Continuous-truss bridges are comparatively lit tle used. but are far more popular in Europe than in America. A continuous truss, as al ready stated, differs from a simple truss by ex tending continuously over three or more sup ports. Theoretieall•, a continuous-truss bridge requires less material than a bridge with the same number of simple-truss spans; but it has a number of practical disadvantages which make engineers loth to use it. Perhaps the most notable continuous-truss bridge in the world is the Laehine Bridge across the Saint Lawrence River at Montreal, Canada, built in 1887. It consists of two centre through spans of 408 feet (melt and two side spans 269 feet. forming a con tinuous structure over five piers.
Cantilever bridges are, strictly speaking. hinged continuous girders. They were not much used until the last quarter of the Nine teenth Century, when the building of the Ken tucky Viaduct (1S76) and the Niagara Canti lever (1883) demonstrated the practicability of erecting such bridges without the use of sup porting false works. Since these dates nu merous cantilever bridges have been erected in both Europe and America. Briefly defined, a cantilever bridge consists of a continuous-truss span starting from an abutment and extending over and beyond a second support on each side of the stream. The two projecting ends are connected by a truss span suspended from them. The shore ends of the spans are anchored to the abutments. The Niagara Cantilever Bridge, completed in 1883, has a total length between abutments of 910 feet. The projecting arms or cantilevers are each 175 feet, and the truss span which they support is 175 feet long. The Saint
John River (New Brunswick) Cantilever, built in 1895, has a total length of 813 feet and a main span of 477 feet. The Poughkeepsie Bridge. built in 1889, has a total length of 6767 feet, with live river spans, of which the first, third, and fifth arc cantilever spans, and are 548 feet. 546 feet, and 5-18 feet, respectively. The Red Rock Cantilever .Bridge, built in 1890, Red River, Cal., has a total length of 990 feet and a centre span of 660 feet. The Alemphis Bridge, built in 1S9.2 over the Mississippi River, at Memphis, Tenn., has a truss span of 621 feet and two cantilever spans of 790 feet, which are the longest cantilever spans in the United States. The longest cantilever span in Conti nental Europe is the 623-foot span of the Danube Bridge, near Czernavoda, in Rumania. Great Britain has the honor of having at present the longest cantilever span in the world, in the great Forth Bridge across the Firth of Forth, in Scotland. This bridge has two cantilever shore arms of 680 feet, and two main cantilever spans of 1710 feet. It was begun in 1SS3 and was completed in 1890. The Quebec Bridge across the Saint Lawrence River, upon which construction was begun in 1900, has a main can tilever span of 1800 feet. For theoretical dis cussions of girder bridges, see the text-books named at the end of this article; and for de scriptions of many of the prominent structures mentioned, see Transactions American Society of Civil Engineers; T. Cooper, American Railway Bridges; and the volumes of the engineering journals.