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diff --git a/30223-0.txt b/30223-0.txt new file mode 100644 index 0000000..d870345 --- /dev/null +++ b/30223-0.txt @@ -0,0 +1,1431 @@ +*** START OF THE PROJECT GUTENBERG EBOOK 30223 *** + +BRIDGE DISASTERS IN AMERICA + + _The Cause and the Remedy_ + + BY + + GEORGE L. VOSE + + AUTHOR OF "MANUAL FOR RAILROAD ENGINEERS AND ENGINEERING + STUDENTS," "LIFE AND WORKS OF GEORGE W. WHISTLER, + CIVIL ENGINEER," ETC. + + _"ETERNAL VIGILANCE IS THE PRICE OF LIBERTY"_ + + BOSTON + LEE AND SHEPARD PUBLISHERS + 10 MILK STREET + NEXT OLD SOUTH MEETING HOUSE + 1887 + + + + +NOTE. + + +The substance of the following pages appeared originally in "The +Railroad Gazette." It was afterwards reproduced in pamphlet form, and +has since been several times delivered as an address to various +bodies, the last occasion being before the Legislature of +Massachusetts, 1887. It is now re-published, with some new matter +added, in the hope that the public attention may be called to a +subject which has so important a bearing upon the public safety. + + + COPYRIGHT, 1887, + BY LEE AND SHEPARD. + + _All rights reserved._ + + + + +BRIDGE DISASTERS IN AMERICA. + + +Nearly all of the disasters which occur from the breaking down of +bridges are caused by defects which would be easily detected by an +efficient system of inspection. Not less than forty bridges fall in +the United States every year. No system of public inspection or +control at present existing has been able to detect in advance the +defects in these structures, or to prevent the disasters. After a +defective bridge falls, it is in nearly every case easy to see why it +did so. It would be just about as easy, in most cases, to tell in +advance that such a structure would fall if it ever happened to be +heavily loaded. Hundreds of bridges are to-day standing in this +country simply because they never happen to have received the load +which is at any time liable to come upon them. + +A few years ago an iron highway bridge at Dixon, Ill., fell, while a +crowd was upon it, and killed sixty persons. The briefest inspection +of that bridge by any competent engineer would have been sure to +condemn it. A few years later the Ashtabula bridge upon the Lake +Shore Railroad broke down under an express train, and killed over +eighty passengers. The report of the committee of the Ohio +Legislature appointed to investigate that disaster concluded, first, +that the bridge went down under an ordinary load by reason of +defects in its original construction; and, secondly, that the defects +in the original construction of the bridge could have been discovered +at any time after its erection by careful examination. Hardly had the +public recovered from the shock of this terrible disaster when the +Tariffville calamity added its list of dead and wounded to the long +roll already charged to the ignorance and recklessness which +characterize so much of the management of the public works in this +country. + +There are many bridges now in use upon our railroads in no way better +than those at Ashtabula and Tariffville, and which await only the +right combination of circumstances to tumble down. There are, by the +laws of chance, just so many persons who are going to be killed on +those bridges. There are hundreds of highway bridges now in daily +use which are in no way safer than the bridge at Dixon was, and which +would certainly be condemned by five minutes of competent and honest +inspection. More than that, many of them have already been condemned +as unfit for public use, but yet are allowed to remain, and invite +the disaster which is sure to come. Can nothing be done to prevent +this reckless and wicked waste of human life? Can we not have some +system of public control of public works which shall secure the +public safety? The answer to this question will be, Not until the +public is a good deal more enlightened upon these matters than it is +now. + +It has been very correctly remarked, that, in order to bring a +disaster to the public notice, it must be emphasized by loss of +life. The Ashtabula bridge fell, and killed over eighty persons; and +a storm of indignation swept over the country, from one end to the +other. No language was severe enough to apply to the managers of the +Lake Shore Railroad; but if that very bridge had fallen under a +freight-train, and no one had been injured, the occurrence would have +been dismissed with a paragraph, if, indeed, it had received even +that recognition. In February, 1879, a span one hundred and ten feet +long of an iron bridge on the Chicago and Alton Railroad at +Wilmington fell as a train of empty coal-cars was passing over it, +and three cars were precipitated into the river, a distance of over +thirty feet. No one was injured. Not a word of comment was ever made +in regard to this occurrence. Suppose, that, in place of empty +coal-cars, the train had consisted of loaded passenger-cars, and +that one hundred persons had been killed. We know very well what the +result would have been. Is not the company just as much to blame in +one case as the other? On the night of the 8th of November, 1879, one +span of the large bridge over the Missouri at St. Charles gave way as +a freight-train was crossing it, and seventeen loaded stock-cars fell +a distance of eighty feet into the river. Two brakemen and two +drovers were killed. This bridge, says the only account that appeared +in the papers, did not break apparently, for the whole span "went +down" with the cars upon it. It could hardly make much difference to +the four men who were killed, whether the bridge broke down, or +"went" down. Not a word of comment was ever made in the papers +outside of Missouri in regard to this disaster. Suppose, that, in +place of seventeen stock-cars, half a dozen passenger-cars had fallen +from a height of eighty feet into the river, and that, in place of +killing two brakemen and two drovers, two or three hundred passengers +had been killed. Is not the public just as much concerned in one case +as in the other? + +Suppose that a bridge now standing is exactly as unsafe as the +Ashtabula bridge was the day before it fell, would it be possible to +awaken public attention enough to have it examined? Probably not. +About two years ago an attempt was made to induce one of the leading +dailies in this country to expose a wretchedly unsafe bridge in New +England. The editor declined, on the ground that the matter was not +of sufficient interest for his readers; but less than a month +afterwards he devoted three columns of his paper to a detailed +account of a bridge disaster in Scotland, and asked why it was that +such things must happen, and if there was no way of determining in +advance whether a bridge was safe, or not? + +This editor certainly would not maintain, that, in itself, it was +more important to describe a disaster after it had occurred than to +endeavor to prevent the occurrence; but, as a business man, he knew +perfectly well that his patrons would read an account giving all of +the sickening detail of a terrible catastrophe, while few, if any, +would wade through a dry discussion of the means for protecting the +public from just such disasters. The public is always very indignant +with the effect, but does not care to trouble itself with the cause; +but the effect never will be prevented until the cause is +controlled; and the sooner the public understands that the cause is +in its own hands, to be controlled, or not, as it chooses, the sooner +we shall have a remedy for the fearful disasters which are altogether +too common in the United States. + +In a country where government controls all matters on which the +public safety depends, and where no bridge over which the public is +to pass is allowed to be built except after the plans have been +approved by competent authority, where no work can be executed except +under the rigid inspection of the best experts, nor opened to the +public until it has been officially tested and accepted, it makes +little or no difference whether the public is informed, or not, upon +these matters; but in a country like the United States, where any man +may at any time open a shop for the manufacture of bridges, whether +he knows any thing about the business, or not, and is at liberty to +use cheap and insufficient material, and where public officers are +always to be found ready to buy such bridges, simply because the +first cost is low, and to place them in the