Monitoring and analysis of existing post-tensioned bridge using FBG sensors

Administrators today face the challenge of assessing existing prestressed bridges. In Europe, many of these structures were designed and constructed in the post-war era. Unfortunately, early prestressed bridges are often associated with conceptual errors, such as inadequate protection of the prestressing steel. As a result, it is essential to verify the structural response while considering all factors that may negatively impact the residual prestressing value. This paper presents a case study involving a static load test monitored by modern fibre Bragg grating (FBG) sensors. The analysis focused on a three-span, double-cell box girder, post-tensioned bridge built in 1966. A diagnostic survey and static load test were conducted during rehabilitation after several prestressing wires were damaged. The primary goal was to study the structure’s behaviour under static load from 30-ton heavy vehicles. In this context, in-situ measurements were used to simulate the heavy pavement mechanisms associated with construction activities. The observed responses included deflections, strains, and temperature. The test results showed good agreement with the numerical analysis, indicating a linear response of the structure, with no additional wire breakage observed. Notably, thermal loads had a greater impact than static loads during the test. Long-term monitoring revealed that strain variations throughout the day fluctuated by approximately ±20–25 με, while the external load induced a maximum strain of 12 με. In conclusion, it was recommended to allow the bridge to operate under real-time monitoring, enabling the mechanisms to function effectively.