Some of the other handsome and important structures of the metal hinged-arch type well worthy of mention are the following: The Washington Bridge over the Harlem River, at New York, completed in 1889, which consists of two magnificent arches, each 510 feet in span, flanked by four masonry arches at one end, and three at the other, each 50 feet in span; the Detroit-Superior Bridge, a three-hinge steel arch truss of 591 feet span, with a double deck for pedestrians, vehicles and electric cars; the Old Trails Arch Bridge over the Colorado River, below Needles, Cal., a three-arch span of 592 feet; the German steel-arch bridges across the Rhine at Bonn and Diisseldorf, the former with a central arch of 614 feet span, and two side deck arches each 307 feet in span, and the latter with two central arches each 595 feet in span; the Pia Maria Bridge over•the Douro at Oporto, Portugal, consisting of a main steel arch of crescent design, 525 feet in span with a rise of 123 feet; and the steel arch on Garabit Viaduct over the Truzire, in central France, which has a span of 540 feet with a rise of 170 feet, and the deck 406 feet above the water.
As the tensile strength of wrought iron and steel was greatly increased by improved proc esses of manufacture, great feats of bridge construction were dared by the bridge engineers, and various types of suspension and cantilever bridges, especially suitable for very long spans, were designed and successfully erected. The first wire suspension bridge in any country was the Schuylkill River Bridge at Philadelphia. built in 1816. It had a span of 408 feet and was but 18 inches wide. It was supported by cables of six 3i-inch wires. But even the more important wire cable and chain structures of the early 19th century, such as the bridge across the Menai Strait, between the Island of Anglesey and Carnarvonshire, in Wales, com pleted in 1826, with a span of 580 feet, and Fribourg Bridge. in Switzerland, built in 1834, with a span of 870 feet, were completely over shadowed by the works of the American en gineers during the period dating from 1848 onward. Of these magnificent structures, the most notable are the following: The bridge at Wheeling, W. Va., erected by Charles Ellet, in 1848, with a suspension span of 1,010 feet; the Niagara Bridge, built by John A. Roebling, in 1855, with a clear span of 825 feet, and particularly distinguished as the first railway suspension in the world ;*the Cincinnati and Covington Bridge, built by the same en gineer, in 1867, with a clear span of 1,057 feet, and a total length of 1,692 feet; and the last creation of the same engineer, the first New York and Brooklyn Suspension Bridge, across the East River, which was completed in 1883. This bridge connects Park Row, Manhattan, with Sands and Washington streets, Brooklyn. It was begun in 1870, and completed in 1883, at a cost of $9,000,000. It has been altered, re
paired and extended so that its total cost in 1912 was about $22,400,000, or more than any other bridge in the world. The original struc ture consisted of a main suspension span of 1,595% feet, and two shore spans of 930 feet each. With the approaches it had a total length of 5,989 feet, but these approaches have been extended so that the total length of the bridge with extensions is now 7,580 feet. The four steel wire cables are each 1534 inches in diameter, and support the roadway and the stiffening trusses at a height of 135 feet above high-water level, at the centre of the span. The combined supporting strength of the cables is 48,000 tons. The cables are carried over saddles at the tops of two stone towers, each 278 feet above high water, and anchored at each end in solid cubical structures of stone masonry 119x132 feet, which rise to 90 feet above high water. The width of the bridge is 85 feet, and there are four tracks, two of which carry the cars of the elevated road, and two for surface trolley cars. There are also two driveways and a footway. The traffic on this bridge is greater than on any other. In 1913 the average daily traffic was 7,352 elevated railway cars, 7,725 surface cars and 4,214 vehicles.
The Williamsburg Bridge is noteworthy as being the first great suspension bridge to em ploy steel instead of masonry towers, and as having the longest suspended span built up to 1912. It connects Delancey street, New York, with South Fifth and Sixth streets, Brooklyn, and was completed in 1904, requiring eight years for construction. It has a span of 1,600 feet and a total length of 7,308 feet. Four steel wire cables, each 18% inches in diameter, swung from two steel towers, each 333 feet above high water, support the roadway platform and the stiffening trusses at a clear headway of 140 feet above high water level, at the centre of the span. The width of this bridge is 118 feet and the roadways are on three levels, so that it has greater carrying capacity than the Brooklyn Bridge, though the traffic is less. On the lower level are four tracks; on the second, two vehicle ways and two footways; on the third, tracks for elevated cars. The tower foundations were sunk 66 feet on the New York side and 107 feet on the Brooklyn side, at the lowest points, so that the extreme height of structural work is 440 feet. There are 17,403 miles of wire in the cables, and the four cables with suspenders weigh 4,900 tons. The weight of steel and iron in the main bridge is 23,R00 tons, and in the approaches 16,600. Its carrying capacity is 38,770 tons. The anchorages meas ure 149 x 128% feet at the top and contain 112, 800 cubic yards of masonry. The cost, exclu sive of land, was $14,000,000.