PSI - Issue 78

Stefano Bozza et al. / Procedia Structural Integrity 78 (2026) 1213–1220

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section of the piers were used for the pier shaft, while rigid elastic frames were instead used to model the pier cap. A fiber-based nonlinear hinge was placed at 1.0 m from the base, considering a 2.0 m hinge length. An elastic-plastic behavior was assigned to each steel fiber representing the rebars, and a kinematic hysteresis model was chosen. Moreover, Mander constitutive law and Takeda hysteresis were used to define the non-linear cyclic behavior of the concrete fibers. Each pier section was discretized into 92 steel fibers and 116 concrete fibers. The load bearings were modeled as linear elastic link elements, fixing the vertical degree of freedom, assigning a high stiffness to the restrained degrees of freedom (horizontal displacements) and using a very small stiffness along the free degrees of freedom (e. g. rotations); the free degrees of freedom are reported as arrow in Fig. 3. The shear keys were also modeled with linear elastic link elements, using a high stiffness along the restrained degree of freedom and negligible stiffness along other directions. Furthermore, since the bridge has deep foundations, soil-structure interaction was neglected, using fix restraints at the base of the piers. Abutments are very stiff elements rigidly connected to the ground; thus, they were not included in the FE model, assuming at the top of the abutments the same motion of the ground.

Fig. 3: Scheme of the degree of freedom of the load bearings.

3.2. Nonlinear time history analyses The seismic performance of the bridge was evaluated via nonlinear dynamic time history analyses. The seismic hazard was estimated for a nominal life of 100 years, assuming an ordinary structure (nominal life of 50 years) with a class of use IV (strategic constructions), for the life safety (LS) limit state probability of occurrence, corresponding to a return period of 949 years. Sets of accelerograms were selected from the Engineering Strong Motion Database (Luzi et al. 2020) using the REXELweb tool (Sgobba et al. 2019), in order to get a group of seven signals with a mean pseudo-acceleration response spectrum matching the code-conforming LS spectrum (soil category B and flat topography). The accelerogram records used for the nonlinear time history analyses are listed in Table 1.

Table 1. Accelerogram records used in the time-history analyses.

No.

Event (LS set)

Network Station

Mw Rep (km)

PGA (cm/s 2 )

1 EMSC-20140203_0000008

HI

ARG2

6.0

9.6

257 284 163 211 295 220 194

2 GR-1981-0001

HL

XLCA 6.6

35.9 11.3 13.7 11.2 76.3 40.5

3 EMSC-20161026_0000077 4 EMSC-20161026_0000095 5 EMSC-20161026_0000077 6 INT-20230206_0000222 7 INT-20230206_0000222

IT IT IT

NOR NOR NRC

5.5 5.9 5.5 7.5 7.5

TK 3802 TK 4611

The masses considered in the analyses are calculated from self-weight of structural elements and permanent weight of pavements and barriers, assumed equal to 43 kN/m; pier prestressing is taken into account modeling tendons with a cross section of 12.5 cm 2 (9 strands with 15.2 mm diameter), an initial stress equal to 1250 N/mm 2 and total stress losses equal to 375 N/mm 2 (30% of the initial stress) accounting for creep, shrinkage and steel