public ways, it makes a +good deal of difference. There is at present in this country +absolutely no law, no control, no inspection, which can prevent the +building and the use of unsafe bridges; and there never will be until +the people who make the laws see the need of such control. + +There is no one thing more important in this matter than that we +should be able to fix precisely the blame in case of disaster upon +some person to whom the proper punishment may be applied. If every +railway director, or town or county officer, knew that he was held +personally accountable for the failure of any bridge in his charge, +we should soon have a decided improvement in these structures. If we +could show that a certain bridge in a large town had been for a long +time old, rotten, worn out, and liable at any moment to tumble down, +and could show in addition, that the public officers having charge of +such a bridge knew this to be the case, and still allowed the public +to pass over it, we can see at once, that, in case of disaster, the +blame would be clearly located, and the action for damages would be +short and decisive. Once let a town have heavy damages to pay, and +let it know at the same time that the town officers are clearly +accountable for the loss, and it is possible that it would be willing +to adopt some system that should prevent the recurrence of such an +outlay. + +To see what may be accomplished by an efficient system of public +inspection, it is necessary to know something in regard to the +structures to be inspected. We have now in common use in this +country, both upon our roads and our railroads, bridges made entirely +of iron, bridges of wood and iron combined, and occasionally, though +not often nowadays, a bridge entirely of wood; and these structures +are to be seen of a great variety of patterns, of all sizes, and in +every stage of preservation. Of late so great has been the demand for +bridge-work, that this branch of engineering has become a trade by +itself; and we find immense works fitted up with an endless variety +of the most admirably adapted machine-tools devoted exclusively to +the making of bridges of wood, iron, steel, or all combined. As in +all division of labor, the result of this specialization has been to +improve the quality of the product, to lessen the cost, and to +increase the demand, until many of our large firms reckon the length +of bridging which they have erected by miles instead of feet. As +usual, however, in such cases, unprincipled adventurers are not +wanting, who, taking advantage of a great demand, do not hesitate to +fit up cheap shops, to buy poor material, and to flood the market +with a class of bridges made with a single object in view, viz., to +sell, relying upon the ignorance--or something worse--of public +officials for custom. Not a year passes in which some of these +wretched traps do not tumble down, and cause a greater or less loss +of life, and at the same time, with uninformed people, throw +discredit on the whole modern system of bridge-building. This evil +affects particularly highway bridges. The ordinary county +commissioner or selectman considers himself amply competent to +contract for a bridge of wood or iron, though he may never have given +a single day of thought to the matter before his appointment to +office. The result is, that we see all over the country a great +number of highway bridges which have been sold by dishonest builders +to ignorant officials, and which are on the eve of falling, and await +only an extra large crowd of people, a company of soldiers, a +procession, or something of the sort, to break down. + +Not many years ago, a new highway bridge of iron was to be made over +one of the principal rivers in New England. The county commissioners +desired a well-known engineer, especially noted as a bridge-builder, +to superintend the work, in order to see that it was properly +executed. The engineer, after inspection of the plans, told the +commissioners plainly that the design was defective, and would not +make a safe bridge; and that, unless it was materially changed, he +would have nothing to do with it. The bridge, however, was a cheap +one, and, as such, commended itself to the commissioners, who +proceeded to have it erected according to the original plan; and +these same commissioners now point to that bridge, which has not yet +fallen, but which is liable to do so at any time, as a complete +vindication of their judgment, so called, as opposed to that of the +engineer who had spent his life in building bridges. + +An impression exists in the minds of many persons, that it is purely +a matter of opinion whether a bridge is safe, or not. In very many +cases, however,--perhaps in most,--it is not at all a matter of +opinion, but a matter of fact and of arithmetic. The whole question +always comes to this: Is the material in this bridge of good quality? +Is there enough of it? Is it correctly disposed, and properly put +together? With given dimensions, and knowing the load to be carried, +it is a matter of the very simplest computation to fix the size of +each member. We know what one square inch of iron will hold, and we +know, also, the total number of pounds to be sustained; and it is no +matter of opinion, but one of simple division, how many times one +will go into the other. + +But it may be asked, Can the precise load which is coming upon any +structure be exactly fixed? are not the circumstances under which +bridges are loaded very different? Bridges in different localities +are certainly subjected to very different loads, and under very +different conditions; but the proper loads to be provided for have +been fixed by the best authority for all cases within narrow enough +limits for all practical purposes. Few persons are aware of the +weight of a closely packed crowd of people. Mr. Stoney of Dublin, one +of the best authorities, packed 30 persons upon an area of a little +less than 30 square feet; and at another time he placed 58 persons +upon an area of 57 square feet, the resulting load in the two cases +being very nearly 150 pounds to the square foot. "Such cramming," +says Mr. Stoney, "could scarcely occur in practice, except in +portions of a strongly excited crowd; but I have no doubt that it +does occasionally so occur." "In my own practice," he continues, "I +adopt 100 pounds per square foot as the standard working-load +distributed uniformly over the whole surface of a public bridge, and +140 pounds per square foot for certain portions of the structure, +such, for example, as the foot-paths of a bridge crossing a navigable +river in a city, which are liable to be severely tried by an excited +crowd during a boat-race, or some similar occasion." Tredgold and +Rankine estimate the weight of a dense crowd at 120 pounds per square +foot. Mr. Brunel used 100 pounds in his calculations for the +Hungerford Suspension Bridge. Mr. Drewry, an old but excellent +authority, observes that any body of men marching in step at from 3 +to 3-1/2 miles an hour will strain a bridge at least as much as +double the same weight at rest; and he adds, "In prudence, not more +than one-sixth the number of infantry that would fill a bridge should +be permitted to march over it in step." Mr. Roebling says, in +speaking of the Niagara Falls Suspension Bridge, "In my opinion, a +heavy train, running at a speed of 20 miles an hour, does less injury +to the structure than is caused by 20 heavy cattle under full trot. +Public processions marching to the sound of music, or bodies of +soldiers keeping regular step, will produce a still more injurious +effect." + +Evidently a difference should be made in determining the load for +London Bridge and the load for a highway bridge upon a New-England +country road in a thinly settled district. A bridge that is strong +enough is just as good and just as safe as one that is ten times +stronger, and even better; for in a large bridge, if we make it too +strong, we make it at the same time too heavy. The weight of the +structure itself has to be sustained, and this part of the load is a +perpetual drag on the material. + +In 1875 the American Society of Civil Engineers, in view of the +repeated bridge disasters in this country, appointed a committee to +report upon The Means of Averting Bridge Accidents. We might expect, +when a society composed of some hundreds of our best engineers +selects an expert committee of half a dozen men, that the best +authority would be pretty