Conwy Railway Bridge: The Last Surviving Wrought-Iron Tubular Bridge

The Conwy Railway Bridge carries the North Wales coast railway line across the River Conwy between Llandudno Junction and the town of Conwy. Built in the 19th century, the wrought iron tubular bridge is now a Grade I listed structure and a scheduled monument. It is the last surviving example of a tubular bridge design by Robert Stephenson, following the destruction and rebuilding of the original Britannia Bridge across the Menai Strait in 1970.

Originally, the plan for the crossing was a suspension bridge to complement Thomas Telford's Conwy Suspension Bridge of 1826. However, Stephenson and his collaborators, including William Fairbairn and Eaton Hodgkinson, determined that a suspension bridge was unsuitable for trains. They instead developed a wrought-iron box-girder structure. This design featured a tunnel-like rigid tube suspended above the river, which possessed sufficient rigidity to be self-supporting over the span.

Groundwork for the bridge began in May 1846. Architect Francis Thompson dressed the pylons as barbicans with crenellated turrets, arrow slits and bartizans to complement the nearby Conwy Castle. While the design included elaborate decorations meant to resemble castle walls, these were abandoned due to expense and extra weight. To build the bridge, the 129.2-meter long tubes were constructed onshore using shipbuilding techniques. They were then attached to pontoons, floated along the river, and jacked into position using steam-powered hydraulic engines. The bridge was officially opened in 1849.

Sources: Wikipedia, OpenStreetMap, Wikidata, Wikimedia Commons