Burlington weekly free press. [volume] (Burlington, Vt.) 1866-1928, 1883-08-10
BRIDGING THE FORTH,
The Marvellous structure Which IL to
span the flushing scotch Chan.
From theI Boston Advertlser.l

|
From theI Boston AdvertiserJ
new bridge, whose structure seems al
most wonderful, is to beIthrown across the
| River Forth, five miles west of Edinburgh,
Scotland. This has been in contemplation
for years, but the width and depth of the
channel have until lately proved too much
or the engineers. Its necessity is apparent
All the railroads on the east side of Scotland
from the south find terminus at Edinburgh.
But, in order to make connection with the
roads to Perth, Dundee, Inverness and Aber-
den 1t has been necessary either to 60 due
west twenty-five miles to Stirling, where the
Forth is bridged, Or to have u five miles ferry
transfer across the river just above Edn-
burgh
The latter has been preferred in spite of
the occasional danger and inevitable incon.
venience OF ferriage across a roadstead of that
width open to easterly winds In these days
OF rapid transit this is no longer endur-
ablei The plan adopted by the engineers,
Mcssrs. Fowler and Baker, is striking
example that necessity is the mother of
invention" The bridge will be stretched
between North and South Quccnfcrry six
miles above Edinburgh. At this point the
river is one mile and one half broad, and half
mile from the North shore is the small
island of lnchgarvield. This would make
comparatively easy problem were it not that
the depth Of water precludes any piers for
more than halt the distance. On the north
the channel is 2l0 feet deep. and on the south
al least $50 feet. 1t is out of the question to
try to sink caissons SO far. Sir Thomas
Burch, who built the ill-starrcd Tay bridge,
Dr0nOspd "a gIlsnpnSinn W In
CURED for the cables two stone towers on the
island, each 500 feet in height and on either
bank of the river one 5S4 feet high, They
can be better appreciated when it is said that
the towers OF The Brooklyn bridge rise but
271 feet above the East river. This idea was
speedily given up and the present one adopt
ed. 1t should be said that as yet it is only
plan. Several hundred men are at work pre-
pairing the approaches, but the bridge is not
| constructed. The plans, however, have been
approved by the best English engineers, aud
| there is no reason to aprrehend failure.
The principle is a very simple one. An
ordinary pier structure runs out a little way
| on either bank. On the edge of the deep
| channel, near both banks, four stone plers 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 be
poised an immense cap of steel, made IN the
| form of an elongated lozengc, with the long
axis representing the line Of railroad. The
middle one will rest on the four island piers,
which afford base 270 feet long, and will
stretch out on either side 675 feet. The two
from the shore piers will come within $50
feet Of meeting the centre one, and to fill the
gaps, and resting upon the cages, two steel
lattice girder bridges will be hung. The
middle cage will exactly balance upon
its support, but the other two will have
To reach out farther over the channel
than toward land, and the balance will
be made up by weights. In order to give the
necessary stiffness to such span from
single base, the structure has to be stifened
in every manner The plan of the elongated
lozenges gives each one height above it's
pier of $50 feet, sloping up from the pier
and down from the top to the connecting
lattice bridges. These lozengc-shaped affairs
are really steel cages, 100 feet wide at the
bottom and only thirty feet at the top, This
inward slope gives the strength of a trestlo
support, for all the weight falls upon the
piers by uprights, and now by the arch prin-
clple from the side. THE upper sides of the
lozenges will be straight and the
lower ones curved, while the tracks
will ran along their horizontal axes
l65 feet above the top of the piers,
which will also be the altitude Of the two
connecting steel Orders This balance, or
cantlever principle, has never been used on
large bridges before, and It's introduction
here will make one which will eclipse, as an
engineering wonder, the famous Britannia
and Victoria tubular bridges Some idea Of
the work can be gained by knowing that it
will take IS, 900, 900 and several years time.
AT present the piers on the south side are
being put in, "a gigantic undertaking in itself.
On the north side they are nearly completed.
The bridge will be OF steel in every part ex-
cept the piers. 1t will titus be more costly,
, but lighter and more durable. When done
, it will work a revolution in the manner of
building long spans across deep-channels.