The New Student's Reference Work/Bridge, Cantilever

Bridge, Cantilever. The first modern cantilever bridge was built in 1882 across Niagara, although its principle had been approached in one or two earlier bridges. The advantage of the cantilever bridge is partly in its erection and partly in its long spans. It is the only bridge that can compete with the suspension for long spans. The principle of the cantilever can be understood from the drawing. A and B are two towers, C and D is a truss anchored at C, resting on tower A and projecting over the river. EBF is a similar truss on opposite side. DE is a simple truss supported at D and E, so as to transmit only vertical loads. A load on D tends to lift C, but does not effect EBF. A load on DE is divided between C and D and EBF.

CANTILEVER BRIDGE

The Forth Bridge in Scotland, one of the most notable bridges in the world, is a cantilever bridge. It has a total length of 8,295 feet, and has two main spans each 1,710 feet long. The largest cantilever structure in the world is the bridge over East River, at New York, known as Blackwell's Island Bridge, built at a cost of nearly $25,000,000. It is double decked, 8,449 feet in length. The length of the main span is 1,182 feet between the towers. On the lower deck, projecting beyond the trusses, is a roadway wide enough for four three-horse teams to pass abreast. On each side of and apart from this roadway are two trolley tracks. In the middle of the upper deck, between the trusses, there are two elevated railroad tracks and two promenades, each eleven feet wide.