New Orleans Republican. [volume] (New Orleans, La) 1867-1878, 1875-02-26

support"
After May, 1868, matters went smooth.
for . time. The skilled assistants of MI
Eads calculated to nicely the dimension
Of every piece required in the bridge. Hi
craftsmen made working drawings and
his skilled contractors, from these pre-
pared in the shop the various castings and
forgings required. The piers were go
ready and partial suspension bridg,
built for erecting the arches. 1t has beez
stated before how quietly this was all done
60 that the river interest could not TAXI
alarm until it was too late to do more thar
enter protest. The board Of engineers
made its sever to- be-ridiculed report, and
last fourth of July, with grand Mard
Gras display, the bridge was opened t.
traffic.
This little patch of history brings Us te
the supposed completion of the bridge and
appropriately introduces considerat ion Of
what has been developed since. The
bridge ID now on trial. We are to judge
of the ability Of it's builder by compar ison
of the results anticipated with those &C
tually obtained.
We have shown that Mr. Eads considered
it at the outset most economical plan, and
that it has proven excessively expensive;
therefore, on this point, his judgmen was
defective. 1t is justly considered serious
matter in estimating for bridge to under
estimate, by over two thirds. the final cost
The superstition that. the bridge wO uld be a
beautiful structure, we'll calculated to adorn
the handsome river fronts of East and West
St. Louis was correct, as shown by the large
sized, tinted engraving that has been sent
down to us for our delec tation. For this
due credit should be given both builder and
engrsver.
Next after cost and beauty comes the
question of safety. There seems some rea-
bridge. 1t is stated that passenger trains
are not allowed to cross it, but that con.
nection between the railroad depots Of
East and West St. Louis, for passeng ers, is
made by running omnlbuses over the
bridge, and that to make connection in
VuAo way t0hCo u WACA AOuSCA tAlAO IAdu
was required by the ferry route in old
times. We may find some explana ton of
this in the published transactions of the
American Society of Civil Engineers, vol.
ume three, No. 6-another paper not in
general circulation.
In this number is printed an essay from
Mr.. James B. Eads, in support Of the propo
sition that upright arohed bridges can be
more economically constructed than is
possible by any other method whatever,
no matter what length of span may be re-
quired." In the paper Mr.. Eads practically
abandons the upright arch," and substi-
tutes what lie really "bow-string girder,"
but which he assumes to be an upright
arch. Some extracts from the discussion
this paper provoked will answer our pur:
pose.
We first present extracts from the re-
marks of Mr.. Samuel H. Shreve, as follows:
The paper before the society appears to
be an acknowledgment of the 'disadvan-
tages of the system adopted fOl the super
structure Of the ST. Louis bridge" which
the writer says were forcibly thrust upon
his attention in the progress of that work
He says OF the bridge: "If the effects of
temperature could be avoided, and the
curve were parabola, an equally distrib-
uted load on q rib would, of course. be
borne by the upper and lower tubes equally,
that il, half on each" but the effects of
the temperature are inevitable, aud conse-
quently the above supposition, il correct
(which it is not,. is without value. He
further says: "Tnis extension from the
temperature) causes the crown to rise,
which relieves the lower tube of compress
sion at the abutments, and hence that tube
does not then support any portion of the
weight Of the rib or the load.
At the crown the strains are likewise
changed. There, however, the lo,cer tube
does all the duty, as the upward bending
of the rib relaxes the compression in the
upper tube at this point"
Suppose the crown to rise, the lower tube
If relievd OF compression at the abutmeRts
would not he strained at any point. Brac
ing beneath parabOlic arch Uniformly
loaded can receive no strain and is useless,
and if the curve of the tube considered is
not parabola, it is SO near it, that the
strains which are transferred by the braces
to the lower tube are too small to be
noticed.
The conclusion is unavoidable, that the
upper tube at times must bear the whole
load, and even more, for the tubes "are
rigidly held to the abutments by anchor
bolts" and large extra amount Of strain is
in this manner brought upon the loaded
tube. Now consider the opposite condition:
"As the ribs are formed for a medium
temperature, contraction by cold reverses
these strains-the crown Of the arch falls"
and the lower tube must just as surely take
the whole load and the upper one be use
less One may. and probably does,
expand or contract more than the other,
and the condition is still worse.
The result is simply this: Each tube must |
contain quantity of material sufficient TO
resist the strains caused by full load, and
more ION account Of the boiling down of |
the abut,nentsl, or be injuricusiy strained.
This doubt as to which members the |
strains will affect should not exist il re
gard to any truss. and the axiom may be laid |
down, that plan in which such ambiguity |
Of strains obtains. is sufficiently defective |
to be rejected without. further examina-
The form Of arch which the writer now |
recommends is certainly grea. advance
upon his previous one, but it is doubtful If |
it possesses great advantages over an ordi- |
nary bowstring. His views, in this partic |
uIar seem rather extreme, and will hardly |
be accepted by engineers who are likely to
be satisfied. for the present generation, at
least, with what has already been done in
the construction of steel arches.
From these remarks we naturally draw
the inference, as newspaper engineers,
that Mr.. Eads might, on the side of econo-
nv, have dispensed with one-haif OF his
steel arches, since it appears that only in
cases more than one-haif Of his
arches bear any load likely to be placed
upon the bridge, while in other cases the
arches acting have to bear the weight of