Description
A large number of masonry bridges constructed in Europe during the Industrial Revolution are still in service. Continuous operation for far more than a century and weathering effects have contributed to material degradation in the main bridge components. To ensure that old masonry bridges remain safe even under increasing traffic loading, it is important to identify potential deterioration in bridge performance before the development of critical irreversible damage. This task can be accomplished via periodic monitoring of the bridge response under traffic loading. Digital Image Correlation (DIC) is currently used as an effective non-contact method to measure displacements and strains in physical testing. Most of the applications are in laboratory settings, but DIC techniques have yet to be extensively applied to field monitoring. This paper showcases the potential of DIC monitoring for serviceability assessment of masonry bridges. Some results of an extensive monitoring program on railway viaducts in the UK are presented and critically discussed. Structures with different geometrical characteristics, including different pier heights, span lengths and span-to-rise ratios and made of different masonry materials have been investigated. The results obtained using specific targets attached to the monitored structures or using the actual masonry texture and bond characteristics as natural targets have been compared, and the effects of environmental effects (rain, wind) and monitoring sites (urban and rural environment) have been assessed considering also the influence of cameras characteristics and settings. In all scenarios, suitable monitoring data were mostly obtained. A significant influence of the camera depth of field has been established, especially when measuring deflections at different locations on the intrados of the arch barrel. Strategies to mitigate the detrimental effects of environmental noises, which are quite significant especially when monitoring in challenging environmental conditions, are also proposed.
