Brunel’s Bridges

Britain has only a few large rivers and thus, until the Industrial Revolution, presented relatively few opportunites (or demands) for bridges of any great ambition. Most of them were based on simple arched designs and it is broadly true to say that until the late 18th century bridge building in Britain, at its best, remained a long way short of the achievements of the ancient Romans.

This situation started to change in the late 18th century thanks to two main factors. The first was the development of the new turnpike roads and canals which spread across the landscape in the late 18th and early 19th centuries: the engineering profession found themselves required to build great numbers of new bridges. In the early 1800s a number of large and magnificent masonry bridges went up, like John Rennie’s Waterloo Bridge in London (1811 - 17), of Thomas Harrison’s Grosvenor Bridge as Chester (1827 - 33).

The second factor was the development of iron as a bridging material. In 1781 Abraham Darby III opened the world’s first iron bridge at Ironbridge, whose cast-iron sections made up a clear span of 100 feet. As an achievement of design and iron founding it was so ambitious and so far ahead of its time that it was some years before anyone attempted anything comparable. Nevertheless, a barrier had been broken, and in 1796 Thomas Wilson raised the stakes further by completing his astonishing bridge over the Wear at Sunderland, a single cast-iron arch spanning 237 feet. Other fine cast-iron bridges followed on quickly. Canal aqueducts presented a particular opportunity in this respect: the most spectacular example is Jessop’s and Telford’s Pontcysyllte Aqueduct in Denbigshire of 1794 - 1805, a thousand feet long, with its cast-iron trough up to 121 feet above the river. At Pontcysyllte, and in his Menai suspension bridge of 1819 - 26, Telford demonstrated that he was the leader in the field, the foremost road and bridge builder of his age, but several other engineers were working at the frontiers of knowledge too. So when Brunel began designing his railway in 1835 he was operating in a competetive, fast-moving situation, with a lot of new ideas about bridge design and the structural uses of iron in the air.