Delaware state journal. [volume] (Wilmington, Del.) 1870-1883, 1883-08-16
BRIDaING THE F0R1H.


mel.
Boston Advertiser.
A new bridge, whose structure seems
almost wonderful, is to be thrown ACROSS
the River Forth, five mills west of F'' '
burgh, Scotland. This has been in coa-
temptation for years, but the width and
depth of The channel have until lately
proved too much for the engineers. Its
necessity is apparent. All the railroads
on the east side of Scotland from the
south find a terminus at Edinburgh. But,
in order to make connection with the
roads to Perth, Dundee, Inverness and
Aberdeen, it has been necessary either to
go due west rs miles to Stirling, where
the Forth is bridged, or to have a five
miles ferry transfer across the river lust
above Edinburgh.
The latter has been preferred in spite
of the occasional danger and inevitable
Inconvenience OF terriage across road.
stead of that width omen to the easterly
winds. In these days of rapid transit
this is no longer endurable. The plan
adopted by the engineers, Messrs. Fowler
and Baker, is striking example that
necessity is the mother of invention"
The bridge will be stretched between
north and Soulh Quesnferry, six miles
above Edinburgh. AT this point the
r-ver is miles broad, and half mile
from the north shore is the small island
of chsarvield. This would make
comparative easy problem were it not
that the depth of the water precludes
any piers for more than half the
distance. On the north the channel
Is 2l0 teet deep, and on the
south at least $50 feet. 1t is out of the
question to try to sink caissons 30 fer.
Sir Thomas Birch, who built the ILL
starred Tay bridge, proposed q suspen-
sion. This would have required for the
cables two stone towers on the islend
each $50 feet in hight, and on either bank
of the river one $50 feet high. They can
be better appreciated when it is said that
the towers of the Brooklyn bridge rise
but 27l feet above the East river. This
idea was speedily given up, and the
present one adopted. II shOuld be said
that as yet it is only a plan. Several
hundred men are at work preparing the
approaches, but the bridge is not con-
atructed. The plans, however, have been
approved by the best English engineers,
ana there Is no reason to apprehend
failure.
The principle is a very simple one.
An ordinary pier structure runs out q
little way on either bank. On the edge
OF the deep channel, near both banks.
four stone piers are placed in group.
and similar cluster will stand on the
south side of the island. Upon these
three supports will rest the entire weight
OF the bridge. Upon each one will b.
poised an immense cap OF steel, made in
the form of an elongated lozenge, with
the long axis representing the line of
railroad. The middle one will rest on
the tour island piers, which afford base
40 fest long, and will stretch out on
either side SIS feet. The two from the
shore piers will come within $50 feet of
meeting the centre one, aud to fill
the gaps, and resting upon the cages
TWO steel lattice girder brid.es will
be hung. The middle cage will
exactly balance upon its support
but the other two will have to reach ont
further over the channel than toward
land, and the balance will be made mn
by weights. In order to give NECESSARY
stiffness to such aspan from asinele base.
the structure has to be stitfened In every
manner. The plan of the elongated
lozenges gives each one hight above it,
pier OF $50 feet, sloping up from the pier
and down from the top to the connecting
lattice bridges. These lozsnge sbanad
affairs are really steel cages, 100 feet
wide at the bottom and only 30 feet at
the top This inward slope gives the
strength OF a trestle support, for all the
weight falls upon the piers
by uprishts, and not by The
arch principle from the side
The upper sides of the lozenees will ba
straight and the lower ones curved
while the tracks will run along their
horizontal axes l65 feet above the ton of
the piers, which will also be the altitude
OF the two connecting steel Orders. This
balance, or cantilever principle, has
never been used on large bridges before.
and Its introduction here will make one |
which will eclipse, as an engineering
wonder, the famous Brittanis and Vic |
toria tubular bridges. Some idea OF the |
magnitude of the work can be gained by |
knowing that il will take IS, 0O0. 600 and |
several years time.
AZ present the piers on the south side
are being put in, a gigantic undertaking
IN itself. On the north side thew arr
nearly completed. The bridge will be Of
Steel II every part except the piers. Ii
WIN thus be more costly, but lighter and
more durable. When done it will work
q revolution in the manner of buildins
long spans across deep channels.