well represented; and such was eminently +the case. It would be impossible to have combined a greater amount of +acknowledged talent, both theoretical and practical, with a wider and +more valuable experience than this committee possessed. The first +point taken up in the report is the determination of the loads for +which both railroad and highway bridges should be proportioned. In +regard to highway bridges, a majority of the committee reported that +for such structures the standard loads should not be less than as +shown in the following table:-- + + +-------------------+----------+----------+----------+ + | | POUNDS PER SQUARE FOOT. | + | SPAN. +----------+----------+----------+ + | | CLASS A. | CLASS B. | CLASS C. | + +-------------------+----------+----------+----------+ + | 60 feet and less | 100 | 100 | 70 | + | 60 to 100 feet | 90 | 75 | 60 | + | 100 to 200 feet | 75 | 60 | 50 | + | 200 to 400 feet | 60 | 50 | 40 | + +-------------------+----------+----------+----------+ + +Class A includes city and suburban bridges, and those over large +rivers, where great concentration of weight is possible. Class B +denotes highway bridges in manufacturing districts having +well-ballasted roads. Class C refers to ordinary country-road +bridges, where travel is less frequent and lighter. A minority of the +committee modified the table above by making the loads a little +larger. The whole committee agreed in making the load per square foot +less as the span is greater, which is, of course, correct. It would +seem eminently proper to make a difference between a bridge which +carries the continuous and heavy traffic of a large city, and one +which is subjected only to the comparatively light and infrequent +traffic of a country road. At the same time it should not be +forgotten, that, in a large part of the United States, a bridge may +be loaded by ten, fifteen, or even twenty pounds per square foot by +snow and ice alone, and that the very bridges which from their +location we should be apt to make the lightest, are those which would +be most likely to be neglected, and not relieved from a heavy +accumulation of snow. In view of the above, and remembering that a +moving load produces a much greater strain upon a bridge than one +which is at rest, we may be sure, that, as the committee above +referred to recommend, the loads should not be less than those given +in the table. We can easily see that in special cases they should be +more. + +There is another point in regard to loading a highway bridge, which +is to be considered. It often happens that a very heavy load is +carried over such bridges upon a single truck, thus throwing a heavy +and concentrated load upon each point as it passes. Mr. Stoney states +that a wagon with a crank-shaft of the British ship "Hercules," +weighing about forty-five tons, was refused a passage over +Westminster iron bridge, for fear of damage to the structure, and had +to be carried over Waterloo bridge, which is of stone; and he says +that in many cases large boilers, heavy forgings, or castings reach +as high as twelve tons upon a single wheel. The report of the +American Society of Civil Engineers, above referred to, advises that +the floor system be strong enough to carry the following loads upon +four wheels: Class A, 24 tons; Class B, 16 tons; Class C, 8 tons; +though it is stated that these do not include the extraordinary loads +sometimes taken over highways. "This provision for local loads," +says Mr. Boller, one of the committee, "may seem extreme; but the jar +and jolt of heavy, spring-less loads come directly on all parts of +the flooring at successive intervals, and admonish us that any errors +should be on the safe side." + +To pass now to railroad bridges, we find here a very heavy load +coming upon the structure in a sudden, and often very violent, +manner. Experiment and observation both indicate that a rapidly +moving load produces an effect equal to double the same load at rest. +This effect is seen much more upon short bridges, where the moving +load is large in proportion to the weight of the bridge, than upon +long spans, where the weight of the bridge itself is considerable. +The actual load upon a short bridge is also more per foot than upon +a long one, because the locomotive, which is much heavier than an +equal length of cars, may cover the whole of a short span, but only a +part of a longer one. The largest engines in use upon our railroads +weigh from 75,000 to 80,000 pounds on a wheel-base of not over twelve +feet in length, or 2,800 pounds per foot for the whole length of the +engine, and from 20,000 to 24,000 pounds on a single pair of wheels. +The heaviest coal-trains will weigh nearly a ton to the foot, +ordinary freight-trains from 1,600 to 1,800 pounds, and +passenger-trains from 1,000 to 1,200 pounds per foot. Any bridge is +liable to be traversed by two heavy freight-engines followed by a +load of three-quarters of a ton to the foot; so that if we proportion +a bridge to carry 3,000 pounds per foot for the total engine length, +and one ton per foot for the rest of the bridge, bearing in mind +that any one point may be called upon to sustain 24,000 pounds, and +regarding the increase of strain upon short spans due to high speeds, +we have the following loads for different spans exclusive of the +weight of the bridge:-- + + +---------+-----------------+ + | SPAN. | LBS. PER FOOT. | + +---------+-----------------+ + | 12 | 7,000 | + +---------+-----------------+ + | 15 | 6,000 | + +---------+-----------------+ + | 20 | 4,800 | + +---------+-----------------+ + | 25 | 4,000 | + +---------+-----------------+ + | 30 | 3,600 | + +---------+-----------------+ + | 40 | 3,200 | + +---------+-----------------+ + | 50 | 3,000 | + +---------+-----------------+ + | 100 | 2,800 | + +---------+-----------------+ + | 200 | 2,600 | + +---------+-----------------+ + | 300 | 2,500 | + +---------+-----------------+ + | 400 | 2,450 | + +---------+-----------------+ + | 500 | 2,400 | + +---------+-----------------+ + +The above does not vary essentially from the English practice, and is +substantially the same as given by the committee of the American +Society of Civil Engineers. + +The load which any bridge will be required to carry being determined, +and the general plan and dimensions fixed, the several strains upon +the different members follow by a simple process of arithmetic, +leaving to be determined the actual dimensions of the various parts, +a matter which depends upon the power of different kinds of material +to resist different strains. This brings us to the exceedingly +important subject of the nature and strength of materials. + +It has been said that we know what one square inch of iron will hold. +Like the question of loads above examined, this is a matter which has +been settled, at any rate within very narrow limits, by the +experience of many years of both European and American engineers. A +bar of the best wrought-iron an inch square will not break under a +tensile strain of less than sixty thousand pounds. Only a small part +of this, however, is to be used in practice. A bar or beam may be +loaded with a greater weight applied as a permanent or dead-load than +would be safe as a rolling or moving weight. A load may be brought +upon any material in an easy and gradual manner, so as not to damage +it; while the same load could not be suddenly and violently applied +without injury. The margin for safety should be greater with a +material liable to contain hidden defects, than with one which is not +so; and it should be greater with any member of a bridge which is +subjected to several different kinds of strain, than for one which +has to resist only a single form of strain. Respect, also, should be +had to the frequency with which any part is subjected to strain from +a moving load, as this will influence its power of endurance. The +rule in structures having so important an office to perform as +railroad or highway bridges, should be, in all cases, absolute safety +under all conditions. + +The British Board of Trade fixes the greatest strain that shall come +upon the material in a wrought-iron bridge, from the combined weight +of the bridge and load, at 5 tons per square inch of the net section +of the metal. The French practice allows 3-8/10 tons per square inch +of the cross section of the metal, which, considering the amount +taken out by rivet-holes, is substantially the same as the English +allowance. The report of the American Society of Civil Engineers, +above referred to, recommends 10,000 pounds per inch as the maximum +for wrought-iron in tension in railroad bridges. For highway bridges +a unit strain of 15,000 pounds per square inch is often allowed. A +very common clause in a specification is that the _factor of safety_ +shall be four, five, or six, as the case may be, meaning by this that +the actual load shall not exceed one-fourth, one-fifth, or one-sixth +part of the breaking-load. It is a little unfortunate that this term, +factor of safety, has found its way into use just as it has; for it +by no means indicates what is intended, or what it is supposed to. +The true margin for safety is not the difference between the +working-strain and the breaking-strain, but between the +working-strain and that strain which will in any way unfit the +material for use. Now, any material is unfitted for use when it is +so far distorted by overstraining that it cannot recover, or, +technically speaking, when its elastic limit has been exceeded. The +elastic limit of the best grades of iron is just about half the +breaking-weight, or from 25,000 to 30,000 pounds per inch. 