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bridge, originally made of only fair material, has been in use under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.
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