Design and construction of a railway flyover at Hitchin, UK

Abstract

A new 837 m long elevated railway has been built at Hitchin in the UK to carry trains between London and Cambridge over the East Coast Main Line. It relieves the main bottleneck at the junction where Cambridge line trains cross the East Coast route on a flat junction. The project involved the design and construction of a 29-span viaduct made of a steel–concrete composite deck, which is effectively composed of 15 jointed structures. Twelve of these are made of two continuous 30 m spans, two structures are made of single, simply supported spans and the remaining length is a continuous three-span structure with a maximum central span of 60 m that crosses the railway at a skew angle of more than 60°. The 425 m curved plan radius alignment was a design challenge as significant torsional effects are caused by the plan curvature, the eccentricity of applied vertical actions, the centrifugal effects and the wind pressures acting on the trains. Steel erection started with the main railway spans, a process that took three overnight possessions due to the curvature, the heavy skew and the geometry of the girders. This paper describes the critical design aspects and the main construction operations of the flyover.