PSI - Issue 78

Gregory Santilli Di Luia et al. / Procedia Structural Integrity 78 (2026) 1513–1520

1519

Figures 7a and 7b show the evolution of the safety factor with respect to flexural and shear demand, respectively. Even in the absence of degradation (i.e., assuming the structure is fully intact), the capacity of the structure is insufficient considering the flexural demand, leading to a safety factor lower than 1. This is primarily due to the original design loads at the time of construction, which were significantly lower than the ones considered by the current Standards. As for shear forces, the piers satisfy verification criteria only in a non-degraded state. However, given that the viaduct has now reached 50 years and exhibits evident signs of deterioration, the safety factor, particularly for Piers 1 and 4, has drastically decreased, falling below unity. Overall, the analysis suggests that 50 years of life are reached, the safety factor decreases by approximately 33% for shear actions and 36% for flexural actions.

(a) (b) Fig.7. Effect of degradation over time: (a) variation of the safety factor with respect to bending stresses; (b) variation of the safety factor with respect to shear stresses. 5.3. Influence of degradation on the ductility Figure 8 shows the moment-rotation relationships for a pier shaft section, and how these vary with increasing degradation, using as input one of the nine artificial accelerograms generated from the site’s response spectrum. The different curves represent the time steps considered. The maximum moment substantially reduces over time reaching a reduction of more than 50% in 100 years. Although ductility decreases, the structure retains a good part of its deformation capacity exhibiting only a reduction of around 25% in 100 years. Finally, a significant reduction in the area of the hysteretic loop emerges as degradation increases, which is an indicator of the element's loss of energy dissipation capacity.

Fig.8. Moment-rotation diagram.