, 1889-12-01
AMERICAN BRIDGES.
What Several Famous French Engineer.
Have to SAY About Them.

VIM ocNcrhA 6nmou1 french engineer
Have to Say About Them.
The Societe des Ingenieurs Civils re-
Gently discussed this question, and on
account of this discussion, published
in The Revue Industrielle, may be of
interest, as showing what foreign en-
gineers think of American methods:
The new systems. of construction en-
ployed in America for metallic bridges
are well known. One of the most no
ticeable bridges is that at Poughkeep-
sic, on the Hudson, which was opened
last year. Rivets are very sparingly
used, large pins being substituted,
thus rendering the erection of the
trusses more economical and rapid.
The metallic portion of the large
bridge at Poughkeepsie was erected In
a few months. Mr.. f. de Gazay men
tons, in a communication which he
has just made to the Societe DIES In
genieurs Owls, a still more extraordi-
nary example. The large bridge at
the base of Niagara Falls is 200 feet
above the river, with central spans,
4SO feet long, of the same system as
those used in the bridge over the Hud.
son. The shop work and erection of
Niagara bridge were completed in the
short space of nine months and a half.
The dimensions of the ~Poughkeepsie
bridge are given, followed by the
statement that this work was erected
very rapidly and economically, not
w~ithstanding its magnitude. Four of
the spans are rigid trusses, which were
erected upon false work resting on
enormous piles driven into the bed of
the river near its center. The three
remaining spans were erected without
scaffolding or other false work, &C
cording to the new system called by
the Americans "cantilever."
To illustrate the great economy and
safety resulting from the simplicity of
he American system, the author re
calls the facts which occurred a few
years ago Oh the Oroya railroad, which
crosses the Cordilleras at an alti
tude of more than 12, 600 feet.
AT the Verrugas viaduct, three short
spans on the Fink system, 100 feet
long, were erected in sixteen hours by
a force of fifty men at a height of 275
feet above the ground. On the same
railroad, four spans, each 100 feet in
length, were erected. Two were built
by the English, with the old American
Town truss. The erection required
more than two months. When tested
the first one fell into the ravine. The
second also broke down, when loaded.
and fell upon the scaffolding which
had been left in place. The third
bridge, of French construction, and
whose lattice trusses were riveted,
was erected in about a month, and
sustained the test perfectly. The
fourth, of American construction, on
the Fink system, also sustained the
test without injury. 1t had been
erected in five days. An interesting
fact to be noted is that the three Euro
pean bridges weighed 1854 tons, while
the American bridge only weighed
sixty-six tons. These four bridges
were of iron, and their prices must
necessarily have been in proportion to
their weights, apart from certain diff
ferences in the method of construc-
ton.
After the reading of this communi-
cation, Mr.. 8. Perisse expressed the
opinion that, when the question of
time is a condition sine qua non, it
is well to use American pinned
bridges; but that in all other cases the
preference should be given TO riveted
bridges. Even though pinned bridges
sustain tests just as well as riveted
bridges, there is reason to believe that
the latter will be more durable, since
the play which necessarily occurs be-
tween the pins and the holes is a sure
cause of destruction that does not exist
in riveted bridges.
On the other hand, to compare the
economy of one system with that of
the other, account should be taken
not only of the weight, but also of the
cost of construction per unit of
weight, which, according to Mr.. Pc
risse, must be much higher for pinned
than for riveted bridges but it is none
the less true that Americans know how
to build fast and well.
Mr.. Regnard remarked that people
often made mistakes in talking about
the pins of American bridges. They
are not, properly speaking, bolts for
tightening joints, but, more accurate
ly, large joint pins of great diameter,
turned and fitted to within two ten
thousandths inch to the holes in the
parts which are to be united. AS to
the question of price, Mr.. Regnard
thinks that the American system ought
to be very cheap on accoun of its
lightness, and also because it is com
posed of parts which require little or
no forge work.