The Erie Railway completed in 1910 a steel viaduct in Jersey City, N. J., having a length of 1,776 feet, and leading up to a cut in Bergen Hill. This involved bridgework of structural steel, resting on concrete. Owing to the soft nature of the ground, which was largely wet sand, it was necessary to sink many concrete caissons, and where the sand was more solid to use concrete piles.
Recent Foreign The Que bec Bridge a cantilever truss, having the longest span (1,800 feet) of any bridge to date (1916). surpasses the Forth Bridge (Scotland) by 90 feet, and the Williamsburg Bridge by 200 feet. It was designed to carry two railroad tracks loaded with the heaviest modern traffic and two footways. The live load was figured at 5,000 pounds per lineal foot, with two E-60 locomo tives. The wind pressure is figured at 30 pounds per square foot of both trusses and 300 pounds per square foot of trains. The main posts of the cantilevers over the piers are of four separate columns latticed together, 9 feet by 10 feet each, standing on a shoe 19 feet high and 22 feet by 26 feet at its base and weighing 400 tons. The maximum cross sec tion of the posts is 1,903 square inches, and they weigh 1,500 tons each. The members next to the posts are 7 feet 2 inches deep by 10 feet 4 inches wide, and have a cross section of 1,902 square inches. They are composed of four webs 7 feet deep, each web being of four plates riveted together, having a total thickness of 3y, inches. The suspended span, 640 feet long and 88 feet wide, was assembled on a pile trestle nearby and six scows floated under it at the panel points and sunk on prepared foundations. Cross girders and bracing were built up on the scows, at low water the scows were drained, and at high water the span floated free of the trestle. It was lifted to its place from the river by eight 1,000-ton hydraulic jacks, two at each of the corners of the cantilever arms. There has not been any such remarkable bridge build ing in the Old World. Two new bridges were completed over the Rhine at Cologne in 1908, one having 492 feet of span and the other 550 feet. The Risorgimento Bridge, across the Tiber at Rome, was completed in 1911. It has a span of 328 feet, and is chiefly noteworthy because of its historic site, and from the fact that the false work on which the arch rested during construction was built of steel and con crete, instead of wood.
The Swiss Sitter River Viaduct, which was completed in 1911, is only 400 feet long, but is notable because it crosses a gorge at a height of 1,130 feet. At•Auckland, New Zealand, was completed in 1910, the largest concrete arch in that part of the world, having a span of 320 feet, the minor spans giving the bridge a total length of 960 feet. In Africa the Sudan Rail way has built a bridge over the Blue Nile at Khartum, which was completed in 1909, and which rests on 20 steel cylinders, each 16 feet in diameter, and carried down as far as 60 feet below low water. The seven largest spans of this interesting bridge are each feet. In
Tonkin, Indo-China, French interests have built a bridge over the Red River, a cantilever, of 19 spans, having a total length of 5,544 feet. The longest span is 429 feet. The Yunnan Sys tem Railway will use the bridge.
The suspension principle has been far more extensively employed in America, and especially in the United States, than in foreign countries. Some of the European suspension bridges, how ever, are of great beauty of design, such as the structure across the Danube at Buda-Pesth in Austria-Hungary, which is considered to be the handsomest bridge in the world, but they are entirely outclassed in magnitude by the almost marvelous creations of American engineering genius already described.
Bridges built on the cantilever or balanced `span principle rank with those of the suspension and girder-and-arch type for the purpose of spanning great intervals.
In order to trace the evolution of the canti lever-bridge from the girder, and to understand its relation to the truss, a brief mention of the tubular bridges which were originated by Robert Stevenson, engineer of the Chester and Holy head Railway, England, to carry that railway 'across the Menai Strait is necessary.
A 'series of experiments conducted by Ste venson, in conjunction with Fairbairn, demon strated that a rectangular tube with a cellular top and bottom gave a girder in which the greatest strength was derived from the least amount of material. The result was the con struction of the Conway and Britannia bridges, the former across the Conway River and the latter across the Menai Strait, in 1846 and 1847, respectively. The Conway tube consisted of a single span of 400 feet, and the Britannia of four spans, two of 460 feet each, and two of 230 feet each in the clear. The example set by Stevenson was followed in a few other cases, the most important of which was the Victoria Bridge across the Saint Lawrence, near Montreal, Canada, built in 1854. It con sisted of 24 spans ranging in length from 242 to 247 feet each, and one span of 330 feet. It had a total length of 9,144 feet, or nearly one and three-quarter miles, and required about 9,000 tons of iron for the construction of the tubes. It was replaced in 1898-99' by a pin-connected truss bridge of 24 spans of 254 feet each, and one span of 348 feet, which repre sented a total weight of 20,000 tons of steel, but which was capable of sustaining a load five times greater. The Victoria Bridge was the last important structure of this type, which dis appeared from engineering practice when the special conditions which developed it ceased to exist; but it led the way to the plate girder bridges. It taught the engineer to cut away all the useless material in the plans of his struc tures and retain only the effective working skeleton, and thus inaugurated a truly scientific method of metal construction, by which the weight of the structure was greatly reduced, and consequently its cost of construction.