Arched Bridge

Arched stone bridges built by the Romans are yet standing, and during the Middle Ages many were erected, the longest span being 184 ft. An arch built during the 14th century over the Adda in Italy is said to have IMG:content-0233.jpg:[graphic][merged small][merged small] Chandler's Encyclopedia sive. Concrete has lately been used for arched bridges of small span. Timber arches of framed and jointed pieces were formerly much employed for bridges; some of those in Trajan's bridge, built 105, were 180 ft. in span. Cast-iron bridges were first constructed during the latter part of the 18th century, the longest being the 240 ft. spans at Sunder land and South wark, England. Wrought-iron and steel arches are now extensively used for bridges, the longest being that in the Garabit viaduct in France, whose span is 541 ft. The longest span of the steel arch of the Washington Bridge over the Harlem R., N. Y., is 508 ft., and that of the St. Louis bridge over the Mi i ippi is 515 ft. The figure shows the bridge at Johns town, Pa, which resisted the destructive flood of 1889.