The Republican. [volume] (Oakland, Md.) 1877-current, 1877-12-01
A Railroad Structure Almost Two
Miles In Length.

THE longest railroad bridge in the
world was opened for public travel near
Dundee, Scotland, recently. The struct-
ure thus opened spans the estuary of the
Tay at point almost two miles in width.
1t has been constructed for the purpose
of affording facilities for the more con-
venient conduct of the traffic of the
North British Railway Company. Hith-
erto the North British Railway Company
had to carry their traffic across the Tay
by means of ferry, and this method
was not only expensive, but exceedingly
slow. Accordingly, their engineer, Mr..
Bout, prepared the plans of the bridge
which has now been completed. Parlia-
mentary sanction was obtained in 1870,
the bridge being constructed as a sepa-
rate undertaking, with a capital of ST.
100000.
The contract for the work was OBJ
tanned in May, 1871, and the foundation
stone was laid in the land abutment on
the south side on the 22d of July of the
same year. The bridge begins about a
mile and a half above Newport, on the
south side of the river, where the depth
of water at high spring tides is forty-tive
feet, the velocity of the current reach
ing occasionally five knots an hour. To
bridge this formidable stretch of water,
the engineer planned bridge of eighty
five feet spans, varying in length from 81
feet to 245-those of the largest size, to
the number of thirteen, being placed over
the navigable part of the river. In this
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to provide for the passage of such ship
ping as frequents the ports of Newburg
and Perth, the bridge has a clear height
lightweight feet above high water, from
which it slopes down to the Fife side
with gradient of in $50, and toward
the Dundee side, where it takes a curve
to the eastward in order the more con-
veniently to join the land line
with a radient of 1 in 70. Cylin-
ders of iron and brick work with diam
eter of nine and one half feet, built on
shore in such lengths as would reach
from the rock on which they were in
tended to rest to point above low
water level, each consisting of cast
iron shell with lining of brick-work set
in Portland cement, leaving the inside a
central shaft three and one half feet in
diameter, through which the workmen
might pass up and down, were connected
by means of wall of brick-work about
five feet wide, thus placing a space of
twelve feet between their centres. The
whole being then made fast to a system
of strong iron girders, barges were in
troduced at low water underneath the
girdens, so that, when the tide rose, the
ponderous mass, weighing it might be as
much as 100 tons, was lifted bodily, and
quietly fioated out into the river. Hav-
ing been towed out to the site of the in
tended pier the cylinders were lowered by
hydraulic apparatus till they rested on
the river bottom. Workmen then de-
scended the internal shafts, excavated
the material from beneath the cylinders,
and so caused them gradually to sink
until they reached the rock in which a
level bed was cut for their permanent
resting place; but after the work had
been in progress for some time it was
found that the rock suddenly shelved
away to great depth under beds of
clay, gravel, and sand. 1t therefore
became impractible to sink the piers to
that foundation, and new method had
to be introduced. The weight of the
pier was lightened by substituting in the
upper works iron columns for solid brick,
while the adoption for each pier of a
single oval cylinder measuring twenty
three and one half feet by thirteen and
one half feet secured larger bearing
than had previously been obtained with
two smaller ones. The outer casing was
of malleable instead of cast-iron. When
the large masses were prepared they
were floated out and lowered to the river
bottom, the sand at the base being re-
moved by pump invented by one of
the assistant engineers. By the working
of the pump large cavity was speedily
formed under the cylinder, and the huge
mass of metal sank into it by its own
weight, reaching to a depth of about
eighteen feet below the bed of the river.
The interior of the cylinder was after
ward filled to the top with concrete,
and the upper part, so far as it stood
above the bottom of the river, was next
removed, thus leaving an ample plat.
form of artificial rock for the reception
of the superstructure, which consisted in
the first instance of brick-work in the
form of an elongated hexagon measuring
twenty feet by ten feet, and placed with
its greater length in the direction of the
current. This part of the pier was like
wise put together on shore and floated
out between barges in length of about
twenty feet, being sufficient, when placed
upon the cylinder, to reach above low.
water mark. From the low-water level the
! pier was formed of solid brick-work,
built in the ordinary way by workmen
brought alongside as the state of the tide
would permit; and at highwater mark
four courses of stone of an aggregate
thickness of four or five feet finished of
this portion of the work The piers of
fourteen spans were founded in this way,
the upper works being formed of iron
columns of twelve and fifteen inches
diameter.
When the piers had been brought to
! the necessary height, the girders, meas
uring 245 feet in length and weighing
100 tons for each span, were towed out
and deposited. The raising of the grid
ers when the piers had been completed
was carried in lifts Of twenty feet at a
time by hydraulic apparatus. Two grid.
ers, connected by transverse braces, go to
each span, the depths varying according
| to the width of the space to be crossed