Iron Bridges. Illustrated History of their Construction

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IRON BRIDGES AND THEIR CONSTRUCTION

"ASSEMBLING" BRIDGE UNDER SHED.

In a graveyard in Watertown, a village near Boston, Massachusetts, there isa tombstone commemorating the claims of the departed worthy who lies below tothe eternal gratitude of posterity.

The inscription is dated in the early part of this century (about 1 1!", butthe name of him who was thus immortali#ed has faded li$e the date of his deathfrom my memory, while the deed for which he was distinguished, and which wasrecorded upon his tombstone, remains clear.

%&e built the famous bridge over the 'harles iver in this town,% says therecord. The 'harles iver is here a small stream, about twenty to thirty feet wide,

and the bridge was a simple wooden structure.

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THE LYMAN VIADUCT

oubtless in its day this structure was considered an engineering featworthy of such posthumous immortality as is gained by an epitaph, and afforded

such convenience for transportation as was needed by the commercial activity ofthat era. rom that time, however, to this, the changes which have occurred inour commercial and industrial methods are so fully indicated by the changes ofour manner and method of bridge)building that it will not be a loss of time toinvestigate the present condition of our abilities in this most useful branch ofengineering s$ill.

In the usual archaeological classification of eras the /tone 0ge precedesthat of Iron, and in the history of bridge)building the same se uence has beenpreserved. Though the $nowledge of wor$ing iron was ac uired by many nationsat a pre)historic period, yet in uite modern times2within this century, even2the

invention of new processes and the e3perience gained of new methods have socompletely revolutioni#ed this branch of industry, and given us such a masteryover this material, enabling us to apply it to such new uses, that for the futurethe real 0ge of Iron will date from the present century.



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The $nowledge of the arch as a method of construction with stone or bric$2both of them materials aptly fitted for resistance under pressure, but ofcomparatively no tensile strength2enabled the omans to surpass all nationsthat had preceded them in the course of history in building bridges. The bridgeacross the anube, erected by 0pollodorus, the architect of Tra4an5s 'olumn, wasthe largest bridge built by the omans. It was more than three hundred feet in

height, composed of twenty)one arches resting upon twenty piers, and was abouteight hundred feet in length. It was after a few years destroyed by the emperor0drian, lest it should afford a means of passage to the barbarians, and its ruinsare still to be seen in *ower &ungary.

With the advent of railroads bridge)building became even a greaternecessity than it had ever been before, and the use of iron has enabled engineersto grapple with and overcome difficulties which only fifty years ago would havebeen considered hopelessly insurmountable. In this modern use of iron advantageis ta$en of its great tensile strength, and many iron bridges, over whichenormous trains of heavily)loaded cars pass hourly, loo$ as though they were

spun from gossamer threads, and yet are stronger than any structure of wood orstone would be.



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BLAST-FURNACES

0nother great advantage of an iron bridge over one constructed of wood orstone is the greater ease with which it can, in every part of it, be constantlyobserved, and every failing part replaced. Whatever material may be used, everyedifice is always sub4ect to the slow disintegrating influence of time and theelements. In every such edifice as a bridge, use is a process of constantwea$ening, which, if not as constantly guarded against, must inevitably, in time,lead to its destruction.



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DUMPING ORE AND COAL INTO BLAST-FURNACES

In a wooden or stone bridge a beam affected by dry rot or a stonewea$ened by the effects of frost may lie hidden from the inspection of even themost vigilant observer until, when the process has gone far enough, the bridgesuddenly gives way under a not unusual strain, and death and disaster shoc$ thecommunity into a sense of the inherent defects of these materials for suchstructures.

The introduction of the railroad has brought about also another change inthe bridge)building of modern times, compared with that of all the ages whichhave preceded this nineteenth century. The chief bridges of ancient times werebuilt as great public conveniences upon thoroughways over which there was alarge amount of travel, and conse uently were near the cities or commercialcentres which attracted such travel, and were therefore placed where they wereseen by great numbers.

6ow, however, the connection between the chief commercial centres ismade by the railroads, and these penetrate immense distances, throughcomparatively unsettled districts, in order to bring about the needed distribution7and in conse uence many of the great railroad bridges are built in the mostunfre uented spots, and are unseen by the numerous passengers who traversethem, unconscious that they are thus easily passing over specimens ofengineering s$ill which surpass, as ob4ects of intelligent interest, many of thesights they may be traveling to see.



