PSI - Issue 44

Mattia Zizi et al. / Procedia Structural Integrity 44 (2023) 673–680

678

6

Mattia Zizi et al. / Structural Integrity Procedia 00 (2022) 000–000

Fig. 6. Damage in (a) tension and (b) compression at the end of the analysis.

3.2. Results Since the load was applied in force-control, the capacity of the bridge was considered attained when the model was no longer able to withstand any load increment, including the cases in which numerical convergence was not reached. The capacity of the bridge so evaluated against the longitudinal seismic action was about 0.46 g , obtained at a horizontal displacement of the keystone of the central arch of about 3 mm. The failure mode clearly showed the occurrence of plastic hinges at the base of the piers and in the extrados and intrados of the arches, alternatively, which means the activation of a global failure mechanism (Chisari et al., 2021; Como, 2017). The backfill also experienced significantly wide yielded zones. The failure pattern is shown in Fig. 7 by means of a contour view of the tensile plastic strains.

Fig. 7. Tensile plastic strains at the end of the seismic analysis.

3.3. Effects of backfill characteristics on the seismic response In order to assess the effects of the backfill characteristics on the seismic response of the structure and investigate possible retrofitting solutions, a parametric study was performed by varying one-at-a-time: i. the Elastic Modulus of the backfill E b ; ii. the cohesion of the backfill c ; iii. the friction of the contact surface μ ; iv. the friction angle of the backfill φ . The adopted values and obtained results are summarized in Table 1, together with the percentage variation Δ% in terms of strengths exhibited by the different models with respect to the reference model.

Table 1. Results of the parametric analysis. E b [MPa] Δ% c [MPa] Δ%

μ

Δ%

φ [°]

Δ%

25

-4.7% +5.8% +21.4%

0.01

+3.2% +32.8%

tan(15°) tan(60°)

-3.3% +1.8%

20 35

-5.9% -0.7%

100 200

0.1