Bridge
a structure consisting of an arch or series of arches supporting a roadway above it, designed to unite two banks of a river or the two sides of an open space. A bridge is generally made of wood, iron, stone, steel, or of brick.
The extreme supports of the arches at the two ends are called butments, or abutments; the solid parts between the arches, piers, and the fences on the sides of the road or pathway, parapets.
Bridges are now of many kinds, the most usual varieties being the following:
Suspension Bridges. - These bridges are such in which the roadway is suspended from chains, links, cables or ropes, passing over piers or towers, fixed or anchored at their extremities.
Another line of evolution had its origin in the principle of suspension. In the typical modern suspension bridge, when the weight of the roadway is known by the stress on the suspending links, the and Long Island City, is 7,144 feet long and 90 feet wide.
Cantilever Bridges. A cantilever is a bracket. It is a structure overhung from a fixed base. The bridge across the river Forth on the North British railway system is one of the largest and most magnificent bridges in the world. The site of the bridge is at BRIDGE Queensferry. At this place, the estuary of the Forth is divided by the island of into two channels, whose depth, as much as 200 feet, precluded the construction of intermediate piers.
Hence, two large spans of 1,700 feet each were adopted. Between these, the central pier is founded on the island midway across, and is known as Inchgarvie pier.
There are two other main piers, shore piers, known respectively as the Fife pier and the Queensferry pier.
Of these three piers respectively three double lattice work cantilevers like , 1,360 feet, or a quarter of a mile in length, are poised in line, reaching toward each other, and connected at their extremities by ordinary girders 350 feet long, by which the two main spans are completed. The bridge consists of two main span of 1,700 feet, or nearly one -third of a mile each; two of 675 feet each, being the shore ends of the outer cantilevers; and 15 spans of BRIDGE spans with fixed continuous spans connecting them . The Queensboro bridge is of the cantilever type. The Quebec bridge, 640 feet long, which fell while in course of construction in 1907, and again in 1917, was completed in the latter year. the Willamette river has a draw span of The Spokane bridge over 521 feet, the largest in the world (1920).
The (1916) has a span of 1,800 feet. Other Quebec cantilever-truss bridge notable cantilever bridges are across the Colorado river, at Red Rock, those Cal., and across the Mississippi river, at Memphis, Tenn. of arches are often built in places where Arch Bridge-Bridges in the shape a more artistic structure than a truss is desired . The High bridge and Washington bridge across the Harlem river in New York City are examples of this style of bridge. The High bridge was built to carry the Croton aqueduct across river. It consists of 13 CANTILEVER BRIDGE 168 feet each. The total length of the viaduct, including piers, is 8,296 feet, or a little over 1½ miles, of which almost exactly one mile is covered by the great cantilevers . The clear headway under the center of the bridge is 152 feet at , and the highest part of the bridge is 361 feet above the same level.
Between the two main girders a double line of railway is carried on an internal viaduct supported by trestles and cross girders.
The whole of the metal work of the superstructure is of Siemens steel.
The way consists of heavy bridge rails laid on longitudinal sleepers bedded in four steel troughs, into which the wheels will drop in case of derailment, when they will run on the sleepers.
In the piers there are about 120,000 cubic yards of masonry, and in the su- 44,500 tons of steel.
There are several of these bridges in the United States, the first of any size being the Niagara cantilever, built in 1883. Its total length is 910 feet, and it is 295 feet above the surface of the river, with steel towers 130 feet high.
The Hudson river bridge at Poughbuilt in 1889, has a length of 6,767 feet and is built in five spans; the first, third and fifth being true cantilever 12-Vol. granite arches, the highest one being 116 feet above the river. The bridge, crossing the river and valley, is 1,460 feet long. The Washington bridge is situated a short distance N. of the High bridge and consists of nine a granite on the E. side, four of granite arches , three of on the W., and two central steel spans connecting them. The entire length of the bridge is 2,300 feet, and width, 80 feet; the central spans being each 510 and 135 feet above high water.
Another noted arch bridge is located at St.
Louis, Mo. It has two spans of 497 feet and one of 515, with a total length, including abutments of 1,700 feet. It is a two story affair with a double rail- The Hell Gate bridge over the East road track below and a roadway above.
River in New York City is 1,000 feet yet constructed. It was completed in in length , and is the largest arch bridge 1916.