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. A +tough and ductile iron should bend double, when cold, without +showing any signs of fracture, and should stretch fifteen per cent of +its length before breaking; but much of the iron used in bridges, +although it may hold 40,000 or 50,000 pounds per inch before failing, +will not bend over 90 degrees without cracking, and has an elastic +limit as low as 18,000 pounds. It is thus full as important to +specify that an iron should have a high elastic limit as that it +should have a high breaking-weight. A specification which allowed no +material to be strained by more than 10,000 pounds per inch, and no +iron to be used with a less elastic limit than 25,000 pounds, would, +at the same time, agree with the standard requirement, both in +England and in the United States, and would also secure a good +quality of iron. + +Two documents published some time since illustrate the preceding +remarks. The first is the account of the tests of the iron taken from +the Tariffville bridge after its failure, and the second is the +specification for bridges on the Cincinnati Southern Railroad. The +Tariffville bridge, though nominally a wooden one, like most +structures of the kind relied entirely upon iron rods to keep the +wood-work together. Although the rods were too small, and seriously +defective in manufacture, the bridge ought not to have fallen from +that cause. The ultimate strength of the iron was not what it should +have been, but yet it was not low enough to explain the disaster; but +when we look at the _quality_ of the iron, we have the cause of the +fall. The rods taken from the bridge show an ultimate tensile +strength of 47,560 pounds per inch, but an elastic limit of only +19,000 pounds; while the strain which was at any time liable to come +on them was 22,000 pounds per inch, or 3,000 pounds more than the +elastic limit. The fracture of the tested rods, which, it is stated, +broke with a single blow of the hammer very much in the manner of +cast-iron, showed a very inferior quality of metal. The rods broke in +the bridge exactly where we should look for the failure; viz., in the +screw at the end. No ordinary inspection would have detected this +weakness. No inspection _did_ detect it, but a proper specification +faithfully carried out would have prevented the disaster. + +Look now at an extract from the specification for bridges upon the +Cincinnati Southern Railway:-- + +"All parts of the bridges and trestleworks must be proportioned to +sustain the passage of the following rolling-load at a speed of not +less than 30 miles an hour: viz., two locomotives coupled, each +weighing 36 tons on the drivers in a space of 12 feet, the total +weight of each engine and tender loaded being 66 tons in a space of +50 feet, and followed by loaded cars weighing 20 tons each in a space +of 22 feet. An addition of 25 per cent will be made to the strains +produced by the rolling-load considered as static in all parts which +are liable to be thrown suddenly under strain by the passage of a +rapidly moving load. A similar addition of 50 per cent will be made +to the strain on suspension links and riveted connections of +stringers with floor-beams, and floor-beams with trusses. The +iron-work shall be so proportioned that the weight of the structure, +together with the above specified rolling-load, shall in no part +cause a tensile strain of more than 10,000 pounds per square inch of +sectional area. Iron used under tensile strain shall be tough, +ductile, of uniform quality, and capable of sustaining not less than +50,000 pounds per square inch of sectional area without fracture, and +25,000 pounds per square inch without taking a permanent set. The +reduction of area at the breaking-point shall average 25 per cent, +and the elongation 15 per cent. When cold, the iron must bend, +without sign of fracture, from 90 to 180 degrees." + +A specification like this, properly carried out, would put an +absolute stop to the building of such structures as the Tariffville +Bridge, and would prevent a very large part of the catastrophes which +so often shock the community, and shake the public faith in iron +bridges. Reference has been made above to the proper loads to be +placed upon wrought-iron when under a tensile strain. Similar loads +have been determined for other materials, and for other kinds of +strain. + +The preceding remarks in regard to the loads for which bridges should +be designed, and the safe weight to be put upon the material, are +given to show how far the safety of a bridge is a matter of fact, and +how far a matter of opinion. It will be seen that the limits within +which we are at liberty to vary, are quite narrow, so that +bridge-building may correctly be called a science; and there is no +excuse for the person who guesses, either at the load which a bridge +should be designed to bear, or at the size of the different members +of the structure. Still less can we excuse the man who not only +guesses, but who, in order to build cheaply, persistently guesses on +the wrong side. + +It will, of course, be understood, when it is said that +bridge-building may be called a science, that it can only be so when +in the hands of an engineer whose judgment has been matured by wide +experience, and who understands that no mechanical philosophy can be +applied to practice which is not subject to the contingencies of +workmanship. There are many bridges which will stand the test of +figures very well, and which are nevertheless very poor structures. +The general plan of a bridge may be good, the computations all right, +and yet it may break down under the first train that passes over it. +There are many practical considerations that cannot be, at any rate +have not yet been, reduced to figures. It is not enough that the +strains upon each member of a bridge should be correctly estimated, +and fall within the safe limits: the different members of the bridge +must be so connected, and the mechanical details such, as to insure, +under all conditions, the assumed action of the several parts. In +fine, while we can say that a bridge that does not stand the test of +arithmetic is a bad bridge, we cannot always say that a structure +which does stand such a test is a good one. + +We often hear it argued that a bridge must be safe, since it has been +submitted to a heavy load, and did not break down. Such a test means +absolutely nothing. It does not even show that the bridge will bear +the same load again, much less does it show that it has the proper +margin for safety. It simply shows that it did not break down at that +time. Every rotten, worn-out, and defective bridge that ever fell has +been submitted to exactly that test. More than this, it has +repeatedly happened that a heavy train has passed over a bridge in +apparent safety, while a much lighter one passing directly afterwards +has gone through. In almost all such cases, the structure has been +weak and defective; and finally some heavy load passes over, and +cripples the bridge, so that the next load produces a disaster. For +the test of a bridge to be in any way satisfactory, we must know just +what effect such test has had upon the structure. We do not find this +out by simply standing near, and noting that the bridge did not +break down. We must satisfy ourselves