Pontoon bridge

“ Sometimes a bridge is made movable by swinging it round on a pivot instead of drawing it up on a hinge or axis; and sometimes, as in the case of a bridge over the Arun for the Brighton and South Coast Railway, it is made to slide on wheels backwards and forwards from the abutment. Floating or pontoon bridges are made by placing planks on pontoons, or boats anchored by cables. The longest in the world is probably at Calcutta, across the Hooghly. It is 1530 feet in length, there being twenty-eight pontoons in pairs. ”

“ Down by the river-bank a large force of engineers were working like mad to throw a pontoon across the swift current. The material had already been brought up—heavy, flat-bottomed boats, carried on wagons drawn by motor-tractors, great beams and planks, boxes of bolts—everything, in a word, needed to build this bridge just here at a point which had no doubt been selected long in advance! The bridge shot out into the river with a speed which seemed to Stewart almost miraculous. ”

“ Fig. 99. The Pontoon Bridge. “Slab” is the lumberman’s name for the outside piece of a log which is sawn off in squaring up the sides. We made a raft of these materials and floated them down the river to Lake Placid. The bridge was made by anchoring the barrels in the channel about eight feet apart, and laying on them the floor beams, which supported a flooring of slabs. The floor beams were narrow planks 1 inch by 4 inches, taken from 102 the bridge wreck, and they were placed on edge to prevent sagging. ”

“ It is loaded so as to draw 10 feet of water, and is capable of storing 4,000 tons of coals. To connect the pontoon with the shore there is an iron bridge, working upon hinges, in two spans of 125 feet each. The connection between the two spans was supported on a timber pier, and was made so as to be movable vertically, and capable of being adjusted by a crab and counterbalance weights. By means of this arrangement a uniform gradient over the whole length of the bridge could be obtained at any time of tide, for the convenience of heavily laden carts passing to and from the pontoon. ”

“ The end lifts which transfer the weight of the bridge to the piers when the span is closed consist of massive eccentrics having a throw of 4 in. The clearance is 2 in., so that the ends are lifted 2 in. This gives a load of 50 tons per eccentric. One motor is placed at each end of the span to operate the eccentrics and also to release the latches and raise the rails of the steam track.
At Riga there is a floating pontoon bridge over the Duna. It consists of fourteen rafts, 105 ft. in length, each supported by two pontoons placed 64 ft. apart. ”

“ Five pontoons, with their appurtenances, form the load of one carriage. Length, 15 feet; diameter, 1 foot 7 inches; displacement, 271⁄2 cubic feet; buoyancy, 1718 lb., or 151⁄4 cwt., from which deduct 2 cwt. for the weight of pontoon, and share of superstructure. A bridge of this nature is so light that it may be made on shore, and carried by hand entire. It will support as many men as can be placed on it, and, by removing the chesses over the gunnels, it may be bent so as to be passed without difficulty down a steep bank, or counterscarp. ”

“ Pontoon Bridge.
101At the head of the mill-race, where the channel was fifty feet wide, we built a pontoon bridge. We were fortunate in securing six good cider barrels at low cost, also a quantity of “slabs” from one of the sawmills of Lumberville. ”

“ But the crowning work of this corps, as it always seemed to me, the department of their labor for which, I believe, they will be the longest remembered, was that of ponton-bridge laying. The word ponton, or pontoon, is borrowed from both the Spanish and French languages, which, in turn, derive it from the parent Latin, pons, [382] meaning a bridge, but it has now come to mean a boat, and the men who build such bridges are called by the French pontoniers. In fact, the system of ponton bridges in use during the Rebellion was copied, I believe, almost exactly from the French model. ”

“ What have you got on the east bank that needs looking after?
“Pontoon—one big pontoon with the overhead crane on it. T’other overhead crane on the mended pontoon, with the cart-road rivets from Twenty to Twenty-three piers—two construction lines, and a turning-spur. The pilework must take its chance,” said Hitchcock.
“All right. Roll up everything you can lay hands on. We’ll give the gang fifteen minutes more to eat their grub.”
Close to the verandah stood a big night-gong, never used except for flood, or fire in the village. ”