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ELEVATOR

The various processes by which the iron is prepared to be used in bridge)

building are many of them as new as is the use of this material for this purpose,and it will not be amiss to spend a few moments in e3amining them beforepresenting to our readers illustrations of some of the most remar$able structuresof this $ind.



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Ta$ing a train by the eading ailroad from -hiladelphia, we arrive, inabout an hour, at -hoeni3ville, in the /chuyl$ill 8alley, where the -hoeni3 Iron)and Bridge)wor$s are situated. In this establishment we can follow the iron fromits original condition of ore to a finished bridge, and it is the only establishment inthis country, and most probably in the world, where this can be seen.

THE ENGINE-ROOM

These wor$s were established in 19:!. In 1 ;9 they came into thepossession of the late avid eeves, who by his energy and enterprise increasedtheir capacity to meet the growing demands of the time, until they reached theirpresent e3tent, employing constantly over fifteen hundred hands.



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RUNNING METAL INTO PIGS



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The first process is melting the ore in the blast)furnace. &ere the ore, withcoal and a flu3 of limestone, is piled in and sub4ected to the heat of the fires,driven by a hot blast and $ept burning night and day. The iron, as it becomesmelted, flows to the bottom of the furnace, and is drawn off below in a glowingstream. Into the top of the blast)furnaces the ore and coal are dumped, havingbeen raised to the top by an elevator wor$ed by a blast of air. It is curious to

notice how slowly the e3perience was gathered from which has re suited theability to wor$ iron as it is done here.

Though even at the first settlement of this country the forests of ohn avenson the ne3tyear, and in 1=1: another to *ord udley7 yet the process did not come intogeneral use until nearly a hundred years later.

CARRYING THE IRON BALLS

The blast for the furnace is driven by two enormous engines, each of threehundred horse)power. The blast used here is, as we have said, a hot one, the airbeing heated by the consumption of the gases evolved from the material itself.The gradual steps by which these successive modifications were introduced is anevidence of how slowly industrial processes have been perfected by the collectivee3perience of generations, and shows us how much we of the present day owe toour predecessors.



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rom the earliest times, as among the native smiths of 0frica to)day, theblast of a bellows has been used in wor$ing iron to increase the heat of thecombustion by a more plentiful supply of o3ygen. The blast)furnace is supposedto have been first used in Belgium, and to have been introduced into


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In his e3periments for perfecting his process Mr. 'ort spent his fortune, andthough it proved so valuable, he died poor, having been involved by thegovernment in a lawsuit concerning his patent which beggared him. /i3 yearsbefore his death, the government, as an ac$nowledgment of their wrong, grantedhim a yearly pension of a thousand dollars, and at his death this miserlyrecompense was reduced to his widow to si3 hundred and twenty)five dollars.

ROTARY SQUEEZER



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BOILING-FURNACE

When iron is simply melted and run into any mould, its te3ture is granular,and it is so brittle as to be uite unreliable for any use re uiring much tensilestrength. The process of puddling consisted in stirring the molten iron run out in apuddle, and had the effect of so changing its atomic arrangement as to renderthe process of rolling it more efficacious. The process of boiling is considered animprovement upon this.



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The boiling)furnace is an oven heated to an intense heat by a fire urgedwith a blast. The cast)iron sides are double, and a constant circulation of water is$ept passing through the chamber thus made, in order to preserve the structurefrom fusion by the heat. The inside is lined with fire)bric$ covered with metallicore and slag over the bottom and sides, and then, the oven being charged withthe pigs of iron, the heat is let on. The pigs melt, and the oven is filled with

molten iron.The puddler constantly stirs this mass with a bar let through a hole in the

door, until the iron boils up, or %ferments,% as it is called. This fermentation iscaused by the combustion of a portion of the carbon in the iron, and as soon asthe e3cess of this is consumed, the cinders and slag sin$ to the bottom of theoven, leaving the semi)fluid mass on the top. /tirring this about, the puddlerforms it into balls of such a si#e as he can conveniently handle, which are ta$enout and carried on little cars, made to receive them, to %the s uee#er.%



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THE ROLLS

To carry on this process properly re uires great s$ill and 4udgment in the

puddler. The heat necessarily generated by the operation is so great that veryfew persons have the physical endurance to stand it. /o great is it that theclothes upon the person fre uently catch fire. /uch a strain upon the physicalpowers naturally leads those sub4ected to it to indulge in e3cesses. Theperspiration which flows from the puddlers in streams while engaged in their wor$is caused by the natural effort of their bodies to preserve themselves from in4uryby $eeping their normal temperature.