beyond all question that no +part has been overstrained. + +A short time ago the builders of a wretchedly cheap and unsafe +highway bridge, in order to quiet a fear which had arisen that the +structure was not altogether sound, tested a span 122 feet long with +a load of 58,000 pounds; and inasmuch as the bridge did not break +down under this load, which was less than a quarter part of what it +was warranted to carry safely, the county commissioners considered +the result eminently satisfactory, and remarked that the test was +made merely to satisfy the public that the bridge was abundantly safe +for all practical uses. The public would, no doubt, have been +satisfied that the Ashtabula bridge was abundantly safe for all +practical uses had it stood on that bridge in the morning and seen a +heavy freight-train go over it, and yet that very bridge broke down +directly afterwards under a passenger-train. + +Now, according to the common notion, that was a good bridge in the +morning, and a very bad bridge, or rather, no bridge at all, in the +evening. The question for the public is, When did it cease to be a +good bridge, and begin to be a bad one? A test like the one referred +to above can do no more than illustrate the ignorance or lack of +honesty of those who make it, or those who are satisfied with it. +Such a test might come within a dozen pounds of breaking the bridge +down, and no one be the wiser. The entire absurdity of such testing +has recently been illustrated in the most decided manner. The very +same company that built the bridge above referred to, made also +another one on exactly the same plan, and of almost precisely the +same size, and tested it when done by placing almost exactly the same +load upon it. The bridge did not break down; and the county +commissioners, for whom the work was done, were satisfied that it was +"abundantly safe for all practical uses," accepted it, paid for it; +and in less than ten years it broke down under a single team and a +little snow, weighing in all not over one-tenth part of the load the +bridge was warranted to carry, and not over one-half the load with +which it had been previously tested. If this bridge had been "tested" +by five minutes of honest arithmetic, it would have been promptly +condemned the very day it was finished. + +In view of the preceding, what shall we say of a bridge company that +deliberately builds a bridge in the middle of a large town, where it +will be subjected to heavy teaming, and, owing to its peculiar +location, to heavy crowds, and warrants to the town that it shall +safely hold a ton per running-foot, when the very simplest +computation shows beyond chance of dispute that such a load will +strain the iron to 40,000 pounds per square inch? We are to say, +either that such a company is so ignorant that it does not know the +difference between a good bridge and a bad one, or else so wicked as +to knowingly subject the public to a wretchedly unsafe bridge. The +case referred to is not an imaginary one, but existed recently in the +main street of a large New-England town. The joints in that bridge, +which could safely hold but 20,000 pounds, were required to hold +60,000 pounds under the load which the builders had warranted the +bridge to carry safely. The case was so bad, that, after a lengthy +controversy, the town officers had a thorough expert examination of +the bridge, which promptly condemned it as in imminent danger of +falling, and as having a factor of safety of only 1-15/100, which is +practically no factor at all. Notwithstanding all this, and in the +face of the report, the president of the bridge company came out with +a letter in the papers, in which he pronounced the bridge "perfectly +safe." Thus we actually have the president of a bridge company in +this country stating openly that a factor of safety of 1-15/100 makes +a bridge perfectly safe, or, in other words, that a bridge can safely +bear the load that will break it down, for he very wisely made not +the slightest attempt to disprove any of the conclusions of the +commission; and this company has built hundreds of highway bridges +all over the United States, and is building them to-day wherever it +can find town or county officers ignorant enough to buy them. + +It might be supposed, that, under the above condemnation, the +authorities controlling the bridge would have taken some steps to +prevent the coming disaster. They did, however, nothing of the kind, +but allowed the public to travel over it for more than a year, at the +most fearful risk, until public indignation became so strong that a +special town-meeting was called, and a committee appointed to remove +the old bridge, and to build a new one. + +One of the worst cases of utterly dishonest bridge-building that we +have had of late years in Massachusetts, was that of the iron highway +bridge across the Merrimac River at Groveland, a few miles below +Haverhill, one span of which broke down in January, 1881. This bridge +was built in 1871-1872, and consisted of 6 spans, each about 125 feet +long. The whole cost of the structure was $80,000, and the contract +price for the iron-work was $28,000. The company which made that +bridge, agreed in their contract to give the county a structure that +should carry safely 3,000 pounds per running-foot besides its own +weight; but they built a bridge, which, if they knew enough to +compute its strength at all, they knew perfectly well could not +safely carry over one-quarter part of that load. In fact, the weight +of the bridge alone is more than it ever ought to have borne. The +company warranted each span of that bridge to carry safely a net or +moving load of 165 tons, and it broke down under a single team and a +small amount of snow. The company warranted that bridge to carry +safely a load which would strain the iron to 50,000 pounds per inch, +when it knew perfectly well that 15,000 pounds per inch was the most +that could safely be borne. + +There are several concerns in the United States which make a +specialty of highway bridges, and which, taking advantage of the +ignorance of public officials, are flooding the country with bridges +no better than that at Groveland. On an average, at least twenty of +these miserable traps tumble down every year, and nothing is done to +bring the guilty parties to punishment. Dishonest builders cheat +ignorant officials, and the public suffers the damage and pays the +bills. Is human life worth enough to pay for having these structures +inspected, and, if found unsafe, strengthened or removed? Can we do +any thing to prevent towns and counties from being imposed upon by +dishonest builders? We certainly can, if those who control these +matters care enough about it to do it. There are two ways of buying a +bridge,--a good way and a bad one; and these two ways are so plain +that no one can misunderstand. To buy a bad bridge, just as soon as +your town or county votes money for a new bridge, certain agents--and +they are as numerous as the agents for sewing-machines or +lightning-rods--will call on, or write to, the town or county +officers, and will offer to build any thing under heavens you want of +any size, shape, or material, and for almost any price. They will +produce testimonials from all the town and county officers in the +country for the excellence of their bridges, and would not hesitate +to give reference, even, for their moral character, if you should ask +it. If they find that you don't know any thing about bridges, they +will, to save you the trouble, furnish a printed specification; which +document will commit you to pay the money, but will not commit the +bridge company to any thing at all. When the bridge is put up, you +never will know whether the iron is good or bad, nor whether the +dimensions and proportions are such as to be safe or not. You will +know that you have paid your money away, but you never will know what +you have got for it until some day when your bridge gets a crowd upon +it, and breaks down, and you have the damage to pay. This mode of +buying a bridge is very common. To buy a good bridge, first determine +precisely what you want; and if you don't know any thing in regard to +bridge-building yourself, employ an engineer who does, to make a +specification stating exactly what you want, and what you mean to +have. Then advertise for bridge-builders to send in plans and +proposals. Let the contractors understand that all plans and +computations are to be submitted to