PSI - Issue 78

Andrea Dhima et al. / Procedia Structural Integrity 78 (2026) 1366–1373

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As for Scenario 1, a corrosion depth of 0.5 mm results in a 30% reduction in concrete strength. Regarding Scenario 2, the area of deteriorated concrete is smaller, and the prestressing reinforcement is affected by localised corrosion. Consequently, its yield strength was appropriately reduced by means of the β s factor, assuming the same value as that applied to the other reinforcement bars. In this scenario, a corrosion penetration of 0.5 mm results in a 20% reduction in concrete strength. The final degradation scenario was intended to simulate the actual condition of the structure, observed during the on-site inspection, by applying the previously described procedure. The objective was to assess the effective structural safety of the prestressed reinforced concrete beams. An examination of the available report and documentation identified a specific section of the beam exhibiting evident signs of degradation, including exposed stirrups and non–prestressed reinforcement, as illustrated in Figure 1c. For this purpose, the assessment involved the comparison with the demand corresponding to the most severe traffic load condition, represented by a design bending moment M Ed,A equal to 18138.27 kNm. This value was compared against the M-N interaction domain for the critical section, allowing the evaluation of the safety index against traffic loads. The analysis indicated that the safety coefficient undergoes a marked reduction, with the resistance decreasing by 15 % under a corrosion penetration of 0.5 mm.

Table 3. Variation in load-bearing capacity of girders with increasing corrosion penetration. M Rd [kNm] Scenario 1 Δ [%] Scenario 2 Δ [%] Scenario 3 Δ [%] M Rd,uncorroded 15582 0 15582 0 15582 0 M X=0,5 mm 10497 32.6 12347 20.8 13314 15 M X=1 mm 9475 39.2 11660 25.2 12784 18 M X=1,5 mm 9046 41.9 11352 27.1 12534 20 M X=2 mm 8814 43.4 11165 28.3 12368 21

For the seismic assessment of the piers in the presence of corrosion, the nonlinear analyses account for the effective properties of the deteriorated steel reinforcement and concrete according to Equations (1) and (3), respectively. The piers shear and bending capacity, calculated for the two principal directions, was initially compared with the acting shear forces obtained from the linear dynamic analysis, revealing a markedly different behaviour (Figure 4). In the Y-direction, corresponding to the bridge transverse direction and longest side of the pier, this exhibits an adequate safety margin against the seismic demand, even when considering various degradation scenarios, whereas in the Z direction, corresponding to the bridge longitudinal direction and pier shortest side, it shows an insufficient shear capacity. This finding reinforces that the fundamental issue lies in the intrinsic structural deficiency in shear, representing a dominant failure mechanism that is characteristic of stocky piers, and is further exacerbated by degradation.

Fig. 4. Effect of degradation on piers shear and bending capacity: reduction in safety factors with increasing corrosion penetration.

Nonlinear dynamic analyses were also conducted using sets of spectrum-compatible accelerograms to better evaluate the structural behaviour of the viaduct piers subjected to seismic loading. The results of the analysis using the shear hinge model confirm a direct correlation between the level of degradation and the earlier onset of shear