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/uch a consumption of the fluids of the body causes great thirst, and thee3haustion of the labor, both bodily and mental, leads often to the e3cessive useof stimulants. In fact, the wor$ is too laborious. Its conditions are such that noone should be sub4ected to them. The necessity, however, for 4udgment,e3perience and s$ill on the part of the operator has up to this time prevented theintroduction of machinery to ta$e the place of human labor in this process. The

successful substitution in modern times of machines for performing variousoperations which formerly seemed to re uire the intelligence and de3terity of aliving being for their e3ecution, 4ustifies the e3pectation that the study now beinggiven to the organi#ation of industry will lead to the invention of machines whichwill obviate the necessity for human suffering in the process of puddling. /uch aconsummation would be an advantage to all classes concerned. The attemptswhich have been made in this direction have not as yet proved entirelysuccessful.

In the s uee#er the glowing ball of white)hot iron is placed, and forced witha rotary motion through a spiral passage, the diameter of which is constantly

diminishing. The effect of this operation is to s uee#e all the slag and cinder outof the ball, and force the iron to assume the shape of a short thic$ cylinder, called%a bloom.% This process was formerly performed by stri$ing the ball of ironrepeatedly with a tilt)hammer.



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COLD SAW

The bloom is now re)heated and sub4ected to the process of rolling. %Therolls% are heavy cylinders of cast iron placed almost in contact, and revolvingrapidly by steam)power. The bloom is caught between these rollers, and passedbac$ward and forward until it is pressed into a flat bar, averaging from four to si3inches in width, and about an inch and a half thic$.

These bars are then cut into short lengths, piled, heated again in a furnace,and re)rolled. 0fter going through this process they form the bar iron ofcommerce. rom the iron reduced into this form the various parts used in theconstruction of iron bridges are made by being rolled into shape, the rolls throughwhich the various parts pass having grooves of the form it is desired to give tothe pieces.



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HOT SAW

RIVETING A COLUMN



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These rolls, when they are driven by steam, obtain this generally from aboiler placed over the heating)or puddling)furnace, and heated by the wastegases from the furnace. This arrangement was first made by >ohn Criffin, thesuperintendent of the -hoeni3 Iron)wor$s, under whose direction the first rollediron beams over nine inches thic$ that were ever made were produced at thesewor$s.

The process of rolling toughens the iron, seeming to draw out its fibres7 andiron that has been twice rolled is considered fit for ordinary uses. or the variousparts of a bridge, however, where great toughness and tensile strength arenecessary, as well as uniformity of te3ture, the iron is rolled a third time. Thebars are therefore cut again into pieces, piled, re)heated and rolled again.

0 bar of iron which has been rolled twice is formed from a pile of fourteenseparate pieces of iron that have been rolled only once, or %muc$ bar,% as it iscalled7 while the thrice)rolled bar is made from a pile of eight separate pieces ofdouble)rolled iron. If, therefore, one of the original pieces of iron has any flaw ordefect, it will form only a hundred and twelfth part of the thrice)rolled bar. Theuniformity of te3ture and the toughness of the bars which have been thrice rolledare so great that they may be twisted, cold, into a $not without showing anysigns of fracture. The bars of iron, whether hot or cold, are sawn to the variousre uired lengths by the hot or cold saws shown in the illustrations, which revolvewith great rapidity.



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FURNACE AND HYDRAULIC DIE

or the columns intended to sustain the compressive thrust of heavyweights a form is used in this establishment of their own design, and to which thename of the %-hoeni3 column% has been given. They are tubes made from four orfrom eight sections rolled in the usual way and riveted together at their flanges.When necessary, such columns are 4oined together by cast)iron 4oint)bloc$s, withcircular tenons which fit into the hollows of each tube.

To 4oin two bars to resist a strain of tension, lin$s or eye)bars are usedfrom three to si3 inches wide, and as long as may be needed. 0t each end is anenlargement with a hole to receive a pin. In this way any number of bars can be

4oined together, and the result of numerous e3periments made at thisestablishment has shown that under sufficient strain they will part as often in thebody of the bar as at the 4oint. The heads upon these bars are made by a process$nown as die)forging. The bar is heated to a white heat, and under a die wor$edby hydraulic pressure the head is shaped and the hole struc$ at one operation.This method of 4oining by pins is much more reliable than welding. The pins aremade of cold)rolled shafting, and fit to a nicety.

