Swing bridge

“ After entering Yünnan we came to a substantial200 suspension-bridge, made of eight parallel iron chains, and with chain hand-rails; but the planks on it were strewn about in a desultory way, calculated to upset unseasoned travellers. At either end of the bridge was a solid block of masonry, surmounted by a temple through which the chains passed and were buried deep into the ground. These bridges are often a considerable length, and do not hang at a natural swing, but are drawn up as tightly as possible with hawsers; which, of course, makes a heavy strain upon the chains. ”

“ Why has she not learnt to rule the world? Perhaps her body has been too numerous for her brain. On my table lies the photograph of a bridge which may be similar to the one admired by Athanase Kircher. It is an iron swing bridge in Western China, near Auhsien. There are three piers, two of stone, and the other a makeshift of two timber piles joined together at top by a log upon which the footway rests. The carpentry of the footway is primitive: across the long bearing beams, which are not at all thick or heavy, a great many slim laths lie unevenly ”

“ It may be necessary to say, in explanation of its construction, that on the five chains which support the platform, are placed several layers of strong coarse mats of bamboo, loosely put down, so as to play with the swing of the bridge; and that a fence on each side contributes to the security of the passenger.” The date of the erection of this bridge is unknown to the inhabitants of the country, and they even ascribe to it a fabulous origin. The length of this bridge appears to be about 150 feet. ”

“ It would be easy to write much more about primitive swing bridges, but enough has been said to stimulate thought and discussion. Not one of them has a brighter intelligence than that which we find in many prehistoric handicrafts. ”

“ Great marble bridges of a single span stretch from mountain to mountain over deep chasms. Nothing can be more imposing than the construction and the situation of those bridges, cast into space as it were, and swimming in the white, moist atmosphere which seems to fall regretfully into the ravine. The road passes from one side of the gorge to the other seven times in the space of four leagues. When our travellers crossed the seventh bridge, they saw at the bottom of the gorge, which widened almost imperceptibly before them, the charming valley of Luz, bathed in the flames of the rising sun. ”

“ A cantilever bridge consists of two inverted trussed beams, each balanced on a pier, one part extending over the river and the other to the shore, where it is firmly anchored in solid, heavy masonry. The ends extending over the river toward each other from the opposite piers are joined by a short truss in such a manner as to permit expansion and contraction consequent on changes of temperature, and yet be proof against vertical or lateral pressure. Such a bridge, it is said, sustains scarcely any strain in the center of the span. Each half of the entire bridge is self-balanced on its pier ”

“ You are standing aloft, balancing yourself upon tiny planks at the steadily advancing end of the bridge, as it forces itself over a stream of formidable width. Overhead, a gigantic, ungainly traveller, equipped with steel derricks at every corner, is advancing foot by foot as the bridge advances foot by foot. Underneath, through the thin network of planks, of girder and of supporting false work, you can see the surface of the river a full hundred feet below. ”

“ He crawls along fallen trees over some torrents and chasms; across a flooded river here and there he leaps in a shambling, lopsided fashion, when stepping-stones and boulders rise above water-level; he roams into hilly districts where many a ledge of rock spans a dangerous gap; but he enjoys himself most of all when a suspension bridge of branches enables him to amble from tree to tree across a deep-lying river pent up between high cliffs. ”

“ Hence each arch is complete and independent in itself, the piers having simply to sustain their vertical pressure. The arches are six in number, of 125 feet span each, the two approaches to the bridge being formed of cast-iron pillars and bearers in keeping with the arches.
The result is a bridge that for massive solidity may be pronounced unrivaled. It is one of the most magnificent and striking of the bridges to which railways have given birth, and has been worthily styled "the King of railway structures." ”

“ Now, in its simplest form, a suspension bridge has been known for ages. It is merely a pathway, or even a small movable car, suspended from a rope or ropes across a chasm. Ulloa describes suspension bridges built by the Peruvians in South America. Four stout cables span a river, and on these four is placed the platform of sticks and branches, while two other ropes connected with the platform are useful as hand rails. Such bridges sway with the wind and move with the passenger, but for light loads they appear to be perfectly safe. ”

“ It is a matter of notoriety that railroad bridges are built upon solid abutments of mason-work and resting on piers of stone between the abutments, thus giving strength and security to the frame above. It is not easy to see wherein such a structure differs from an ordinary bridge, except that, as it is to endure a greater burden, it is more solid and substantial. ”

“ Myself, I hate such a strumpet of a bridge as the Hoogesluis at Amsterdam, with her ornate spandrils, and her embossed masonry, and her balustraded parapet surmounted by a row of obelisks around which lamps are bracketed. Also I hate such a suspension bridge as the one at Conway Castle, where the metal rods that support the roadway pass through a brace of turrets on each of the embattled gateways. The effect is not only comic but ludicrous. No engineer with any sense would have put a metal viaduct within a few yards of Conway Castle. ”

“ When he gets on the suspension bridge, over the very top of the leap, he must hold by the rails to steady himself, and consider where he really is; the noise which the great body of water in the centre fall makes, when it descends into the pool beneath, dins his very ears, this with the broad rapid running river close beneath his feet as he stands on the light iron bridge, holding by a single rail with his hand, must almost take his sight away ”

“ 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. ”

“ The present Suspension Bridge which connects the South Stack rock with the Head, was formed in 1827. It is over a chasm 110 feet in width, and built on the same principle as the Menai Bridge, two chain cables passing across, firmly fixed in the rocks on either side, and carried over two massive stone pillars erected for the purpose. The chain supports the platform of timber five feet wide, and 70 feet above high-water mark. The crossing of the bridge to some will be a little trying to the nerves. ”

