The Birth of Prestressing? Iron Bridges for Railways 1830 to 1850

The new railways in Robert Stephenson's day needed many slim bridges with flat soffits. Simple cast iron beams sufficed for short spans but problems arose with jointing of castings for longer ones. A solution, with wrought iron ties added to bolted castings, seemed ideal and was widely adopted. The misconception with this scheme was not realised until after the disastrous failure of Stephenson's Dee Bridge at Chester in 1847. A major inquiry followed and extensive remedial work. New bridge forms emerged, notably Fairbairn's ungainly wrought plate girders. Charles Wild's development from the failed system was another. Here Wild successfully used the principle of prestressing on cast iron, some 80 years before Freyssinet 'introduced' it with concrete in the 1930s. Fairbairn's thinking had a wide following but the only application of Wild's design was his neatly detailed bridge over the Arno. Was Wild too far ahead of his time?