Briefing: FRP railway decking – Calder Viaduct

Abstract

This paper describes the first known application of fibre-reinforced polymer (FRP) composites for structural re-decking of a railway bridge for full railway and derailment load. Calder Viaduct crosses the River Calder near Sellafield in Cumbria. The original bridge comprised three spans of half-through-type steel girders with timber decking and ballasted rail, constructed in 1922. Due to the coastal location of the viaduct, significant corrosion of the steelwork and deterioration of the timber decking had occurred. This type of timber railway decking on a metallic supporting superstructure is common throughout the UK. The structure was chosen by Network Rail for a pilot project for replacement of the timber decking with FRP composite materials. The chosen FRP decking solution comprised a standard pultruded glass-fibre-reinforced polymer (GFRP) deck with bonded and bolted GFRP top plate for ballast retention and wear resistance. Other types of FRP deck, such as bonded FRP pultruded sections and bespoke vacuum-cured FRP decks, were also considered. The choice of an FRP decking system was driven by a number of factors; ease of installation, adaptability, minimum depth/weight, compliance testing, durability/design life and cost. The installation method, design challenges such as achieving compliance for derailment loading, and procurement issues such as developing a generic specification to enable competition, are discussed. Conclusions are given on the factors that require consideration by the designer to deliver a competitive FRP solution in accordance with best practice, and a brief comparison with equivalent performance steel decking is included.