SUSPENSION BRIDGE is a bridge in which the weight of the roadway, instead of resting upon arches of masonry, or on a rigid framework of wood or iron, is supported by the tension of ropes, chains, or rods.
We have no account of the existence of iron suspension-bridges in Europe before the middle of the last century. The earliest appears to have been a small one built across the river Tees, at an elevation of about CO feet, two miles above Middleton, for foot pas sengers only. The first iron suspension bridge built in America was that constructed in 1790, by Mr. Finlay, across Jacob's Creek, on the road between Union Town and Green burgh, the length of which was about 70 feet. Mr. Finlay subsequently, in 1801, obtained a patent for the construction of such bridges, and built several in the United States ; one of which, over the Schuylkill, was 800 feet long. In 1807 a scheme was proposed by M. Belu, a French engineer, for crossing the Rhine, between Wesel and Ruderich, by a bridge about 820 feet long, to be snpported by a net work of wrought-iron chains. In 1814 a bridge of similar construction was proposed for crossing the Mersey at Runcorn Gap, so as to form a direct communication between Runcorn in Cheshire and Liverpool. In 1818 a suspension:bridge was built across Gala Water, made of thin wires, at a cost of only about 401., although its span was about 111 feet. Another wire bridge of about the same length was built in 1817 across the Tweed, at King's Meadows, at an expense of 1601. Sir Samuel Brown soon afterwards introduced all ,improved method of constructing chains for suspending the roadway. Chains of the ordi nary form, with short links, are very defective in strength ; and several difficulties, among which is the great extent of surface exposed to oxidation, attend the use of cables con sisting of small rods or wires. The plan adopted by Sir S. Brown was to form chains of round or flat bars of iron, several feet long, ha"ving either welded eyes or drilled holes at each end, and being connected toge ther by short links and bolt-pins. The first extensive bridge erected upon this plan was the Union Bridge across the Tweed, near Berwick, opened for use in 1820. The length
is 449 feet, and the deflection is about 30 feet. There are twelve suspending chains, arranged in pairs side by side, and in three tiers, one above the other ; each chain being formed of round rods, 15 feet long, and 2 inches in dianieter. The suspension-rods are round, an inch in diameter, and are attached alter nately to each of the three tiers of chains. In 1821 Brown commenced the Trinity -sus pension-pier at Newhaven, near Edinburgh, which consists of three spans of 209 feet each, with 14 feet deflection. In 1818 the Holyhead Road Commissioners applied to Telford for his opinion respecting the erection of an iron suspension-bridge at the Menai. A brief account of this beautiful bridge, and of the yet more extraordinary Britannia Tubular Bridge, recently erected near it by MY. Robert Stephenson, will be found under MEwAi Burnous.
- While the Menai Bridge was in progress Sir S. Brown constructed the suspension-pier at Brighton, 'which consists of four openings of 255 feet each, with a deflection of 18 feet ; and Mr. W. Tierney Clark commenced in 1824 the Hammersmith suspension-bridge, the first erected in the vicinity of London. The central opening of the Hammersmith Bridge has a chord-line of 422 feet, with a deflection of about 30 feet. The width of the bridge is about 30 feet, there being a carriage-way of 20 feet, and two side foot-paths of 5 feet each. There are eight chains, arranged in four double lines, or in tr6 vertical tiers. The Hungerford suspension-bridge, opened April 18th, 1845, is for foot passengers only ; the chains are borne by two towers in the river, 22 feet square and 80 feet high, the height of the roadway above high-water mark being 32 feet. The span of the centre between the two towers is 676 feet 6 inches, of each of the side arches 333 feet. The roadway is supported by single suspension rods 12 feet apart on each side. It was built under the direction of Mr. I. K. Brunel.