“ When Goodyear's ideas are carried out, it will be by pontoons of inflated India-rubber that rivers will be crossed. A pontoon-train will then consist of one wagon drawn by two mules; and if the march is through a country that furnishes the wooden part of the bridge, a man may carry a pontoon on his back in addition to his knapsack and blanket. ”

“ For the passage of rivers, each army corps had a pontoon-train with a detachment of engineers, and, on reaching a river, the leading infantry division was charged with the labor of putting it down. Generally the single pontoon-train could provide for nine hundred feet of bridge, which sufficed; but when the rivers were very wide two such trains would be brought together, or the single train was supplemented by a trestle-bridge, or bridges made on crib-work, out of timber found near the place. ”

“ The service-pontoon, as arranged by General Cullum, is composed of three connected cylinders of rubber-coated canvas, each having three compartments. On these pontoons, when inflated, the bridge-table is built, lashed, and anchored. This bridge has remarkable portability, but it has also serious defects. The oxidation of the sulphur in vulcanized rubber produces sulphuric acid in sufficient amount to impair the strength of the canvas-fibres, thus causing eventual decay, rendering it prudent to renew the pontoons after a year's campaigning. ”

“ My recollection is that Hains built a raft bridge; McPherson a pontoon, using cotton bales in large numbers, for pontoons; and that Ransom felled trees on opposite banks of the river, cutting only on one side of the tree, so that they would fall with their tops interlacing in the river, without the trees being entirely severed from their stumps. A bridge was then made with these trees to support the roadway. Lumber was taken from buildings, cotton gins and wherever found, for this purpose. By eight o'clock in the morning of the 18th all three bridges were complete and the troops were crossing. ”

“ Dimensions of colonel Congreve’s Wooden Pontoons.
The common pontoons will support a weight of 4 or 5000 pounds. They are generally placed, in forming a bridge, about their own width asunder. See Bridge.
Pontoon carriage, was made with two wheels only, and two long side pieces, whose fore-ends are supported by a limber; and served to carry the pontoon, boards, cross timbers, anchors, and every other thing necessary for making a bridge; but better experience places them on four wheels. ”

“ Our national eminence in the art of building wooden trussed and suspension bridges is proof enough that whatever can be done to improve on the military bridge-trains of Europe may be expected at our hands. We shall not lack inventiveness; let us be as careful not to lack judgment, and by all means to be fair and honest in seeking for the best system. When the experience of this war can be generalized, a more positive pontoon-system will be exacted for our service. ”

“ General Cullum briefly describes the various bridge-systems employed in the different services of the world, including the galvanized iron boat system, the Blanchard metal cylinder system, the Russian and Fowke's systems of canvas stretched over frames, the Birigo system, the French bateau system, the various trestle systems, and many others. The French wooden bateau is the pontoon chiefly used in our service, and it is specially commended by its thoroughly proved efficiency, and by its utility as an independent boat. ”

“ The baulks (or road-bearers) and chesses (or planks) remain unaltered, but chess-holders and chess-bearers are added for use in constructing light bridges for infantry in file. Inj this kind of bridge each pontoon section is used separately, with 'a roadway of chesses' placed longitudinally four abreast. In the normal or medium bridge two sections, and in heavy bridge
three sections are joined together. The chief advantages of the
equipment are (1) the buoyancy of the piers can be proportioned to the weight of traffic and to the roughness of the water ”

“ The mooring chains, weighing 22 lb per ft., are taken from the upstream end of each pontoon to a downstream screw pile mooring and from the downstream end to an upstream screw pile.
13. Transporter Bridges.—This new type of bridge consists of a high level bridge from which is suspended a car at a low level. The car receives the traffic and conveys it across the river, being caused to travel by electric machinery on the high level bridge. Bridges of this type have been erected at Portugalete, Bizerta, Rouen, Rochefort and more recently across the Mersey between the towns of Widnes and Runcorn. ”

