MASONRY ARCHES. With the beginning of the Nineteenth Century, the masonry arch, which had up to this time been prominent in the field of bridge construction, encountered a rival in the metal bridge, first in the form of the arch and suspension bridge and later in the form where girders were employed. The close of this cen tury saw the metal bridge paramount over the masonry arch in all respects, except when judged from the standpoint of beauty and dura bility. These points of superiority, however, have maintained, and probably will continue to maintain, the masonry arch prominent among the bridge types of the engineer. The number and variety of stone-arch bridges built during the Nineteenth Century preclude a mention of arches, the centre one of which is 76 feet, and each sne•eeding one on each side four feet shorter than the preceding, except in the ease of the two end spans, which are 25 feet. The Winston Bridge over the river Tees, built in 176•. is notable for its span of 108 feet 9 inches. The Kelso Bridge over the river Tweed was com pleted in 1799, and consists of live arched spans of 7• feet each. The Blois Bridge over the river Loire was begun in 1720, and consists of eleven elliptical arches from 54 feet 9 inches to 86 feet 4 inches span. This was the first bridge built after the establishment of the Ports et in France. The Trilport Bridge over the Alaine was finished in 1760, and consisted of a middle arch of Si feet and two side arches of 76 feet 1) inches, built on a skew, the axes of the arches making an angle of 72 with the axis of the bridge. The bridge of Tours on the Loire, begun in 1755, is one of the longest stone-arched bridges in France, consisting of fifteen elliptical arehes of 80 feet span separated by piers 16 feet thick. The bridge of Neuilly, on the Seine, was begun in 1768 and finished in 1774, and consists of five elliptical arches of 125 feet span The bridge of Gignac, on the Wrault, was fin ished in 1793: it consists of two semicircular arctic's of 83 feet span and an elliptical centre arch of 160 feet 9 inches span. lu some respects. the most notable stone-arch bridge of the Eighteenth more than a few representative examples. In 1832 the tIrosvenor Bridge over the river Dee at Chester, England. was completed with a single arch span of 200 feet. The Trezzo Bridge. con structed over the Adda, in Italy, in I380, and destroyed in 1416, had a single arch span sup posed to have been 251 feet, but, with this possi ble exception, the Grosvenor Bridge was at the time of its construction the largest stone-a EA span ever built. In 1857-64 the construction of
the Cabin John Arch near Washington, D. C., with a span of 2•0 feet, transferred the posses sion of the longest stone arch in the world to .America, but as the Cabin John Arch was built to carry an aqueduct, the Grosvenor Bridge re mained the largest span of masonry arch bridge for transportation purposes until 188s. In 1901 there was completed at Luxemburg the largest stone arch; it has a span of 277 feet, and is 137.76 feet above the brook which it bridges. The accompanying table gives the main dimen sions of a number of the leading stone-arch bridges of the world. Structurally, the stone arch bridge of the Nineteenth Century cannot be said to show much improvement over that of pre ceding times, brit the advance in the seienee of statics gave the Nineteenth Century engineer a better theoretieal knowledge of such struetures than was enjoyed by his predecessors. Tin' dis tinctive development of the Nineteenth Century in masonry arch-bridge construction has been the concrete arch with a metal skeleton and arches with hinges in the ring. Concrete, in which a skeleton of metal rods, beams, or netting is im bedded, is one of the systems of arch construction which has gained prominence in recent years. one of the longest structures of this type so far built is the Topeka (Kansas) Bridge, consisting of live 125-feet spans, two 110-feet spans, and two :173 -feet spans. Each arch is of concrete, in which are imbedded twelve lattice girders of steel, spaced three feet apart and bent to the curve of the arch. Numerous other spans of this and other systems of concrete metal•construction have been built in Europe and America. Con crete arches without metal skeletons are less commonly used. Perhaps the most notable use of the plain concrete arch so far recorded was in the extension of the West highland Railroad of Scotland in 1897-98. The longest single span employed was 127 feet, but most of the arches used were of 30 feet and 50 feet span: the larg est structure had twenty-one 50-feet semicircular arch spans, and a total length of 1248 feet. Hinged arches of concrete have been built in considerable numbers in Europe. The hinges are sometimes true hinges of metal or stone placed this type, see Eneyelopffdia of Civil Engineering (London, 1847) , by Edward Cresy, and the vol umes of A ?males des fonts et Chausy'es (Paris, 18:31, current) ; Proceedings, Institution of Civil Engineers (London, 1838, current) ; and Engi neering News.