Detail of the arches and roadway. Image source: Woodward, Calvin Milton. A History of the St. Louis Bridge. St. Louis, G. I. Jones and Company, 1881, pl. 19.

Centuries of Civil Engineering

A Rare Book Exhibition Celebrating the Heritage of Civil Engineering

Bridges of the British Isles

The Menai Suspension Bridge

Suspension bridges go back to the beginnings of human culture, but stiffened suspension bridges were not introduced until the early 19th century, by an American, James Finley. Thomas Telford, one of the great civil engineers of England, showed the potential of the suspension bridge when he successfully crossed the Menai Straits, which lie between Wales and Anglesea, on the route of the London-Dublin mail. The bridge was begun in 1819 and opened for traffic in 1826. The roadbed is suspended from sixteen chains, in sets of four; each chain is made up of flat wrought iron eyebar links that are eight feet long. The links were made under Telford’s supervision in the Shropshire iron works of William Hazeldine. Each link was dipped in hot linseed oil after forging, to prevent rusting.

With a central span of 580 feet, the Menai bridge was the longest clear span in the world when it was completed.

Menai Suspension Bridge. Image source: Telford, Thomas. Life of Thomas Telford, Civil Engineer. Ed. by John Rickman. Atlas, London: Payne and Foss, 1838, pl. 70.

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Britannia Bridge

The Menai Straits had been spectacularly bridged in 1826 by Thomas Telford, with what was then the world’s longest suspension bridge. The purpose was to carry the mail between Ireland and London, and it did its job well, as long as the mail was carried by coach. But by the 1840s railways were taking over from road carriages, and it was thought that a suspension bridge could not carry the load of a train. So Robert Stephenson was commissioned to bridge the straits again. It was his idea to construct a tubular bridge, which would provide the needed stability. It was originally thought that the tubes would need to be supported by suspension chains, but elaborate testing by William Fairbairn showed that the chains were unnecessary. The central tower, which supported the tubes, was built on Britannia Rock, hence the bridge was named the Britannia Bridge. This view shows the completed Britannia bridge in the foreground, with Telford’s 1826 suspension bridge visible in the background.

Crossing the Menai Straits to the Isle of Anglesey. Image source: Knight, Edward Henry. Knight's American Mechanical Dictionary. Vol. 3, New York, Hurd and Houghton, 1877 [c1876], frontispiece.

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The tubes for the Britannia bridge were built on staging on the shore, upriver of the bridge. There were four tubes required in all, each one 470 feet long, and weighing 1300 tons apiece. The tubes were fabricated of wrought iron plate that was hand-riveted together, some 800,000 rivets being used in each tube. Work began in June, 1847, and within a year the first tube was finished. It was floated into position on pontoons in June, 1849.

Detail of a tube under construction. Image source: Clark, Edwin, and Robert Stephenson. The Britannia and Conway Tubular Bridges. Atlas, London: Published for the Author, by Day and Son [etc.], 1850, pl. 3.

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Positioning tubes on the Britannia Bridge. Image source: Tomlinson, Charles. Cyclopædia of Useful Arts, Mechanical and Chemical, Manufactures, Mining, and Engineering. Vol. 1, London, New York, G. Virtue & co., 1854, p. 247.

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After the tubes for the Britannia Bridge were completed, they were floated into position between the towers on pontoons. The towers had vertical channels built into them to accommodate the ends of the tubes. The wood engravings in this encyclopedia article show how the tubes were floated and placed in position. The first illustration shows the main Britannia tower, with one set of tubes already raised and the masonry filled in, and a third tube about half-way up the tower. The second illustration is a scenic view of a tube floating on eight pontoons to its position next to the tower. 

Scenic view of a tube floating into position. Image source: Tomlinson, Charles. Cyclopædia of Useful Arts, Mechanical and Chemical, Manufactures, Mining, and Engineering. Vol. 1, London, New York, G. Virtue & co., 1854, p. 247.

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The tubes for the Britannia Bridge were raised into position by hydraulic presses. The presses were mounted at the top of the towers and connected to the floating tubes by chains of wrought iron links. The length of throw of the hydraulic presses was exactly the same as the length of the chain links, so when the press reached the top of its travel, the tubes were wedged into position, a set of links was removed from each chain, and the press was reset. As a safety precaution, the masonry below the tubes was filled in as the tubes were raised, which proved wise, for on one occasion the hydraulic engine failed and the tube dropped, but because of the masonry support, it fell only a few inches and was undamaged.

Hydraulic press and wrought iron chains for lifting the tubes. Image source: Dempsey, George Drysdale. Tubular and Other Iron Girder Bridges, Particularly Describing the Britannia and Conway Tubular Bridges. London, John Weale, 1850, pp. 128-129.

Hydraulic press and wrought iron chains for lifting the tubes. Image source: Dempsey, George Drysdale. Tubular and Other Iron Girder Bridges, Particularly Describing the Britannia and Conway Tubular Bridges. London, John Weale, 1850, pp. 128-129.

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Forth Bridge

The great Forth railway bridge was not the first cantilever bridge to be built, but it was certainly the longest. Designed by Benjamin Baker to bridge the Firth of Forth in Scotland, it utilized three towers, with cantilever arches extending from each. The result was two clear spans of 1700 feet each, almost four times as great as the span of the Britannia bridge. Baker used trusses made of tubular steel, which gave the bridge both its strength and its impressive appearance

The illustration, from the British journal Engineering, shows the bridge just before the completion of the central girders, which connected the great cantilever trusses.

The Forth Bridge nearing completing of the central girders. Image source: Westhofen, W. The Forth Bridge / Reprinted from "Engineering", February 28, 1890. 3rd ed, revised. London. Offices of "Engineering" [1890?], pl. 18.

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