Sunday, July 27, 2008
Clifton Suspension Bridge
The River Avon rises in the Cotswolds and falls about 500 feet (150 meters) in its 75-mile (120-kilometer) course to the Severn Estuary at Avonmouth. Near Bristol it passes through a channel that was cut in the nineteenth century to give access to oceangoing vessels, and then through the steep Clifton Gorge, where it is daringly crossed by the Clifton Suspension Bridge, 245 feet (75 meters) above the water. The iron structure, with a main span of 702 feet (214 meters), challenged conventional wisdom and pushed the new material and contemporary technology beyond the theoretical limits.
Bristol’s port of Avonmouth was a well-established center for coastwise and international shipping. As the nineteenth century saw accelerating growth in trade and economic prosperity, Bristol’s wealthier citizens wished to secure a market share for their city, and the renown that went with it, in the face of intense competition from such rivals as Liverpool. Perhaps they envied the prestigious bridge at (Conwy, Wales, and the Menai Suspension Bridge, both designed by the Scots engineer Thomas Telford. Funds were in hand to start the project: the Bristol wine merchant William Vick, who died in 1754, had bequeathed £1,000 to build a bridge across Clifton Gorge; the money had been accruing interest while held in trust.
A design competition, announced in May 1830, attracted twenty-two entries, including four from the brilliant engineer Isambard Kingdom Brunel, who was then only twenty-four years old. The spans he proposed varied between 879 and 916 feet (267 and 279 meters); all were longer than any existing suspension bridge. The jury short-listed four designs (one of Brunel’s among them), before seeking Telford’s opinion. In an arrogant gesture he rejected all the schemes. His given reason was pragmatic enough: his Menai bridge (1819–1826) had almost been destroyed by crosswinds; it was nearly 579 feet (175 meters) long, and Telford believed that nothing over 600 feet (184 meters) was feasible—the 700 feet across the exposed Clifton Gorge was out of the question. The committee then asked him to submit an alternative design, but the three-span bridge carried on soaring Gothic spires that he produced was unsuitable, even comical. A second competition followed in October 1830, and Telford resubmitted that design, only to see it again rejected. The twelve entries were reduced to four finalists, and Brunel’s proposal, modified so that the main span was only 630 feet (192 meters), was placed second. He went to Bristol to meet the committee and convinced them with arguments about the practicalities and the esthetic quality of his tower design. He was appointed as engineer in 1831.
Brunel had an eye for the stunning landscape, with its high wooded cliffs, and his “Egyptian” towers, although not his favorite stylistic alternative, complemented the drama of the place. He had intended to have them inscribed with hieroglyphs and crowned with sphinxes, but the cost was prohibitive. There were delays for other reasons, including the 1831 Bristol riots associated with the Reform Bill, but lack of funds was the main problem. Work did not start until 1836. More financial shortfalls caused an interruption in 1853, and the piers stood untouched for some years, even being threatened with demolition. Reusing chains from another of Brunel’s works, the demolished Hungerford Suspension Bridge (1841–1845) in London, the Clifton Suspension Bridge was finally opened in 1864, although the original design was not followed completely. Brunel had died five years earlier.