BRIDGE. 48-t BRIDGE. five. In 1873 the arcli bridge over the Mississippi at !>aint Louis, Mo., was completed with a centre span of 520 feet and two side spans of 502 feet; each span consisted of four parallel cast-steel arch ribs, and the bridge carried two railway- tracks and a highway. The cost of the Saint Louis Bridge was about .iio.JiOOjOOO. No other instance of a bridge of important size being built of cast-steel arches was recorded until IS'J'J, when the Alexander 111. Bridge, across the Seine at Paris, was completed with a single span of 352.0 feet, the arch ribs being made u|) of wedge-like cast-steel sections bolted together. Unlike the Saint L<mis Bridge, which was built without hinges, the Alexander III. arch had liingcs at the crowTi and abutments. The longest span arch bridge of wrought steel in the world is the high- way and foot bridge built across the gorge of the Niagara River, just below the Falls at Niagara, in ISnS-iW. with a single span of 840 feet. In 1897, a steel-arch railway bridge was built across the same stream about .a mile farther down- stream, with a span of 550 feet. Both of these structures were erected without false works to support the metal during erection : each half arch was built out from the shore, member by mem- ber, and held back by strong anchors to the shore until the ends met at mid-stream. One IS not a single steel-arch span of notable dimen- sions. For the discussion of the theory of the metal arch, see a Treatise on Arches, by Prof. M. A. Howe (New York, 1807), and for descriptions of notable structures of this type, see the vol- umes of Trunsiicliuiis Ai/ieriean Society of Civil Ivnyineers (New York, 1808, current) ; Annates tics Fonts et Chaussccs (Paris, 1831, current); and the American and European engineering journals. SUSPENSION BRIDGES. In their crudest form of two parallel cables carrying a door directly on the cables, suspen- sion bridges have doubtless been used since very early times. Such bridges, with the cables com- posed of vegetable fibre and creepers, have been found to be used by the aborigines of numy countries. It is probable that the Chinese sus- I)ension bridges built during the Sixteenth Cen- tury were of this construction, and it is certain that it was the construction of the few European suspension bridges which were built previous to 1800. The first suspension bridge of the modern form, having a platform or a roadway suspended from the cables, is considered to have been erect- ed by .Joseph Finley, near Greensburg, Pa., in Table of Dimensions of Notable Metal-Arch Bridoer Country No. of Ribs Niagara (N. Y.) Viaur River Bonn DUsseldorf .*. Oporto Miingsten Niagara (N. Y.) Oarabit Leveneau Oporto Saint Louis (Mo.) Grlinentii.ll WaHhinpton (New York Cit.v) . Souttiwarlv ArVearnif)ntii Saint Louis RoclJCreeli (Wasli.) U. S. A. France Germany Portugal Germany tl. S. A. France Germany Portugal U. S, A. Germany U. S. A. England France U. S. A. Class of Bridge Highway Railway Highwa,T H'w'y&Ry. Railway Hw'y&Ry. Highway Date Built 1898-9 1898-9 1898 1896-8 1886 18%-7 1897 1884 1894 1877 1873 1892 1886-9 1819 1793 1860-62 1868 Kind of Metal Steel Wrt. Iron Mai. Iron Cast Steel Wrt. Iron Steel Cast Iron Longest Span, feet 840 721.6 614 694.5 666 557.6 560 641.3 636 624.6 520 513.6 608.8 240 236 210 200 No. of Hinges of the handsomest steel-arch structures in the ■world is the Washington Bridge at New Y'ork City, completed in 1889 at a cost of .$2,8.50,000. This l)ridge has two metal arches of 510 feet span each. Hanked at each end by masonry arches of 50 feet span, four at one end and three at the other. The arches of the Washington Bridge and the two Niagara bridges have hinges at the abutments only. Turning to Eurojie, mention nuiy l>e made of the Miingsten Bridge across the river Wupper on the line of the Solingen-Rem- scheid Railway. This bridge has a centre arch span of 590 feet, without hinges, and steel tres- tle approaches at each end. It was completed in 1897. Two notable German steel-arch bridges of recent construction are the Bonn Bridge and Dlisseldorf Bridge over the Khine at the cities named. The Bonn Bridge has a centre arch of <il4 feet span and two side arches of 307 feet span, and the Diissehlorf Bridge has two spans of 595 feet each. In France the Viaur Viaduct, with a single arch span of 721.0 feel. biilt in 1808-99, holds the record for the second longest steel-arch span in the world. In Kngland tlicre 1801. The span was short (only 70 feet), but it consisted of two chain cables passing over shore towers to inshore anchorages, and had a platform suspended from them. Several other bridges of the same general construction were built by Finley and others in succeeding years n]) to 181(1, when a foot bridge of 408 feet span was built over the Schuylkill River at Phila- delphia, whose cables were made of wire. In 1819 the first suspension bridge in England built with a suspended jjlatform was erected over the river Tweed. In 1820 the famous chain suspen- sion bridge across the Jlenai Strait was com- pleted, with a total length of 1710 feet and a suspension span of 580 feet. In Continental Europe suspension-bridge construction was be- gun about 1820, and in 1834 Continental engi- neers established the world's record in long suspension spans by building the Fribourg Bridge in Switzerland, with a span of 870 feet. In 1848 the United States again took the lead through the erection by Charles Ellet of a sus- pension span of 1010 feet at Wheeling, W. Va. These early susjjension bridges were flexible
