Long-term monitoring of externally prestressed concrete bridges using semi-closed elasto-magnetic sensors

The effectiveness of external reinforcement significantly influences the durability and safety of bridges. During construction, prestress is typically applied and controlled using hydraulic jacks. However, long-term service conditions may lead to sectional deterioration or wire fractures in external tendons, which often remain undetected due to the absence of effective monitoring techniques. Since non-destructive methods should be applied to obtain the condition of external tendons for long-term monitoring, and considering the limitations of anchor tendon gauges and vibration-based methods, this research implemented a novel study for long-term monitoring and analysis of tendons in externally prestressed concrete bridges during operation. First, semi-closed elasto-magnetic sensors were deployed on two existing highway viaducts without removing the tendons; Second, prestress loss in bridges with different external prestressing configurations were analyzed using finite element method. Third, data collected over a 12-month period following bridge opening were analyzed under actual traffic loads and with consideration of temperature effects. The results indicate that the prestress values measured by the elasto-magnetic sensors correspond closely with theoretical predictions, demonstrating the suitability of this monitoring approach for practical bridge applications. Furthermore, no significant prestress loss was observed during the monitoring period. • Elasto-magnetic sensors are applied on the steel strand of externally prestressed concrete bridges. • A type of semi-closed elasto-magnetic sensor can be installed in two parts after tensioning and wired together, which significantly reduced the amount of time for sensor production. • Monitoring the long-term changes of the prestress while the bridge is still open to traffic. In-time response can be captured. • Measured results with sensors theoretical results from FEM perform great consistency. • The prestress force in steel strands is analyzed with different temperature and traffic loads during the monitoring period of the bridge.