Seasonality of Behaviour and Deterioration of Condition in an Ageing, Damaged Masonry Railway Bridge

Ageing masonry bridges make up approximately half of bridge spans on the roads and railways of the UK, with an estimated 200,000 such structures across Europe. These historic investments in embodied carbon often also hold architectural or industrial heritage value, making their preservation and ongoing, optimised use a pressing concern for today’s structural engineers and asset managers. Targeted insights from monitoring technologies can assist this process, by improving decision makers’ understanding of structural condition and deterioration. However, for this to be successful, seasonality and variability under environmental and operational variables must first be understood. This paper reports new insights from a combined fibre-optic Fibre Bragg Grating (FBG) and Acoustic Emission (AE) sensing installation at an early-20th Century, masonry arch railway bridge. The skewed, three span bridge displays four notable transverse fractures that threaten to undermine its safe performance and motivated this monitoring campaign. Its construction is in brick masonry, above which the fill material is believed to be the same high-plasticity London clay that has been used extensively to build earthwork embankments in this region. Monitoring results have enabled a detailed understanding of typical bridge response and its sensitivity over time, particularly to temperature and water content in the clay backfill. Decoupling these drivers of response variability has led to novel findings regarding the environmentally-driven deterioration of masonry bridges under working loads, with implications for maintenance prioritisation across the rail network.