PSI - Issue 78

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

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due to the uniform and widespread nature of the investigated scenarios, a clear correlation emerges between degradation and the increase in the natural periods, indicating a gradual reduction in global stiffness. The first mode shows the most significant variation, with an increase in period of approximately 6%. Modes 2 and 3 also exhibit an increase, although to a lesser extent.

Fig.5. Variation of the natural periods with increasing degradation.

It is worth noting that the rate of increase in the periods tends to stabilise after approximately 50 years, suggesting a nonlinear relationship between damage progression and its influence on dynamic properties. This larger increase observed in the early years may be attributed to the initial degradation mechanisms, in particular carbonation and the subsequent onset of reinforcement corrosion, leading to a more pronounced reduction in structural stiffness. 5.2. Influence of degradation on structural capacity Figure 6 illustrates the evolution of the load bearing capacity compared to the applied loads, while Figure 7 shows the variation of the safety factor as degradation progresses. In particular, Figure 6a and 6b compares the applied demands and the structural capacity of each pier at different time stages, focusing on bending moment and shear, respectively. A gradual reduction in capacity is observed due to increasing degradation. The demands remain constant, indicating that structural safety is primarily compromised by the loss of resistance rather than by an increase in seismic demand due to the variation in modal properties.

(a) (b) Fig.6. Effect of degradation over time: (a) variation of applied and resistant moment; (b) variation of applied and resistant shear.