Bridges. - One of the best examples of American Quadrangular Girder American longspan iron-bridge construction is the bridge across the Kentucky river on the Cincinnati Southern railroad, noteworthy for its economical design and comparatively light weight.
The iron work of the bridge is 1,138 feet II-Cyc BRIDGE in length, and it consists of three spans of 375 feet each. It crosses a limestone canon at a height of 280 feet above the bed of the stream. The piers are of stone to a height of 60 feet, to clear the highest recorded floods; and they are about 34 feet thick at the flood level.
Above the stonework the piers are of iron. The truss or girder is rectangular in section, 37½ feet high, 18 feet wide, consisting of top and bottom pairs of PARKER TRUSS BALTIMORE TRUSS PENNSYLVANIA TRUSS WARREN TRUSS XXXXXX XXXXXX HOWE TRUSS LENTICULAR TRUSS "K" TRUSS TYPES OF BRIDGE TRUSSES booms, forming the corners, united by panels or frames at intervals of 18% feet longitudinally, stiffened and bound with diagonal tie rods. The booms each consist of flat plates placed vertically, riveted together. The piers consist of hollow pillars of plate iron riveted together in box form. The diagonal rods are pin connected, that is to say, they are connected to the framework with cylindrical pins, a form of connection much practiced in the United States.
The bridge was completed in February, Lattice Girder Bridges. - The iron BRIDGE lattice bridge, so called from having sides constructed with cross bars, like lattice work, is the natural outcome of the tubular bridge for long spans, developing equal strength with considerable economy of material and labor. Lattice girders are now almost universally adopted for iron bridges for long spans.
Movable Bridges. - Movable bridges are usually required in the neighborhood of rivers, docks, wharves, canals, and like situations for the passage sage of ships and boats. They are variously designed and adapted to particular situations, and may be classified as (1) bascules or drawbridges, (2) swing bridges, (3) traversing bridges, (4) lift bridges, (5) pontoon bridges.
Bascules or Drawbridges. The bascule bridge is such as is raised by turning, in one piece or in two pieces, round one or two horizontal axes or hinges.
For large dimensions it is convenient to construct the bridge in two halves, lifting from each side, and abutting together to the middle. A bridge of this sort has been built across the Thames at London and another for elevated railroad use across the Chicago canal. They are now comparatively common. The largest one of the type was completed over the Chicago river in 1919.
Swing Bridges. --Swing bridges are by far the most commonly employed of movable bridges. The large rivers to be crossed in the United States have demanded swing bridges of great span, with excellent contrivances for minimizing friction and insuring steadiness when closed. The swing bridge over the Raritan, in New Jersey, allows two free passages, each 216 feet wide. The Kansas City bridge crosses two passages, each 160 feet wide. The total moving weight is 303 tons. The bridge is opened by steam power in about one and a half minutes, or by manual power in two minutes.
Traversing Bridges. - Movable bridges, sometimes called telescope bridges, capable of being rolled horizontally backward, or in an oblique direction, are occasionally employed. The bridge across the Arun, near Arundel, on the South Coast railway, is 144 feet long. It is traversed on wheels, and acts as a sliding cantilever, the overhanging portion resting on the opposite abutment when in place.
Lift Bridges. - A notable example is the one erected over the Surrey canal, which is lifted by the four corners; another over the Royal canal, Dublin.
Pontoon Bridges. - Bridges of boats are made of boats laid over with planks, fastened across the stream by means of anchors or stakes. The bridge at Rouen BRIDGE is 300 yards long, paved with stone for the passage of carriages and horses. The so-called flying bridge is rather a ferry than a bridge of boats.
The longest floating bridge in the world, probably, is the pontoon bridge across the river Hooghly, at Calcutta, BRIDGE ends. They are each of the great length of 160 feet, made of such considerable length in order to obviate pitching motion in rough weather. The roadway platform is of 3-inch planks of teakwood from Burma, forming a roadway 48 feet wide, with a footpath at each side 7 feet HELL GATE BRIDGE OVER EAST RIVER, NEW YORK designed and constructed by Sir Bradford Leslie. The bridge is 1,530 feet long between the abutments, and is carried on 14 pairs of pontoons, which are held in position by means of chain cables , 14 inches thick, and anchors weighing three tons each, laid on the up stream and down stream sides, 900 feet asunder. By wide. An opening 200 feet wide, for the passage of ships, is made by removing , when occasion requires, four of the pontoons with their superstructure, and and sheering them clear of the opening . The floating bridge is connected with the shore at each end by adjusting ways hinged to the shore.