The general view of the machine)shop, which covers more than an acre ofground, shows the various machines and tools by which iron is planed, turned,drilled and handled as though it were one of the softest of materials. /uch amachine)shop is one of the wonders of this century. Most of the operationsperformed there, and all of the tools with which they are done, are due entirely tomodern invention, many of them within the last ten years.



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By means of this application of machines great accuracy of wor$ isobtained, and each part of an iron bridge can be e3actly duplicated if necessary.This method of construction is entirely 0merican, the


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The calculations and plans are then made for the use of such dimensions ofiron that the strain upon any part of the structure shall not e3ceed a certainma3imum, usually fi3ed at ten thousand pounds to the s uare inch.

0s the weight of the iron is $nown, and its tensile strength is estimated atsi3ty thousand pounds per s uare inch, this estimate, which is technically called%a factor of safety% of si3, is a very safe one. In other words, the bridge isplanned and so constructed that in supporting its own weight, together with anyload of locomotives or cars which can be placed upon it, it shall not be sub4ectedto a strain over one)si3th of its estimated strength.

NEW RIVER BRIDGE ON ITS STAGING

0fter the plan is made, wor$ing drawings are prepared and the process ofmanufacture commences. The eye)bars, when made, are tested in a testing)machine at double the strain which by any possibility they can be put to in thebridge itself. The elasticity of the iron is such that after being submitted to atension of about thirty thousand pounds to the s uare inch it will return to itsoriginal dimensions7 while it is so tough that the bars, as large as two inches indiameter, can be bent double, when cold, without showing any signs of fracture.&aving stood these tests, the parts of the bridge are considered fit to be used.



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BRIDGE AT ALBANY

When completed the parts are put together2or %assembled,% as thetechnical phrase is2in order to see that they are right in length, etc. Then theyare mar$ed with letters or numbers, according to the wor$ing plan, and shippedto the spot where the bridge is to be permanently erected. Before the erectioncan be begun, however, a staging or scaffolding of wood, strong enough tosupport the iron structure until it is finished, has to be raised on the spot. Whenthe bridge is a large one this staging is of necessity an important and costlystructure.

0n illustration on another page shows the staging erected for the support ofthe 6ew iver bridge in West 8irginia, on the line of the 'hesapea$e and +hio

ailway, near a romantic spot $nown as &aw$snest. 0bout two hundred yardsbelow this bridge is a waterfall, and while the staging was still in use for itsconstruction, the river, which is very treacherous, suddenly rose about twentyfeet in a few hours, and became a roaring torrent.



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LA SALLE BRIDGE

The method of ma$ing all the parts of a bridge to fit e3actly, and securingthe ties by pins, is peculiarly 0merican. The plan still followed in


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The curved portion crosses the 0lbany basin, or outlet of the


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The bridge over the Eennebec iver, on the line of the Maine 'entralailroad, at 0ugusta, Maine, is another instance of a %through% bridge. It cost

seventy)five thousand dollars, has five spans of one hundred and eighty)five feeteach, and was built to replace a wooden dec$ bridge which was carried away by afreshet.

BRIDGE AT AUGUSTA, MAINE

The bridge on the -ortland and +gdensburg ailroad which crosses the/aco iver is a very general type of a through railway bridge. It consists of twospans of one hundred and eighty)five feet each, and cost twenty thousanddollars. The 6ew iver bridge in West 8irginia consists of two spans of twohundred and fifty feet each, and two others of seventy)five feet each. Its costwas about seventy thousand dollars. The *yman 8iaduct, on the 'onnecticut 0ir)line ailway, at


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SACO BRIDGE

The safety of a bridge depends uite as much upon the design andproportions of its details and connections as upon its general shape. The strainwhich will compress or e3tend the ties, chords and other parts can be calculated

with mathematical e3actness.But the strains coming upon the connections are very often indeterminate,

and no mathematical formula has yet been found for them. They are li$e thestrains which come upon the wheels, a3les and moving parts of carriages, carsand machinery.

Fet e3perience and 4udgment have led the best builders to a singularuniformity in their treatment of these parts.


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PHOENIX WORKS

There is no doubt that iron bridges can be made perfectly safe. Theirmargin is greater than that of the boiler, the a3les or the rail. To ma$e them safe,


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In the mean time, the best security for the safety of iron bridges is to befound in the self)interest of the railway corporations, who certainly do not desireto waste their money or to render themselves liable to damages from thebrea$ing of their bridges, and who conse uently will employ for suchconstructions those whose reputation has been fairly earned, and whosecharacter is such that reliance can be placed in the honesty of their wor$.

Iron Bridges. Illustrated History of their Construction

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