Damage assessment of a railway bridge using fibre optic sensing and lidar data

Skewed masonry arch bridges present a challenge to asset owners because their structural response under traffic loads can be hard to predict. This can be further complicated by damage such as spandrel wall separation cracks, which are common for this type of structure. For skewed masonry bridges in particular, the effect of damage on the load distribution, and therefore on the effective load carrying capacity, is not well understood. This paper presents results from a field investigation of a typical skewed masonry arch railway bridge. Both the current response to train loading and the current geometry, which has likely been affected by long-term deformations resulting from historic loading and damage, are considered. The objectives of the study are to (a) describe and quantify the current structural response, and to (b) investigate long-term deformations over the skewed bridge’s history. The current dynamic response is captured using a distributed network of fibre-optic Fibre Bragg Gratings, arranged in a novel triangular rosette implementation so that detailed time histories of principal strain directions and magnitudes can be mapped across the arch as trains travel overhead. Meanwhile, potential long-term deformation is evaluated through postprocessing of detailed laser scan data and comparison of this point cloud against assumed reference geometries to infer potential movements and mechanisms which could explain these. The methodologies described here allow for possible connections to be investigated between the current behaviour and either long-term mechanisms of deformation or recent intervention work, and for the feasibility of these connections to be commented on