your engineer, that all materials +and workmanship will be submitted to your inspectors, and that the +whole structure is to be made subject to the supervision of a +competent engineer, and accepted by him for you. You will find at +once, that, under such conditions, all travelling agents and builders +of cheap bridges will avoid you as a thief does the light of day. You +will have genuine proposals from responsible companies, and their +bids should be submitted to your engineer. When you have made your +choice, let the contract be written by your lawyer, and have the +plans and specifications attached. Employ a competent engineer to +inspect the work as it goes on; and when it is done, you will have a +bridge which will be warranted absolutely sound by the best +authority. This mode of buying a bridge is very uncommon. + +The Ashtabula bridge, it is stated in the report of the committee of +the Ohio Legislature appointed to investigate that disaster, had +factors,--we can hardly call them factors of safety,--in some parts +as low as 1-6/10 and 1-2/10, such factors referring to the +breaking-weight; and even these factors were obtained by assuming the +load as at rest, and making no allowance for the jar and shock from a +railroad train in motion. Well may the commissioners say, as they do +at the end of their report, "The bridge was liable to go down at any +time during the last ten years under the loads that might at any time +be brought upon it in the ordinary course of the company's business, +and it is most remarkable that it did not sooner occur." + +One point always brought forward when an iron bridge breaks down, is +the supposed deterioration of iron under repeated straining; and we +are gravely told that after a while all iron loses its fibre, and +becomes crystalline. This is one of the "mysteries" which some +persons conjure up at tolerably regular intervals to cover their +ignorance. 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. The +Niagara-Falls railroad suspension bridge was carefully inspected +after twenty-five years of continued use under frequent and heavy +trains, and not only was it impossible to detect by the severest +tests any defect in the wire of the cables, but a piece of it, being +thrown upon the floor, curled up, showing the old "kink" which the +iron had when it was first made, and wound on the reel. The Menai +suspension bridge, in which 1,000 tons of iron have hung suspended +across an opening of 600 feet for sixty years, shows no depreciation +that the most rigid inspection could detect. Iron rods, recently +taken from an old bridge in this country, have been carefully tested +after sixty years of use, and found to have lost nothing, either of +the original breaking-strength, or of the original elasticity. + +The question is frequently asked, Does not extreme cold weaken iron +bridges? 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. Iron containing phosphorus is "cold-short," or +brittle when cold, and will break quicker under repeated and sudden +shocks in cold weather than when it is warm. With good iron, properly +used, we need have no fear on this point. The securing such iron is a +matter to which the utmost attention is paid by our first-class +bridge-building firms, but it is a matter to which no attention is +paid by the builders of cheap bridges. We might suppose that a +person, in putting an insufficient amount of iron into a bridge, +would be careful to get the best quality; but exactly the reverse +seems to be the case, on the ground, perhaps, that the less of a bad +thing we have, the better. + +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. There are, without the slightest +question, hundreds of bridges now in use in this country, which, as +far as mere proportions and dimensions go, would appear to be +entirely safe, but which, on account of the quality of the iron with +which they are made, are entirely unsafe; and there always will be, +as long as public officials purchase iron which they know nothing +about, to put into bridges. When a bridge is finished, the ordinary +examinations never detect the quality of the iron; so that the wise +remarks of many inspectors, or the opinions of those in charge of +these structures, as to the exact condition of a bridge, are of +little or no value. + +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 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; while, however good our timber may be in the beginning, we +never can be entirely sure of its condition afterwards. There are +wooden bridges now standing in this country, all the way from sixty +to eighty years old, which are apparently as good as ever; while +there are others, not ten years old, which are so rotten as to be +unfit for use. It will not do to assume, that, because no defects are +very evident in a wooden bridge, therefore it has none. When a wooden +bridge, originally made of only fair material, has been in use under +railroad trains for twenty-five or thirty years, and in a position +where timber would naturally decay, we are bound to suspect that +bridge. To assume such a bridge to be all right until we can prove it +to be all wrong, is not safe. To assume a bridge to be all wrong +until we can prove it to be all right, is a safe method, though not a +popular one. Any person who has had occasion to remove old wooden +bridges, will recall how often they look very much worse than was +anticipated. + +There is one defect in railway bridges which has often led to the +most fearful disasters, and which, without the slightest question, +can be almost entirely, if not entirely, removed, and at a moderate +cost. At least half the most disastrous failures of railroad bridges +in the United States have been due to a defective system of +flooring. With a very large proportion of our bridges, the failure +of a rail, the breaking of an axle, or any thing which shall throw +the train from the track, is almost sure to be followed by the +breaking down of the bridge. The cross-ties are in many cases very +short, and the floor is proportioned for a train _on_ and not _off_ +the rails. When an engine on such a floor leaves the track, it +plunges off the ends of the cross-ties into the open space between +the stringers and the chords, and generally wrecks the bridge. To +prevent this, the cross-ties should be long and well supported, and +placed so close that a derailed engine cannot cut through them. The +track should also be provided with guard-timbers well fastened, and +the width between the trusses should be so great that the wheels of a +derailed train will be stopped by the guard-rail before the side of +the widest car can strike the truss. + +The importance of a substantial floor system has been very fully +recognized by the railroad commissioners of Massachusetts, who have +recently issued a very suggestive circular, accompanied by numerous +examples of track construction for railway bridges. If this circular +receives proper attention, it is sure to produce good results. + +Another point which has often been neglected, is making sufficient +provision to resist the force of the wind. A tornado, such as is not +uncommon in this country, will exert a force of 40 pounds per square +foot, which upon the side of a wooden bridge, say of 200 feet span, +and 25 feet high, and boarded up as many bridges are, would amount to +a lateral thrust of no less than 100 tons; and this load would be +applied in the worst possible manner, i.e., in a series of shocks. +There have been many cases in this country where bridges have been +blown down; and a case recently occurred where an iron railroad +bridge of 180 feet span, and 30 feet high, and presenting apparently +almost no surface to the wind, was blown so much out of line that the +track had to be shifted. The recent terrible disaster at the Firth of +Tay was, no doubt, due to this cause. + +At the time of the Tariffville catastrophe, it was gravely stated at +the coroner's inquest, and by railroad officers who claimed to know +about such things, that the disaster was caused by the tremendous +weight of two locomotives which were coupled together, and it was +stated that one engine would have passed in safety; and directly +afterwards the superintendent of a prominent railroad in New England +issued an order forbidding two engines connected to pass over any +iron bridges. It is all very well for a company to issue such an +order, so far as it may give the public to understand that