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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    |
