Keywords: railway, bridges, glass fibre reinforced polymer, analysis, design, installation.

Network Rail are the infrastructure owners and maintainers for approximately 40,000 bridges. A large proportion of the bridgestock comprises metallic railway bridges with timber decking carrying ballasted track. The substructure and metallic structural elements of this bridgestock are typically 100 years old with limited total capacity, no available additional construction depth, and minimum ballast depth (150-300mm). Timber decking typically has a serviceable life of up to 30 years and is known to worsen the durability of steelwork because of moisture retention. Steel decking may be used to replace timber decking but has associated issues of galvanic corrosion and also those related to transportation, access and installation of heavy steel panels.

In addition to the development of fibre reinforced polymer (FRP) bridges since the 1980s, FRP railway decking has recently been developed, designed and constructed to replace life expired timber decking in the United Kingdom. The use of FRP decking significantly reduces the selfweight of the decking (by 50% compared to equivalent steel decking), is shallower than existing timber decking allowing ballast depth to be improved, and is quicker to install as larger panels can be lifted because of the reduced selfweight. The material cost of FRP decking is currently greater than that of timber or steel decking, however, where access is difficult and railway possession duration is limited the benefits of reduced installation costs can give a competitive overall cost. The durability of FRP materials is also generally recognised to be better than that of painted or galvanised steel and timber.

The development of suitable FRP decking is discussed based on three case studies where FRP decking with derailment capacity was designed as a replacement for timber decking on metallic railway bridges, including the world first application of FRP railway decking. The case studies comprise half-through type metallic bridges with cross-girders and timber decking, with a total length of up to 50m. In each case a replacement FRP decking system was designed based on a heavy duty glass fibre reinforced polymer (GFRP) grating system with bonded GFRP top plates (and in some cases bottom plates for additional strength and stiffness), spanning up to 1.25m with a total depth less than 100mm. The case studies show the benefits of using FRP railway decking which include lightweight (allowing craned installation of large pre-fabricated deck panels) and speed of installation.

Recent developments are described that will enable improvements in technical performance and reduced material and installed cost. These developments include a deeper grating section allowing spans of up to 1.5m together with variable grating spacing, and a new optimised grating section currently being tested for derailment loading.

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