“ There are twenty-eight of these pontoons, each 160 feet long and ten feet broad; they are each divided into eleven water-tight compartments, and moored both up and down stream by means of iron cables. Viewed from the lower part of the harbor as one approaches from the sea, the bridge appears like a massive fixed structure, and we could hardly believe the captain of the steamer when he told us that it was only a floating affair, resting on pontoons.
"There, we've described the bridge the best way we can, and the Doctor says it is very well done for inexperienced boys like ourselves. ”

“ To our left, a channel lies under giant steel bridges. Our course is not there: we are piloted towards a dock for passenger and cargo ships, and entering it in a hot glare, and colouring that almost sears, of sky and water and paint, we make our berth, wallowing once over the water’s breadth to the anger of lesser navigators, who go by in their boats bawling at the bridge in general. The handsome passenger boats with their great paddle-wheels and their red awnings lie opposite our plebeian resting-place: beside a grimy wharf, where small cranes and coal carts seem to multiply. ”

“ These bridges form great impediments to the traffic, both on land and by water ; for the pontoon is never pulled up to make a passage until about a dozen junks and boats have collected, and their owners, who by that time have been long waiting for the event, are clamouring and fighting amongst themselves to get first through. While the boats are passing through, the land traffic is of course interrupted, and crowds of foot passengers and vehicles are pressing forward on each side of the aperture to await the replacement of the pontoon. ”

“ The materials for these bridges, which are known as Ponton Bridges, are loaded upon wagons and accompany the army on its marches, and when required for use the bridge is rapidly put together, piece by piece, in accordance with fixed rules, which constitute, in fact, a regular drill. The wooden boats are quite heavy and are used for heavy traffic, but for light work, as, for example, to accompany the rapid movements of the cavalry, boats made of heavy canvas, stretched upon light wooden frames, that are put together on the spot, are used. ”

“ Where the topographical conditions are such that bridges can be made of such heights, without prohibitive cost, as to permit, at all navigable stages of water, the passage of boats best suited to the river commerce, it is for the best interest of both the land traffic and the river traffic that bridges be so constructed. ”

“ The third and fourth plans propose to construct a draw for the passage of boats, in the suspension or the western bridge.
Draws are common in bridges across arms of the sea where the tide ebbs and flows, for the passage of sea vessels, and also in bridges over rivers with a sluggish current; but we entertain great doubts whether a draw in either of the bridges, as proposed, can be constructed so as to afford 'a convenient and safe passage' for the steamboats that ply upon the Ohio. Some of them are about two hundred and fifty feet long, and from fifty to sixty feet in width. ”

“ They have a rise of sixty feet, sufficient to permit the passage of steamers under them, even at high water. The piers are sunk through the sand to the bed-rock, a distance of from ninety to one hundred and twenty feet, the work having been accomplished by means of iron wrought caissons and atmospheric pressure. Each span consists of four ribbed arches, made of cast steel. The bridge is two stories high, the lower story containing a double car track, and the upper one two horse-car tracks, two carriageways and two foot-ways. ”

“ In 1896 it was farther extended to the north, and its length is now 2478 ft. and its breadth 80 ft. It is supported on floating pontoons about 200 in number, connected with the river wall by eight bridges, besides a floating bridge for heavy traffic 550 ft. in length and 35 ft. ”

“ Another type of frame-bridge is the cantilever, which has been used in Indian frontier expeditions to bridge swift steep-banked streams. Improvised suspension bridges are also used. Floating bridges are made not only of pontoons but also of boats of all sorts, casks lashed together, and rafts. They are almost always combined with one or two bays of trestle bridging at the shore ends. ”