Page:Collier's New Encyclopedia v. 02.djvu/203

LEFT BBIDGE 173 BRIDGE Queensferry. At this place, the estuary of the Forth is divided by the island of Inchgarvie into two channels, whose depth, as much as 200 feet, precluded the construction of intermediate piers. Hence, two large spans of 1,700 feet each were adopted. Between these, the central pier is founded on the island midway across, and is known as Inch- garvie pier. There are two other main piers, shore piers, known respectively as the Fife pier and the Queensferry nier. Of these three piers respectively three double lattice work cantilevers like scalebeams, 1,360 feet, or a quarter of a mile in length, are poised in line, reach- ing toward each other, and connected at their extremities by ordinary girders 350 feet long, by which the two main spans are completed. The bridge con- sists of two main spans of 1,700 feet, or nearly one-third of a mile each; two of 675 feet each, being the shore ends of the outer cantilevers; and 15 spans of spans with fixed continuous spans con- necting them. The Queensboro bridge is of the cantilever type. The Quebec bridge, 640 feet long, which fell while in course of construction in 1907, and again in 1917, was completed in the latter year. The Spokane bridge over the Willamette river has a draw span of 521 feet, the largest in the world (1920). The Quebec cantilever-truss bridge (1916) has a span of 1,800 feet. Other notable cantilever bridges are those across the Colorado river, at Red Rock, Cal., and across the Mississippi river, at Memphis, Tenn. Arch Bridges. — Bridges in the shape of arches are often built in places where a more artistic structure than a truss is desired. The High bridge and Wash- ington bridge across the Harlem river in New York City are examples of this style of bridge. The High bridge was built to carry the Croton aqueduct across the Harlem river. It consists of 13 CANTILEVER BRIDGE 168 feet each. The total length of the viaduct, including piers, is 8,296 feet, or a little over 1^4 miles, of which almost exactly one mile is covered by the great cantilevers. The clear headway under the center of the bridge is 152 feet at highwater, and the highest part of the bridge is 361 feet above the same level. Between the two main girders a double line of railway is carried on an internal viaduct supported by trestles and cross girders. The whole of the metal work of the superstructure is of Siemens steel. The way consists of heavy bridge rails laid on longitudinal sleepers bedded in four steel troughs, into which the wheels will drop in case of derailment, tvhen they will run on the sleepers. In the piers there are about 120,000 cubic yards of masonry, and in the su- perstructure 44,500 tons of steel. There are several of these bridges in the United States, the first of any size being the Niagara cantilever, built in 1883. Its total length is 910 feet, and it is 295 feet above the surface of the river, with steel towers 130 feet high. The Hudson river bridge at Pough- keepsie, built in 1889, has a length of 6,767 feet and is built in five spans; the first, third and fifth being true cantilever 12 — Vol granite arches, the highest one being 116 feet above the river. The bridge, cross- ing the river and valley, is 1,460 feet long. The Washington bridge is situated a short distance N. of the High bridge and consists of nine arches, three of granite on the E. side, four of granite on the W., and two central steel spans connecting them. The entire length of the bridge is 2,300 feet, and width, 80 feet; the central spans being each 510 feet long and 135 feet above high water. Another noted arch bridge is located at St. Louis, Mo. It has two spans of 497 feet and one of 515, with a total length, including abutments of 1,700 feet. It is a two story affair with a double rail- road track below and a roadway above. The Hell Gate bridge over the East River in New York City is 1,000 feet in length, and is the largest arch bridge yet constructed. It was completed in 1916. American Qnadrangxdar Girder Bridges. — One of the best examples of American long-span iron-bridge con- struction is the bridge across the Ken- tucky river on the Cincinnati Southern railroad, noteworthy for its economical design and comparatively light weight. The iron work of the bridge is 1,138 feet II— Cyft