An article written by CSIC Research Associates Liam Butler and Nicky de Battista that highlights the benefits of installing fibre optic sensors in rail infrastructure has been published in industry title Rail Technology Magazine (RTM).
Two self-sensing prototype bridges were completed as part of the Stafford Area Improvements Programme, a £250m award-winning rail redevelopment project on the West Coast Main Line near Stafford. The bridges were instrumented and monitored by CSIC during the various construction stages with fibre optic monitoring systems capable of providing information required for real-time capability assessment.
“Given the overall potential of fibre optic sensing technology to enable data-driven approaches to design, construction and maintenance, it is foreseeable that future infrastructure projects such as HS2 and Crossrail 2 may adopt these technologies as standard permanent instrumentation,” said Dr Liam Butler.
Bridge inspections represent a multi-million pound investment by both highways and railway authorities. As well as the cost, visual and tactile inspections present risk to operators, are limited to providing condition-based information (with no quantitative link to remaining capacity) and may not capture the condition of critical elements which can be hidden or inaccessible
There is pressing need for monitoring systems and data analysis tools capable of providing the information required to assess structural capability remotely and in real time to reduce the frequency of visual inspections. Developing a monitoring system able to assess the effect of increased or abnormal loads on the structure could help to identify points of intervention and reduce the need for additional repairs or strengthening.
CSIC has been developing fibre optic sensing technology for monitoring civil infrastructure, including distributed fibre optic sensing (DFOS) and fibre Bragg gratings (FBG), for the past six years. “Fibre optic sensors provide several advantages over traditional instrumentation. A single optical fibre can provide tens (in the case of FBGs) or thousand (in the case of DFOS) of sensing points, all from a single fibre optic cable,” said Dr Nicky de Battista.
“Since the optical fibres only carry light signals, rather than electricity, the sensors are immune to electromagnetic interference and are intrinsically safe. The optical fibres are composed of glass which is inert and therefore will not corrode or deteriorate over time, thus providing sensing capability throughout the lifetime of a structure.”
The main focus of this project was to use sensor data as a means of tracking the entire load history – from the start of construction of the bridges and throughout their service lives. Data from sensors are currently being acquired and processed on a monthly basis. In addition sensors were installed during the manufacturing process of prestressed concrete sleepers in order to track the load path from the axles, through the rail, into the sleepers, through the ballast and into the bridge superstructure. This instrumentation has also provided axle, bogie and train-specific information including train speed, direction and axle spacing, enabling a better understanding of material behaviour, fabrication techniques and the effect of environmental conditions on sleeper performance.
Instrumentation of the two bridges was completed in April 2016 and they will continue to serve as significant demonstrators for the use of fibre optic sensing technology.
Read the full article here.
Related publications
Butler LJ, Xu J, Ping H, Gibbons N, Dirar S, Middleton CR, and Elshafie MZEB (2017). Robust fibre-optic sensor arrays for monitoring early-age performance of mass-produced concrete railway sleepers. Journal of Structural Health Monitoring. Online ahead of print. DOI: 10.1177/1475921717714615.
Butler LJ, Gibbons N, Ping H, Elshafie MZEB, and Middleton CR (2016). Evaluating the early-age behaviour of full-scale prestressed concrete beams using distributed and discrete fibre optic sensors. Journal of Construction and Building Materials, 126: 894 – 912. https://doi.org/10.1016/j.conbuildmat.2016.09.086
Butler LJ, Gibbons N, Middleton CR, Elshafie MZEB (2016). Integrated Fibre-Optic Sensor Networks as Tools for Monitoring Strain Development in Bridges during Construction. The 19th Congress of IABSE Proceedings, Stockholm, September 21 – 23, 2016:1767 – 1775.