The world’s first iron bridge was built across the River Severn near Telford, designed by architect Thomas Farnolls Pritchard of Shrewsbury. The work was completed in 1779 and the bridge opened to traffic in 1781. Today, it is considered an icon of Britain’s industrial revolution, and since 1986 it has been a UNESCO World Heritage Site.
The Iron Bridge spans 30 metres, and used a total of 378 tons of iron. The arched structure comprises of five main semi-circular ribs which were made individually and joined together with techniques borrowed from carpentry, such as dovetail and shouldered joints. The bridge was closed to vehicles in 1934.
Over the years, the bridge has undergone extensive repairs and strengthening work. In 1973, a reinforced concrete strut was built beneath the river bed to counter the inward pressure of the bridge abutments. The road surface was replaced with lighter tarmac, the stone abutments repaired, and the toll-house repurposed as an information point.
Between 1999 and 2000, English Heritage carried out a full survey of the bridge and produced a three-dimensional digital record, which still informs the current management of the structure. In 2018, the charity carried out a major conservation project to rectify damage from ground movement, including an earthquake in the 1890’s.
Morgan Cowles, English Heritage Head of Conservation Maintenance, said: ‘After it was built cast iron came to be widely used in bridges, aqueducts and buildings. For me it represents a pivotal moment in development of metallurgic design and engineering.’
300 bespoke iron wedges were cast to replace existing ironwork which had suffered from stresses over time. After the structural repairs were completed, a team of six painters applied 2,400 litres of red-brown paint to the bridge, after research revealed that this was its original colour.
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