultimate deformation of longitudinal steel bar). DS1 DS2 DS3 DS4 Pier curvature ( ) χ ( =0.004) χ( =0.004+ 1.4 ℎ ε su f c′ c ),0.6ε su ) χ DLR 0.03 0.08 0.25 1.00