Chepstow Railway Bridge - The Chepstow Bridge Design

The Chepstow Bridge Design

Brunel recognised that a circular cross-section tubular girder — a shallow “bow”, excellent in compression and tension — could be strung by suspension chains to form a stiff, self-supporting structure very much lighter (thus less expensive) than a Stephenson-type box girder. Instead of hanging the chains from towers and suspending the bridge deck from them, Brunel used the chains to stress and slightly bow the tubes, which were braced against the chains using struts. The bridge deck was rigid, because it was effectively clamped against the tubes by the chains. Brunel solved the problem in his own way, and for more than 100 years, the Chepstow and subsequently the Royal Albert Bridge were the only suspension bridges on the British railway system.

In spite of their apparent rivalry, Brunel and Stephenson were great personal friends, to the extent that they supported each other professionally. When Stephenson was under pressure during the enquiry following the collapse of his cast-iron girder bridge over the River Dee killing several people, Brunel did not desert him. In spite of his extreme distrust of the use of cast-iron girders for such purposes, Brunel refused to condemn them when cross-examined as an expert witness. He was also present to provide Stephenson moral support, when the great Britannia box-girders were floated across the river prior to being jacked up to their final positions. So when it came to the revolutionary design at Chepstow, The Times of 24 February 1852, reported that “Mr Stephenson, the eminent engineer, has examined the (great railway) bridge (at Chepstow) and concurred in the plan adopted by Mr Brunel...”.

The bridge was a triumph of the application of a radical design to a specific problem using available materials. The total cost (£77,000) was half what the Conwy bridge cost (£145,190 18s 0d) — admittedly with a main span of only 300 feet (91 m) compared with Conwy's 400 feet (120 m), but there were no deep-water foundations needed at Conwy, and at Chepstow, the cost included a further 300 feet (91 m) of land spans.

With regard to the appearance of the bridge, the Illustrated London News stated that "the peculiarity of the site did not permit any display of 'Art' - that is, of architectural embellishment; indeed, a pure taste rejects any attempt to decorate a large mechanical work with sham columns, pilasters, and small ornamental details."

The bridge was constructed on site for Brunel by Edward Finch of Liverpool as partner in the firm Finch & Willey. After it was completed, Finch remained in Chepstow, and developed a major engineering and, later, shipbuilding business on the site, beside the river. The adjoining site, now occupied by the engineering firm Mabey Bridge (formerly Fairfield Mabey), is still (as of 2012) engaged in prefabricated bridge construction, and in 1987 was responsible for building the A48 road bridge which now runs alongside the railway bridge.