Chepstow Railway Bridge
Coordinates: 51°38′37.10″N 2°40′1.00″W / 51.6436389°N 2.6669444°W
Chepstow Railway Bridge was built to the instructions of Isambard Kingdom Brunel in 1852. The "Great Tubular Bridge" over the River Wye at Chepstow, which at that point forms the boundary between Wales and England, is considered one of Brunel's major achievements, despite its appearance. It was economical in its use of materials, and would prove to be the design prototype for Brunel's Royal Albert Bridge at Saltash. Although the superstructure has since been replaced, Brunel's tubular iron supports are still in place. It is a Grade II listed structure.
Brunel had to take the two tracks of the South Wales Railway across the River Wye. The Admiralty had insisted on a 300-foot (91 m) clear span over the river, with the bridge a minimum of 50 feet (15 m) above high tide. The span would have to be self-supporting, since although the Gloucestershire side of the river consists of a limestone cliff, the Monmouthshire side is low-lying sedimentary deposit subject to regular flooding. Thus on that side, there was nowhere for an abutment capable of either resisting the outward push of an arch bridge, or the inward pull of a conventional suspension bridge. In any case, neither could be used: an arch bridge would not have met the height and width restrictions imposed by the Admiralty, and suspension bridges were notoriously unfit for carrying railway trains. The concentrated weight caused the chains to deflect, allowing the bridge-deck to ride dangerously up and down. A self-supporting truss bridge was the only option.
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