ROLLING LIFT BRIDGE their great length, the cables afford the necessary spring to allow for the ordinary rise and fall of the river, the stress on each cable varying from 5 tons to 25 tons, according to the stage of the weather and of the tide, the maximum velocity of which is 6 miles an hour. The pontoons are rectangular iron boxes, having rounded bilges and wedge-shaped Military Bridges are temporary constructions to facilitate the passage of rivers by troops, to restore a broken arch, or cross a chasm of no very great width .
Those over a river are either floating or fixed. The former are made of pontoons , boats, casks, rafts of timber, or anything that will give sufficient buoyancy; and the latter of piles, trestles, or other timber BRIDGE work. Spars, ropes, and planks are used in a variety of ways for spanning narrow chasms. The pontoon bridge is the only one which is carried with an army.
Heavy guns are better warped across on specially constructed rafts. A flying bridge is a boat or raft anchored by a long cable up stream, and carried across by the action of the current acting obliquely against its side, which should be kept at about an angle of 55° with the current.
Of the rock formations called natural bridges, the most remarkable is the DOC BRIDGE countries of imperfect civilization even yet they are few.
Following is a list of the notable bridges of the world:
Pons Sublicus, across the Tiber at Rome, defended 507 в. c., by Horatius Cocles.
Cæsar's bridge across the Rhine, a wooden trestle-work, built 55 в. c.
Trajan's magnificent bridge over the Danube, 4,770 feet in length, built A. D. 115.
London bridge. One existed at the end of the 10th century; one built of wood, Car LARIMER BRIDGE, PITTSBURGH, PA.-A CONCRETE ARCH natural bridge over Cedar Creek, in Virginia, 125 miles W. of Richmond. The mass of siliceous limestone through which the little river passes is presumably all that remains of a once extensive stratum.
The cavern or arch is 200 feet high and 60 feet wide. The solid rock walls are nearly perpendicular, and the crown of the arch is 40 feet thick.
History of Bridges. - Bridges seem to have existed in China from a period of considerable antiquity. The word bridge does not occur in the Authorized Version of the Bible. Temporary bridges, for military purposes, were constructed before permanent structures for the convenience of the inhabitants were erected. The former were often of boats. Thus, Cyrus constructed such bridges about 536 B. C., Darius Hystaspes about 490, and Xerxes about 480 B. C.
Bridges of stone or brick seem to have been first used by the Romans; there were none erected in Greece till after the Roman conquest. The first Roman bridge is said to have been one spanning the Tiber, between the Janiculum and the Aventine mountain, built by or under Ancus Martius. Now they are universal in properly civilized countries, though in 1014; a stone bridge, by Peter of Colechurch, begun 1176, was finished 1209. The new London bridge is constructed of granite, from the designs of L.
Rennie; it was commenced in 1824 and completed in about seven years, at a cost of $7,290,000.
The bridge at Burton, over the Trent, was formerly the longest bridge in England, being 1,545 feet. It is now partly removed. Built in the 12th century.
The Bridge of the Holy Trinity, at Florence, Italy, was built in 1569. It is 322 feet long, constructed of white marble, and stands unrivaled as a work of art. signs, The Rialto, at Venice, is said to have been built from the designs of Michael Angelo. It is a single marble arch, 98½ feet long, and was completed in 1591.
The Bridge of Sighs, at Venice, over which condemned prisoners were transported from the Hall of Judgment to the place of execution, was built in 1589.
Brooklyn Bridge was commenced, under the direction of John A. Roebling, in 1870, and completed in about 13 years.
Coalbrookdale bridge, England, was the first cast-iron bridge. It was built over the Severn in 1779.
BRIDGE High bridge, New York, by which the Croton aqueduct is carried across Harlem river, is of granite throughout. Victoria bridge, which spans the St.
Lawrence at Montreal, Canada. It is tubular and 9,194 feet, or nearly 2 miles, long. The massive tube through which the railway track is laid is 22 feet high and 16 feet wide. It was formally opened in 1860.
BRIDGE as war memorials. A notable one is the State Soldiers' and Sailors' memorial bridge at Harrisburg, Pa., built at a cost of over $2,000,000, and completed in 1919.
Besides the bridges here enumerated, there are many other notable specimens of bridge architecture in this country.