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338 BRIDGES [EXAMPLES iron, to which must be added 50 tons for the platform, making the total weight of each bridge 294 tons 10 cwt. The cost, exclusive of the masonry of the abutments, and of the permanent rails, but inclusive of the staging for fixing and the expense of testing, was .11,003. Crumlin The Crumlin Viaduct, begun in 1853, and completed in Viaduct. 1857 (fig 4, Plate XIX.), is a fine example of the Warren girder j it was erected on the Taff Vale Extension Railway under Messrs Liddell and Gordon as engineers, by Mr T. W. Kennard as contractor. The following description is compiled from that given in Mr Humber s work: The length of the bridge is 1800 feet, divided into two parts, one consisting of seven spans of 100 feet, and the other of three similar spans. The greatest height of the road-way r FIG. 129. Common type of Wrought Iron Girder. above the surface of the water is not less than 200 feet. The piers are formed of cast-iron hollow columns, each 17 feet long and 1 foot in diameter ; the thickness of the metal varies from 1 inch to |-th inch ; these columns are arranged in tiers, each containing fourteen columns, the distance between which at the base of the pier measures 1 3 feet 6 inches, excepting between the centre rows, where it measures 6 feet throughout the height. The wrought iron girders are 150 feet in length and 14 feet 6 inches deep. Some details of the construction are shown in fig. 128. Fiot. 130. Common type of Cast-Iron 3-irder. Fig. 129 shows a plan and elevation and cross section for half a wrought iron girder of a usual type for small spans. Covering plates are used to connect the main plates of the top and bottom webs, and stiffening angle irons are shown at the sides. Similarly, fig. 130 shows a plan and elevation of a cast- iron girder of a usual type. 80. Niagara Suspension Bridge. Fig. 5, Plate XIX., shows Niagara Suspension Bridge, a structure described as follows in the 8th edition : " It crosses the Niagara River at a height of 245 feet above the water by a single span of 821 feet 4 inches, and forms the connecting link between the American States and Canada. " The superstructure may be best described as a hollow rectangular box, 18 feet deep and 24 feet wide, on the top of which the railway is laid, while the bottom, which is 25 feet wide, forms the roadway for public traffic both these floors are constructed of timber beams ; and each connect ing side consists of a row of double posts or uprights of timber, each pair being 5 feet apart; between them wrought iron diagonal bars are made to pass, extending each way to the fourth pair of posts at an angle of 45 degrees. The upper or railway floor is suspended from two wire cables at intervals of 5 feet, and the lower floor is suspended at similar intervals from two other wire cables which have a deflection of 1 feet more than the upper ones; these cables, four in number, are each 10 inches in diameter, and composed of seven strands, each containing 520 wires, making a total of 3640 wires. One strand forms the axis round which the other six are twisted. Sixty wires are equal to 1 square inch of solid section ; therefore the total area of each cable is 60 "4 square inches, or the total sectional area of iron support ing the structure is 241 6 square inches. " Each cable rests upon a separate saddle, there being two on the top of each of the four towers. The saddles are placed on ten cast-iron rollers, 5 inches diameter and 25 inches long, which bear upon cast-iron plates 8 feet ".quare and 2| inches thick, strengthened by three parallel Janges which form two compartments for the reception of the saddles. " The ends of the cables are attached to cast-iron shoes, in each of which is inserted a wrought iron pin which forms the connection with the anchor chains. These anchor chains are each embedded in a solid shaft of masonry 7 feet by 3 feet, enlarged at the bottom to form a chamber 8 feet square cut in the rock. The shafts are sunk to a depth of 25 feet on the New York side, and 35 feet on the Canada side. " Each anchor chain is composed of nine links, the eight lower links being 7 feet long, and the ninth or uppermost 10 feet long. The lowest link consists of seven wrought

iron bars, 7 inches by 1 4 inches each, and amounting