“ Instead of arches resting on piers and abutments, the bridge has a single arch, reaching from one side of the cutting to the other, and springing from the slopes, which it helps in some measure to support. A flying bridge of large dimensions near Weston-super-Mare carries a road across the cutting at a height of 60 feet above the line of rails, with a clear span of 110 feet. ”

“ On the lips of the abutment, the builders set two stone blocks, smooth and wide, and cut places in them for the bridge timbers. It was a piece of excellent judgment, since the great stones could not be broken from the abutment, and they were mighty enough to bear the weight of a mountain. The bridge rests on three sills, each a log that, unhewn, must have taken a dozen oxen to drag it. ”

“ The next step was the contrivance of arched beams or bowstring girders, firmly held together by horizontal ties to resist the thrust, instead of abutments. Numerous excellent specimens of this description of bridge were erected by Robert Stephenson on the original London and Birmingham Railway; but by far the grandest work of the kind—perfect as a specimen of modern constructive skill—was the High Level Bridge, which we owe to the genius of the same engineer. ”

“ Finally it was decided to build the railway along a hanging bridge. And this bridge is surely one of the most curious ever erected. From the cliff-face on either side, iron girders spring at an upward slant, like an inverted V, and from the point at which they meet, steel rods descend. These are securely fastened to the river-side of the bridge. The other side of the bridge is built into the cliff-face. Thus it is neither a suspension bridge nor an arch bridge, but is sustained by the strength of the overhead girders. ”

“ We wound up the narrow valley in splendid loops and curves, turning upon our tracks, running through numerous tunnels, and at one time crossing a chasm so narrow and with sides so steep and precipitous that it was found necessary to build the bridge in two parts, each against the face of the cliff, and then gradually lower them until they met above the river, three hundred and fifty feet below. ”

“ This bridge, a view of which is given in the cut below, is about two and a half miles below the falls, and spans the river near the head of the rapids, above the whirlpool. From pier to pier it is eight hundred feet long, and in breadth eight feet. It is suspended on eight wire cables, four on each side, which pass over towers fifty-four feet high, built of heavy timber. The present structure is only the scaffolding for constructing a larger bridge, intended for the passage of railroad cars. The towers for the large bridge will be of solid masonry, each eighty feet high. ”

“ Professor Fleeming Jenkin. If any reader wants to continue the study of timber bridges, let him turn to Colonel Emy and to the huge volumes compiled and edited by Hosking. But it is clear enough that timber bridges belong to the past; in these days they are ludicrously out of joint with the needs of social life, owing to the rapid advance which “progress” has made in artillery, in high explosives, in airships, and in aeroplanes.
[52] These date from about the year 1816, when Galashiels Bridge was constructed. ”

“ So the design is a clever feat not merely of repetitive decoration, but of repeating solids and voids that oppose each other in a harmony of contrasts; for the empty spandrils in their form oppose the leaf-shaped openings made by the arches, and all the curved solids of the bridge are foiled in a rugged manner by the upright columns, as well as by the long horizontal lines of the covered roadway. In the contrast between cold granite and warm brick there is colour also, and it suits the pulsating light and heat of Italy. ”

“ If we are going to Rhuddlan it will not be necessary for us to cross the shaking bridge, designed—perhaps—by Inigo Jones. I see no object in a bridge shaking, myself, but there are always those at hand who for a consideration will shake you the bridge if it gives you pleasure. ”

“ There are 20 chains, each of which is 20 perches or 300 palms in length. When many persons pass over together, the bridge vibrates to and fro, affecting them with horror and giddiness, lest whilst passing it should be struck with ruin. It is impossible to admire sufficiently the dexterity of the architect Sinensius, who had the hardihood to attempt a work so arduous, and so conducive to the convenience of travelling.” Another suspension bridge in this country is described in the 6th vol. ”

“ Sometimes a hanging bridge has to be crossed, spanning a horrid chasm, at the bottom of which roars a foaming torrent—the bridge itself, composed of ropes and brambles, all the while swinging like a hammock under the tread of the affrighted traveller! ”

“ As a rule, these road-bridges are simple and inexpensive in character, except in towns, or in cases where the line crosses the roads very obliquely, or where the road is situated at the top of a deep cutting, or bottom of a high embankment. Away from towns and out in the open country, permission is generally obtained to divert the roads to a moderate extent, so as to obtain a more favourable angle and height for the bridge; but in towns, where the roads become streets, sometimes of great width, with houses and shops on each side, little or no diversion can be allowed. ”

“ Of course, the bridge should not be difficultly or dangerously steep, but the necessary slope, whatever it may be, should be in the bridge itself, as far as the bridge can take it, and not pushed aside into the approach, as in our Waterloo road; the only rational excuse for doing which is that when the slope must be long it is inconvenient to put on a drag at the top of the bridge, and that any restiveness of the horse is more dangerous on the bridge than on the embankment. ”

“ But there is yet another thing about the old bridge for which I have cherished memories; that venerable buttonwood tree, gnarled and twisted into the quaintest and most comical deformity, that looms up from that high bank at the end of the lane. That bough which projects so far over the rippling surface, making a horizontal bend, like that of a man's arm, and then shooting up several yards at an obtuse angle, terminating in a mass of luxuriant foliage, was my favorite seat, when fishing, through many a long summer. ”