Wednesday, July 4, 2007

Ironbridge, Coalbrookdale - Shropshire, England

Coalbrookdale is regarded by many as the birthplace of the Industrial Revolution. The town of Ironbridge on the eastern bank of the River Severn is the location of the world’s first metal bridge. Designed in 1775, the gracefully arching prefabricated cast-iron structure, appropriately named Ironbridge, was fixed to its masonry abutments in the summer of 1779. Spanning 100 feet (30 meters), the bridge supports itself without a bolt or a rivet in the entire structure! In terms of the creative application of new materials and technology, it remains one of history’s great architectural and engineering feats, the product of the fervent inventiveness of optimistic industrialists, opening the way to the modern era of iron- and steel-framed buildings.

Coal and limestone mining and iron smelting made the River Severn, which reaches the sea through the Bristol Channel on England’s west coast, one of Europe’s busiest waterways. In 1638 one Basil Brooke patented an iron-making process and built a furnace at Coalbrookdale. Seventy years later the operation was acquired and overhauled by the entrepreneurial Bristol Quaker Abraham Darby I, an ironmonger and brass founder. In 1711 he developed a cheaper means of smelting iron by using coked coal as fuel rather than charcoal. The process liberated iron production from fuel restrictions—industrialization initially meant deforestation—as well as making very large castings possible.

Within a couple of years Darby and his partner, Richard Ford, developed what was a minor business producing mainly pots and pans into the world’s leading ironworks. After a few decades the Coalbrookdale Company and its subsidiary Lilleshall Company had expanded to own mines, forges, factories, and farms throughout the region. The burgeoning iron-, brick-, and pottery works in the parishes of Madeley and Broseley, facing each other across the Severn Gorge, brought workers flocking to the district. That dramatic population growth and the obvious increase of commercial and industrial traffic meant that the local ferry, precariously approached down steep, slippery banks, soon proved inadequate for local needs.

Abraham Darby II had proposed to bridge the Severn between Madeley Wood and Benthall but the project lapsed when he died in 1763. It was left to his son, Abraham III, to carry out the project. With the eager cooperation of the squire of Broseley, ironmaster John Wilkinson, in 1775 young Darby convened a meeting of potential subscribers to plan a bridge. The group obtained Parliament’s approval for a structure of “cast-iron, stone, brick or timber.”

The world’s first cast-iron bridge was designed by the Shrewsbury architect Thomas Farnolls Pritchard, who two years before had suggested using the new material for such projects. He proposed a single-span bridge, estimated to cost £3,200, because intermediate piers would obstruct traffic on the busy river. Work began in November 1777. When Pritchard died in that year, Darby assumed responsibility for completion. The components were cast in the Upper or Lower Furnace at Coalbrookdale during the winter of 1778–1779, ready for erection the following summer. Some of the castings—there were 453 tons (384 tonnes) in all—were almost 80 feet (25.5 meters) long, and the Coalbrookdale Works had to be altered to accommodate production. Beginning in May 1799, the prefabricated iron structure took only three months to put together. The parts were ingeniously designed to allow assembly simply by fitting projections into slots and tightening the joints with cast-iron wedges—a totally interlocking structure that, as noted, has no riveted or bolted connections. Ironbridge is a semicircular arch of 100 feet, 6 inches (30.5 meters) span, made by joining two half-arches that were each cast as a single piece. It supports a 24-foot-wide (7.3-meter) deck 40 feet (12 meters) above the Severn.

Costing about twice as much as first estimated, it was opened as a toll bridge (to recoup some of the expense) on New Year’s Day 1781. Within three years earth movement caused some noncritical cracking in the ironwork. The bridge survived a severe flood in 1795, and in 1802 the masonry abutments were replaced by timber. In turn those were replaced by the cast-iron arches that one sees today. Doubts about the stability of Ironbridge led to suggestions about demolition in 1926 but nothing happened. In 1934 it was closed to vehicles and listed as a historical monument. The Shropshire County Council assumed ownership in 1950, and extensive restoration was undertaken in the 1970s. The bridge now comes under the control of English Heritage. In 1986 UNESCO designated the Ironbridge Gorge a World Heritage Site, noting that “all the elements of progress developed in an eighteenth century industrial region can be found [there]. … The blast furnace of Coalbrookdale … is a reminder of the discovery of coke, which, together with the bridge at Ironbridge, the first metallic bridge in the world, had considerable influence on the evolution of technology and architecture.”

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