3D digital image correlation for field assessment of masonry arch bridges

Masonry arch bridges with observed or suspected defects require effective structural health monitoring to ensure their safety under increasing traffic loads. Traditional methods, such as visual inspections, provide only qualitative assessments and do not capture the variations in key local and global response characteristics under traffic loading. More advanced structural health monitoring techniques can measure the variations in displacements and strain fields under traffic; however, they typically require contact sensors and partial or complete occupation of the monitored spans. This study examines, for the first time, the application of 3D Digital Image Correlation (DIC) as a non-invasive method for monitoring masonry arch bridges in the field. It offers a refined 3D DIC monitoring technique specifically designed for such structures under traffic loading, providing improved accuracy through various error mitigation strategies. Using a case study of the Mill Road Viaduct, a multi-span railway bridge in Lewisham (London, UK), 3D DIC effectively captured full-field displacements and crack openings caused by live traffic loads. The results revealed significant 3D effects, particularly in the arch barrel, and confirmed crack development in different directions, highlighting the superiority of 3D DIC monitoring over the conventional 2D DIC counterpart. The accuracy of the 3D DIC measurements was validated against 3D scanning data, demonstrating its reliability for bridge monitoring applications. Despite its advantages, factors such as camera stability, environmental noise and calibration complexities are identified in this paper as critical challenges that should be addressed for successful deployment in the field. This study highlights 3D DIC as a real-time, high-resolution structural monitoring tool, offering valuable insights for proactive maintenance strategies. • Advanced real-time monitoring for masonry bridges using 3D DIC. • Tracking the complete 3D displacement field and cracking under traffic loading. • 3D DIC is applied to monitor a real railway viaduct in service. • 3D DIC measurements are validated against 3D scanning data. • Results show significant 3D effects and the development of cracking along different directions in the masonry arch barrels.