Iron bridge

“ We often hear iron bridges condemned, while wooden ones, so called, are supposed to be free from defects. It does not seem to occur to persons holding such ideas, that wooden bridges rely just as much upon the strength of the iron rods that tie the timbers together, as upon the timber. As a matter of fact, where one iron bridge [Pg 62] falls, a dozen wooden ones do the same thing. One very decided advantage which an iron bridge has over a wooden one, is that we can make sure of good iron in the beginning, and that we can also be sure that it does not decay ”

“ The Keystone Bridge Works have always been a source of satisfaction to me. Almost every concern that had undertaken to erect iron bridges in America had failed. Many of the structures themselves had fallen and some of the worst railway disasters in America had been caused in that way. Some of the bridges had given way under wind pressure but nothing has ever happened to a Keystone bridge, and some of them have stood where the wind was not tempered. There has been no luck about it. We used only the best material and enough of it, making our own iron and later our own steel. ”

“ To this, it may be replied, that no iron bridge, made by a reliable company, has ever shown the slightest indication of any thing of the kind, though they have been used for many years in Russia, Norway, Sweden, and Canada, and nothing that we know in regard to iron gives us any reason to suppose that any thing of the kind ever will happen. But here, again, every thing turns upon the quality of the iron. ”

“ We have yet to learn why engineers have abandoned the arched bridge for the wrought iron girder system, except that the latter is considered more economical, and better fitted for bearing tensile stress. Cast-iron bridges constructed as rigid arches, subject to compression and composed of small parts, have all the mechanical advantages of stone without some of its drawbacks, while artistically they can be made satisfactory erections.--Building News. ”

“ So judicious was the selection of its site, and so great its utility, that a thriving town of the name of Ironbridge has grown up around it upon what, at the time of its erection, was a nameless part of "the waste of the manor of Madeley." And it is probable that the bridge will last for centuries to come. Thus, also, was the use of iron as an important material in bridge-building fairly initiated at Coalbrookdale by Abraham Darby, as the use of iron rails was by Richard Reynolds. ”

“ It is no use my reminding you that no railroad goes to the old home place. It isn't there any more, even in outward seeming. Cummins's woods, where you had your robbers' cave, is all cleared off and cut up into building lots. The cool and echoing covered bridge, plastered with notices of dead and forgotten Strawberry Festivals and Public Vendues, has long ago been torn down to be replaced by a smart, red iron bridge. The Volunteer Firemen's Engine-house, whose brick wall used to flutter with the gay rags of circus-bills, is gone as if it never were at all. ”

“ If, from such records, we find an iron bridge built twenty-five years ago by an unknown company, with iron, at best, of a doubtful quality, and having a factor of three or four for the rolling-stock and speeds of twenty years ago, instead of a factor of six for the rolling-stock and speeds of to-day, we had better remove that bridge before it removes itself. ”

“ At the celebration of the opening of the North Wales Railway at Bangor, almost within sight of his iron bridge across the Straits of Menai, Robert Stephenson said, "We are daily producing from the bowels of the earth a raw material, in its crude state apparently of no worth, but which, when converted into a locomotive engine, flies over bridges of the same material, with a speed exceeding that of the bird, advancing wealth and comfort throughout the country. ”

“ The bridge, which was built soon after the road was finished, is now found to be wholly inadequate, and a new double track bridge is soon to take the place of the old one,—one not so very old either. It seems a pity that so much labor should be rendered useless. The iron piers were driven down, section by section, into the shifting bed of the river, until men were working at the peril of their lives down seventy or eighty feet below the water, and these piers rise sixty feet above the river, and support an immense iron bridge ”

“ That the model is strong, and that a bridge constructed on the same principles will also be strong, they appear to be well agreed in, but to what particular causes to assign the strength they are not agreed in. The Committee was directed by the Academy to examine all the models and plans for iron bridges that had been proposed in France, and they unanimously gave the preference to our own, as being the simplest, strongest, and lightest. ”

“ Cast-iron girder, thirty feet span, load thirty-three tons.
Mr. W. H. Barlow, (Eng.) observed, “that in case of a timber viaduct, a freight train, at a low speed, produced a certain deflection; but an extra train, with a much lighter engine, seemed to push the bridge like a wave before it.”
The Britannia tubular bridge was depressed three fourths of an inch by two locomotives and a train of two hundred and eighty tons standing still; but at seventy miles per hour, the deflection was sensibly less.
192 CHAPTER IX.
IRON BRIDGES.
“A little knowledge is a dangerous thing.” ”

“ Everything is done by the aid of air, steam, and water. Muscle will be in little demand, brains at a premium. In 1832 cast-iron bridges existed of short span, but wrought-iron had not been used. To-day we think little of trusses of 500 feet span, and suspension-bridges of 1,000 feet; while it is proposed to build a steel truss-bridge over a mile long, with two spans of 1,700 feet each. In the power-printing press, an invention of the eighteenth century, we find that the last half-century has wrought wonders. ”

“ An important bridge on the Pennsylvania Railroad had recently burned and the traffic had been obstructed for eight days. Iron was the thing. I proposed to H.J. Linville, who had designed the iron bridge, and to John L. Piper and his partner, Mr. Schiffler, who had charge of bridges on the Pennsylvania line, that they should come to Pittsburgh and I would organize a company to build iron bridges. It was the first company of its kind. I asked my friend, Mr. Scott, of the Pennsylvania Railroad, to go with us in the venture, which he did. Each of us paid for a one fifth interest, or $1250. ”