it is +determined to use every precaution against disaster; but such an +order may have the effect of creating a distrust which really ought +not to exist. If a railway bridge is not entirely safe for two +engines, it is certainly entirely unsafe for one engine and the train +following; the only saving in weight by taking off one engine being +the difference between the weight of that engine and the weight of +the cars that would occupy the same room. For example, a bridge of +200 feet span will weigh 1,500 pounds per lineal foot. An engine and +its tender will weigh 60 tons in a length of 50 feet, and a loaded +freight-train may easily weigh 2/3 of a ton per lineal foot. The +total weight of the span, with two engines, and the rest of the +bridge covered with loaded freight-cars, would thus be 320 tons. If +we take off one engine, and fill its place with cars, we take off 60 +tons, and put in its place 33 tons; i.e., we remove 27 tons, or just +about 1/12 of the working-load. Taking off a large part of the +working-load, however, is taking off a very small part of the +breaking-load; with a factor of safety of six, for example, taking +off 1/12 of the working-load is taking off less than 1/70 of the +breaking-load. An order, therefore, like that above, can only be of +use when the working-load and the breaking-load are so nearly alike +that the actual load is a dangerous one: that is when the bridge is +unfit for any traffic whatever; so that, if such an order was really +needed, it would, in itself, be, in the eyes of an engineer, a +condemnation of the bridge. + +Having seen something of the structures which require inspecting, let +us now see what kind of inspection we have in this country, and the +result of it; and let us also see the inspection which we might have, +and the results that might be produced. Looking first at railroad +bridges, it might be supposed that no one could be so much interested +in keeping such structures in good order as the companies which own +those bridges, and which have the bills to pay in case of disaster. +This is, of course, so; but, in spite of the fact, the Ashtabula +bridge broke down, on one of the best managed lines in the country, +and cost the company over half a million dollars in damages. No +railroad bridge ever broke down, which the owners were not interested +in keeping safe; but there is always a desire to put off incurring +large expenses until the last moment, and thus weak bridges are very +often let go too long. A short time since, the superintendent of a +large railroad stated plainly before a legislative committee, that +many of the smaller roads were not safe to run over, but that such +roads were having a hard time, and could not afford to keep their +track and bridges in a safe condition. During the past ten years over +two hundred railroad bridges in the United States have broken down. +These bridges were all kept under such inspection as the railroad +companies owning them considered sufficient, or such as they could +afford; but either the supervision was defective, or the companies +knowingly continued the use of unsafe bridges, and this fault has by +no means been confined to the smaller and poorer roads. It would +seem, therefore, that inspection by the companies themselves has not +been sufficient. It certainly has not been enough to prevent two +hundred disasters in ten years. It is the custom in several of the +United States to maintain what is termed a railroad commission. The +original intention seems to have been for these commissions to keep +the railroads under some kind of inspection, and in some way to +assist in settling any questions that might arise between different +companies, and between railroad companies and the public. As far as +we can judge by the results produced, in the States where these +commissions have been established, we can hardly pronounce them of +any very great importance. In many States, it is very certain, that, +in regard to matters of inspection, the work of these boards has been +simply a farce; and it could hardly be otherwise in a State which +pays its commissioners only $1,000 salary, or, worse yet, as in some +cases, only $500. Add to this, that in many cases the appointments +have been purely political ones, and we can see the absurdity of +expecting any results of value. We should hardly suppose that three +men, in many cases entirely unacquainted with mechanical matters, +could by riding over a railroad once or twice a year, occasionally +getting out to examine the paint on the outside of the boards, which +conceal a truss from view, judge very correctly of the elastic limit +of the iron rods which they have never seen, and of which they do +not even know the existence. + +For ample proof of the utter inefficiency of the present system, we +have only to compare the reports of the railroad commissioners in +almost any State, with the actual condition of the structures +described. 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. + +There is, in fact, no difference which any ordinary inspection would +detect between these bridges as they stand to-day, and the +Tariffville bridge as it stood the day before it fell. In another +State, an iron bridge is in use under heavy trains, which has a +factor of only 2-1/2 instead of 6, and yet the State report +pronounces it an excellent structure and a credit to the railroad +company, which recklessly allows its trains to pass over it. In yet +another State, the commissioners in 1874 reported that a certain +bridge should be removed; and this was quite correct, as it was an +eminently unsafe bridge. In 1875 they suggested the same thing again. +In 1876 they say, "This bridge must be rebuilt the coming spring." In +1877 they again reported, "This bridge must be rebuilt before the +spring opens. It is old, and will not be safe for the passage of +trains over it, if the ice or freshet should take away the temporary +trestles, which now in a great measure support the truss." + +A year later than that, in 1878, a public protest was made against +the further use of that bridge, as the lower chords were rotten, +broken, pulled apart, and the only thing that held it up was a +trestle, liable at any time to be knocked out by the ice; and yet, +after all this, in reply to the protest, the commissioners replied +that they had just "tested" the bridge by running an engine over it, +and pronounced it "safe for the present," whatever that may mean. +Now, just how it was that this bridge, which was old, rotten, and +worn out, which the commissioners themselves had condemned for four +successive years, which they had said two years before must be +rebuilt the coming spring, and which relied entirely upon a trestle +liable at any time to be carried away, had suddenly become "safe for +the present," is not plain to see. + +Evidently such inspection as this is of no value. It is exactly this +utterly incompetent and dishonest inspection, this guessing that a +bridge will stand until it falls, that lies at the bottom of half the +disasters in the country. It is under exactly such inspection that +those wretched traps, the Ashtabula and Tariffville bridges, fell, +and killed over one hundred people. No wonder that railroad officials +have an undisguised contempt for State inspection. While in a few +States the inspection is not quite so bad as that referred to, as a +general thing it is no better; and we have no right to expect any +thing better under the present system. The State inspection which we +have had throughout this country has not prevented the breaking down +of one hundred bridges in the past ten years. Twenty-five States have +railroad commissions; but in nine of them the commission consists of +only a single man, who, in some cases, is paid only $500 a year. A +State can pay $500 a year for having its bridges inspected, and it +will get such service as never did and never will prevent a disaster; +or it can pay a good price for competent inspection, which will be +worth ten times the money to the State. The money which the Lake +Shore Railroad paid in damages for the Ashtabula disaster alone, +would have employed permanently six men at $5,000 a year each, and a +hundred lives would have been saved besides. + +With regard to highway bridges, we are, if possible, even worse off +than in regard to railway bridges; for in the case of such +structures, neither the owners nor the State make any pretence at +inspection. It is impossible to say how many