The Chepstow Bridge

The success of the first world’s fair, the Great Exhibition in London in 1851, prompted France to organise its own in 1855. Despite the protectionist attitude of the French government, the United Kingdom took part on a massive scale and again demonstrated its technological lead. Two of the railway engineering models shown by the British contingent were particularly admired: the Britannia and Chepstow bridges. Both made novel and daring use of gigantic tubes composed of riveted sheet metal panels, whose lightness and solidity had been demonstrated by William Fairbairn in the 1830s. For the Britannia Bridge, opened in 1850, the engineer Robert Stephenson, assisted by Fairbairn, passed each railway track through a square, self-supporting steel tube 4 × 8 metres in section. The bridge consists of two tubes 461 metres long, resting on three masonry piers forming arches with a span of 80 to 140 metres. For the Chepstow Bridge, built between 1850 and 1852, Isambard Kingdom Brunel used two steel tubes 2.74 metres in diameter resting on two vertical structures 90 metres apart. Each track is suspended from one of the tubes by tubes braced with diagonal struts. The ensemble forms a large lattice span, extended by two other 30-metre spans. Charles Nepveu’s donation of these two models to the Conservatoire in 1857 bears testimony to French and English engineers’ mutual interest in each other’s work. Nepveu was known in England for his work on bridge foundations.