“ In his case, however, success came early, and within three years he had advanced so far in means and reputation, that he was intrusted with the contract for iron bridges on the Glasgow, Hamilton, and Bothwell Railway, one of them being a very large structure spanning the Clyde. ”

“ What do we know to-day of the quality of the iron rods in any wooden bridge in Massachusetts? It is very doubtful if the best inspection we have in the United States at the present time would have found any defect so evident in the Tariffville bridge as to condemn it as unfit for the passage of trains. There are hundreds of exactly such bridges all over New England, as far as we can tell by the best inspection we now have, made on the same plan, with no more material, and of which we know just as little of the quality of the iron as we did in the Tariffville bridge. ”

“ Across this burning ditch, through the middle of the doorway, was a bridge of two planks, one copper, the other iron—symbolic of the bridge thrown down by the Immortal Tahtsunye and by which the Five Patriarchs escaped from Shaolintze. Over this 242bridge hung an arch of pendent swords glowing and quivering with the heat that rose from the furnace below. The only lights in the Hall—unless the stars are numbered—were the ditch of fire and in the centre two iron racks, where blazed bundles of fagots and which gave an uncertain enormity to the shadows within. ”

“ It is perfectly well known by engineers the world over, that with good iron properly used, nothing of the kind ever takes place. This matter used to be a favorite bone of contention among engineers, but it has long since been laid upon the shelf. No engineer at the present day ever thinks of it. We have only to allow the proper margin for safety, as our first-class builders all do, and this antiquated objection at once vanishes. The examples of the long duration of iron in large bridges are numerous and conclusive. ”

“ Over this bridge of ropes, which is erected near Santa, travellers with loaded mules can pass in safety.
But suspension bridges composed of stronger and more durable materials than twisted fibres and tendrils of plants, are found to exist in these remote and semi-barbarous regions; in Thibet, as well as in China, many iron suspension bridges have been discovered, and it is no improbable conjecture that in countries so little known and visited by Europeans, others may exist, of which we have as yet received no accounts. ”

“ The bridge was opened for traffic in 1779, and proved a most serviceable structure. In 1788 the Society of Arts recognised Mr. Darby's merit as its designer and erector by presenting him with their gold medal; and the model of the bridge is still to be seen in the collection of the Society. Mr. Robert Stephenson has said of the structure: "If we consider that the manipulation of cast-iron was then completely in its infancy, a bridge of such dimensions was doubtless a bold as well as an original undertaking, and the efficiency of the details is worthy of the boldness of the conception." ”

“ 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." ”

“ A poor iron will often show a very fair breaking-strength, but, at the same time, will have a very low elastic limit, and be entirely unfit for use in a bridge. A piece of iron of very inferior quality will often sustain a greater load before breaking than a piece of the best and toughest material, for the reason that a tough but ductile iron will stretch before giving way, thus reducing the area of section, while a hard but poor iron will keep nearly its full size until it breaks. ”

“ Bollman’s bridge truss, of which the first example was built in 1850, has the very significant distinction of being the first bridging system in the world employing iron in all of its principal structural members that was used consistently on a railroad.
The importance of the transition from wood to iron as a structural and bridge building material is generally recognized, but it may be well to mention certain aspects of this change.
The tradition of masonry bridge construction never attained the great strength in this country which it held in Europe, despite a number of notable exceptions. ”

“ Many persons, in building wooden bridges, take no pains to get iron rods which are suitable for such work, but purchase what is easiest to be had in the market, and in many cases never find that the iron was bad until a bridge tumbles down. ”

“ Previous to the 19th century, the greatest bridges being constructed mostly of solid masonry piers and arches, no demand for a bridge of this kind existed; but after the use of wrought iron and steel became extensive in bridge making, and as these apparently light and airy frames may be extended, piece by piece across the widest rivers, straits, and arms of the sea, a substitute for the great, expensive, and frequent supporting piers became a want, and was supplied by the system of trusses and truss arches. ”

“ In one State a late annual report covers a whole railroad with the remark, "All of the bridges on this line are in excellent order;" and yet there were at that very time, and are now, on that road, several large wooden bridges with a factor of safety referred to the breaking-weight of not over two under a fair load, assuming the iron rods to be of the very best material,—a point upon which there is no evidence whatever. ”

“ Cast-iron bridges, being less liable to rust, cost less for painting than other metallic bridges; and if the cast iron is closed in by masonry, practically nothing; they do, indeed, [169] involve very little expenditure in the maintenance. Not being very amenable to repair or strengthening, cast-iron bridges commonly remain very much as built, or are reconstructed.
The proper care of timber bridges may become costly as the structure gains in age, and soon grow to a very wasteful expenditure. ”

“ A plank about eight inches broad hung longitudinally suspended across the river by means of roots and creepers wound over the chains with a slackness sufficient to allow the centre to sink to the depth of four feet below the chains. This bridge, called Selo-cha-zum, measured, from one side of the water to the other, 70 feet. The creepers are changed annually, and the planks are all loose; so that if the creepers give way in any part, they can be removed, and the particular part repaired without disturbing the whole.”
Numerous suspension bridges formed of iron chains exist also in China ”