highway bridges have +broken down during the past ten years, but it is estimated by +bridge-builders that the number cannot be less than two hundred. This +is, no doubt, far within the truth; and by far the larger part of +these structures are not old wooden bridges, but are new bridges of +iron. + +If we knew positively that in just six months a terrible disaster +would occur under the present system of bridge inspection, and knew +also, that, by a better system, such disaster would certainly be +prevented, it is possible that a change might be made. We know that +a proper method of building and inspecting bridges would certainly +have prevented the disasters at Ashtabula, Tariffville, and Dixon. We +know that the inspection which those bridges received, did not +prevent three of the most fearful disasters the country has ever +seen. Admitting, now, that structures so important to the public +safety as bridges, both upon roads and railroads, ought to be kept +under rigid inspection and control, and that no system at present +existing has been able to prevent the most fearful catastrophes, what +shall we do? Directly after the Ashtabula disaster, the Ohio +legislative committee, appointed to investigate that affair, +presented to the Legislature a bill, "To secure greater safety for +public travel over bridges," in which was plainly specified the loads +for which all bridges should be proportioned, the maximum strains to +which the iron should be subjected, and a method for inspecting the +plans of all bridges before building, and the bridges themselves +during and after construction. The governor, with the consent of the +Senate, was to appoint the inspector for a term of five years at a +salary not exceeding $3,000 a year, such inspector to pass a +satisfactory examination before a committee of the American Society +of Civil Engineers, themselves practical experts in bridge +construction, and he was also to take a suitable oath for the +faithful performance of his duty. This bill never became a law. An +appropriation was made for a short time to pay for certain +examinations, and there the matter stopped. + +The committee of the American Society of Engineers were not agreed +upon this matter. Messrs. James B. Eads and Charles Shaler Smith +suggested the appointment in each State of an expert, to whom all +plans should be submitted, and by whom all work should be +inspected,--such expert to have been examined and approved by the +American Society of Civil Engineers. The inspector was also to visit +the scene of every accident, so called, and to ascertain, as far as +possible, the cause. Messrs. T. C. Clarke and Julius W. Adams +believed, that, in the present state of public opinion, the above +method would be impracticable, and feared, that, if inspectors were +appointed, it would be by political influence, and that the result +would be worse than at present, as the inspectors would be +inefficient, and yet, to a great extent, would relieve the owners of +bad bridges from legal responsibility. They held that the best that +could be done would be to provide means, in case of disaster, to fix +plainly the responsibility, and recommended, First, that the standard +for strength fixed by the Society should be the legal standard; and, +in case it should be found that any bridge was of less strength than +this, it should be taken as _prima facie_ evidence of neglect on the +part of the owners. Second, that no bridge should be opened to the +public until a plan giving all dimensions, strains, and loads, sworn +to by the designers and makers, and attested by the corporation +having control of it, had been deposited with the American Society; +and further, that the principal pieces of iron in the bridge should +be stamped with the name of the maker, place of manufacture, and +date. Messrs. A. P. Boller and Charles Macdonald looked rather toward +effecting the desired result by so directing public sentiment by +keeping the correct standard for bridges before it, that it would +eventually compel the passage of the necessary laws. + +Whether it is possible, in this country, to make an appointment +dependent purely upon honesty and capacity, and free from political +influence, may well be doubted. No competent engineer would be +willing to accept a position which would place upon him so great a +responsibility, except under a very carefully devised plan. A very +considerable force of inspectors would be required to carry out a +system which should produce the desired result. The amount of work +to be done at the commencement would be very great, as no proper +inspection has ever been made of the greater part of the bridges in +the country, of which the number is very large. If any such plan as +above suggested should be found feasible, the inspectors should have +in their possession a complete set of plans of every bridge of +importance in the State, with all the computations of its strength, +and as complete a history of each structure from its commencement as +can be made up, all this to be supplemented by periodic examinations. +If, from such records, we find that a bridge was made of ordinary +green timber twenty-five years ago, and that it has been getting +rotten ever since; that it has rods of common merchant iron that were +bought by some person, not specially acquainted with the business, +from an unknown firm,--we had better pull it down before it falls. +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. + +Such a record would be the property of the State, always accessible +to any one, and would be handed down, so that the knowledge of one +person would not expire with his term of office. No bridge should be +erected in any State without first submitting the plans to the +inspector, and receiving his approval, and depositing with him a +complete set of the plans and computations for the work. By this +approval is not meant that the inspector is merely to give a +favorable opinion as to the plan, but that he is to find, as a matter +of fact, whether the proposed dimensions and proportions are such as +will make a safe bridge--and just what a safe bridge is, can be +plainly defined by law, as it is in Europe, and as it has been +proposed by the American Society of Civil Engineers. For example, if +the law says that an iron railway bridge of 100 feet span shall be +proportioned to carry a load of 3,000 pounds per lineal foot besides +its own weight, and that, with such a load, no part shall be strained +by more than 10,000 pounds per inch, all the inspector has to do is +to go over the figures, and see that the dimensions given on the plan +are such as will enable the bridge to carry the load without +exceeding the specified strains. When the work is erected, the +inspection must show that the plan has been exactly carried out, that +the details are good, and proper evidence of the quality of the +material used should also be given. Such inspection as this would at +once prevent the erection of bridges like those at Ashtabula and +Tariffville, and would save the public from such traps as those that +fell at Dixon and at Groveland. Perhaps the most difficult thing to +do will be to get satisfactory evidence in regard to the bridges that +have been for a considerable time in use, and of which we do not know +the history. This will be especially true in regard to the wooden +bridges, of which there are so many about the country. Not only is it +very difficult to be sure of the exact condition of the timber, but +it is equally hard to tell any thing about the iron. The Tariffville +bridge fell on account of defective iron, and the defect was of such +a nature as to defy any ordinary inspection. 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. + +Of course we cannot expect to get a perfect system all at once. Any +plan which might be proposed would, no doubt, be found more or less +defective at first. We can hardly get a system worse than the one we +now have, which allows forty bridges to break down every year. We may +get a better one. To make the public see the need of such a system is +the first step to be taken. + + * * * * * + +LEE AND SHEPARD'S POPULAR HANDBOOKS. + +Price, each, in cloth, 50 cents, except when other price is given. + + +Forgotten Meanings; or an Hour with a Dictionary. By ALFRED WAITES, +author of Historical Student's Manual. + +Handbook of Elocution Simplified. By WALTER K. FOBES, with an +Introduction by GEORGE M. 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