Stress corrosion cracking (SCC) is active in some prestressed concrete bridges built in Germany until the 1990s. SCC causes successive brittle failures of the prestressing steel wires. The presence of active SCC is not visible on the surface during routine inspections (which are performed manually at regular intervals). The only visible characteristic symptom that can be observed by inspection personnel is the growth of surface cracks. However, the growth of these cracks is highly unreliable because cracks might be recorded as generally cracked and crack widths are measured with large uncertainties. In addition, concrete surface cracks may not form at all or may form in inaccessible areas of the structure. In the worst case, the entire structure could collapse without warning, as in the Carola Bridge incident in Dresden in September 2024, where the bridge suddenly collapsed. This incident demonstrates the inadequacy of the current inspection approach and the need to monitor structures with SCC risk for safe operation.

One approach to detecting new tendon wire breaks is acoustic emission monitoring, which is based on the characteristic sound that is emitted by a breaking prestressing wire. Another recent and promising approach is to employ distributed strain sensing (DSS). Distributed fiber optic sensors (DFOS) can measure local strain changes along extended lengths with high sensitivity, enabling monitoring of (i) deformation, (ii) redistribution of force, or (iii) cracks with accurate crack width estimation.

This contribution will present experiments on prestressing wire breakage in large-scale prestressed concrete girders. The girders were instrumented with DFOS and the tendon wires were cut. The results indicate that even small pre-stressing losses cause visible changes obtained by DSS data. Based on these results, this contribution discusses the detectability, the evaluation of these strain increments and the potential of DFOS based structural health monitoring applications for concrete structures with the risk of SCC.