Washington sentinel. [volume] (Washington [D.C.]) 1853-1855, 1853-12-04
Railway Bridge at Niagara.

| Railway Bridge at Niagara.
This great work, which is to unite the Uni
ted States with Canada by railway, is rapidly
advancing, under the supervision of Mr.. John
| A. Roebling an engineer fayorably known in
connection with the suspension aqueduct on
| the Pennsylvania canal, at Pittsburg, and a
suspension bridge over the Monongahela, near
the same place. AS it is to be on some ac-
counts one Of the most remarkable mechanical
| achievements in the world we shall be par
| doned for devoting considerable space to a
| careful description of its plan and purpose. 1t
is well known that Stephenson, the Magnus
Apollo in engineering, whose fame rests upon
his tubular bridge over Menai Straits, has de-
cided against the suspension principle as ap-
piled to railway bridges, mainly on the ground
that it is incapable of rendering them suffi-
ciently stiff. The successful construction of
this work, therefore, at Niagara, will make an
| era in bridge building. 1t will be doing what
| has not merely never been done before, but
what has been pronounced by the highest au-
thority impracticable.
The present suspension bridge having been
constructed in l847, to aid in the erection of q
| railway bridge, will be removed after perform
| ing that service. Itwas begun by q boy on the
| Canada shore, who elevated q kite, and by that
| means established thread communication
with the other side. Over this tow.path wire
cables were soon formed.
The railway bridge will consist of two parts,
each suspended from two cables; a covered one
| for common travel, and above that on its roof
an open track for the railroad. 1t was first in
tended to build bridge with a single floor, but
the difficulty of rendering it wide enough for
purposes of horse, foot, and steam locomotion
| at the same time without making it too heavy
| nd too tba IL % h, ho,.
1 doned. The double floor of this brid dge simpi-
| fes the problem of rendering stiff support to
the weight of a railroad train, by placing under
it, in addition to other props, the trusses that
| will form the sides of the lower portion of the
bridge. The hollow tube, also, which that part
| will form, is expected to aid materially in
strengthening the work, operating like the tube
in Stephensons bridges.
The bridge will be 800 feet long, hung by
wire ropes, five feet apart, to four huge wire
cables, stretching from shore to shore, with a
considerable DETECTION, over the tops of towers
60 feet high. The towers are now far advanced
towards completion, having been begun some
four or five months since. They are Is feet
square at the base and 8 feet square at the top,
built of dark colored limestone, very hard
and compact. But the first operation, which
was commenced last winter, was to sink eight
shafts, 25 feet deep, in the rock below the tow
ers, four on each side of the river. In the bot
tom of each of these, enlarged for the purpose,
a cast iron plate, six feet square, was placed,
to which an immense chain was fastened. The
shaft was then filled in with masonry, the chain
being imbedded in a mixture of cement, lime,
and sand These chains reach the surface,
outside the base of the towers, and are to con-
meet with he cables. They will be &C feet long,
each consisting of eight links. They average
over eight feet iu length. The links are made
alternately of seven and eight plates of wrought
iron, each plate formed into one piece without
a weld. Each link Of eight plates has sand
wiched in, to use an expressive phrase, the
plates of the sevenfold link, and the whole fif
teen are riveted firmly together by an iron bolt,
- inches in diameter. The anchor-plate at
the bottom Of the shaft cannot be lifted until
the whole rock is raised bodily, with all its in
cumbent masonry. Nor can the plates and
chains give way from any force which can be
withstood by the cables, and they are calculated
to Withstand pressure four times greater than
the whole weight of the superstracture, com
bined with any load that will ever be placed
upon it. The towers, it will be observed, act
as fulcrums, between the chains on the one
side and the cables on the other, and the weight
of a loaded bridge will not act upon them side
ways but vertically.
The cables are to be GA inches in diameter,
| each formed of $500 strands of wire. Long
lines of wire are first formed, by fitting the
ends OF separate pieces to one another and
wrapping them round with smaller wire These
are then dipped in boiling oil and dried and
! the process is repeated a number Of times,
until coating is formed that will protect the
metal thoroughly from the moisture. The wire
is then wound round large cylinders. These
operations are now going on upon the Canada
shore. When the cable comes to be formed,
the wire will be drawn over to the American
side, one strand at a time, passed through the
link of a chain, then drawn back to the other
side, passed through chain there, and so on,
back and forth, until the whole cable is made
up; this will then be tightly wound round with
a small wire. The cables will connect with the
chains, after passing through iron saddles on
the top of the towers, there being iron clocks
with groove fitted TO the cable. Each saddle
rests upon a wrought iron roller, three inches
in diameter, that rolls on a smooth iron plate.
/ This is to accommodate any slight motion that
may arise from unequal tension between the
chains and cables when the balance is from
any cause disturbed.
Stephenson's great objection to the suspen-
sion principle, as we stated above, was the
| want of stiffness. 1t is conceded by the en-
gineer of this bridge, in his report on the sub.
ject that wire cables alone will not be sufficient
But he relies for stiffness, first, on the timber
placed under the railway. Two girders, as they
are called, or longitudinal timber, four feet
deep, are TO be placed in the upper floor, for
the immediate support of the track. In addi-
ton to these, are the trusses or sides Of the
lower bridge, which will consist of upright
posts, five feet apart, supporting the upper
floor, and connected with one another by a
light bridge and by iron rods. Any pressure
upon either floor is thus shared with the other.
| These rods are to be one inch in diameter and
| twenty-seven and one-third feet long, and will
connect the posts by 6ves, crossing at right
angles, between the top and bottom Of the first