PSI - Issue 84

L. Fieno et al. / Procedia Structural Integrity 84 (2026) 1136–1143

1142

Although the majority of the endoscopic inspections highlighted an excellent state of conservation of the post tensioned tendons and the grouting, in some spans of the viaduct deterioration of the prestressing cables was detected, attributable to strand corrosion or partial loss of bond with the concrete and a reduction in the effective cross-sectional area. This type of deterioration leads to a reduction in the flexural load-carrying capacity of the structure. Accordingly, it was possible to estimate, with adequate safety margins, the residual cross-sectional area of the prestressing steel effectively contributing to flexural resistance. The quantified level of deterioration for each tendon of the examined beam is reported below:

CABLE 1

CABLE 3

CABLE 5

CABLE 7

broken strands= 1 oxidized strands= 4 active strands= 7

broken strands= 0 oxidized strands= 2 active strands= 10

broken strands= 0 oxidized strands= 0 active strands= 12

broken strands= 0 oxidized strands= 0 active strands= 12

Residual Area= 836.1 mm2

Residual Area= 1021.9 mm2

Residual Area= 1114.8 mm2

Residual Area= 1114.8 mm2

% residual= 75% % adopted= 60%

% residual= 92% % adopted= 90%

% residual= 100% % adopted= 100%

% residual= 100% % adopted= 100%

(the tendon does not have proper bond with the concrete) CABLE 2

CABLE 4

CABLE 6

broken strands= 0 oxidized strands= 4 active strands= 8

broken strands= 1 oxidized strands= 6 active strands= 5

broken strands= 0 oxidized strands= 2 active strands= 10

Residual Area= 929 mm2

Residual Area= 743.2 mm2

Residual Area= 1021.9 mm2

% residual= 83% % adopted= 70%

% residual= 67% % adopted= 50%

% residual= 92% % adopted= 90%

Fig. 7. Accurate quantification of degradation

With reference to the midspan cross-section, where the tendon numbering is indicated, a reduction factor for the prestressing reinforcement was assigned to each tendon for use in the ultimate bending moment calculation, based on the extent and severity of the observed deterioration. Tendon no. 1, despite exhibiting a residual area equal to 60% of the nominal area, was excluded from the verification process due to the loss of bond with the concrete. This approach allows for a conservative and consistent estimation of the residual capacity of prestressed elements affected by deterioration of the prestressing steel. 6. Outcomes and Management Actions Following the safety assessments described above, an expert judgment was formulated regarding the management measures necessary to ensure the continued serviceability of the structure. The 2020 Guidelines for Existing Bridges allow a structure to be classified as Adequate, Operational, or Conditionally Operational depending on the load carrying capacity relative to the observed deterioration. An Adequate or Operational viaduct can remain in service without restrictive management measures, whereas a Conditionally Operational viaduct requires such measures, for example in terms of carriageway width and/or vehicle weight limits. Based on the results of the detailed assessments conducted on all the cases examined, expedited safety verifications were required for 28% of the decks, 14% of the piers, and in 12% of the cases the verifications involved both superstructures and substructures. Only 46% of the cases showed a level of degradation that did not compromise the structural safety. In terms of management measures, the analyses conducted required the adoption of new actions in 35% of the cases.