The Sun.
London, England, 1863-01-28 00:00:00

The Great 71.stilway Bridge at Hungerford.

App ;rently in a few years more London will
show as many railways on its surf ;ce as it now has
lines of main sewers. They have long surrounded
it, they are now penetrating it, undermining it, or
stalking with iron strides across its crowded
streets; so that in the lapse of another ten
years or so it will come to pass that omnibuses
and cabs will be superseded like the post-chaise
and stage-coach of old, and in London at least
only used as feeders to the small but important
lines of railway which will reduce the limits of
this overgrown province of houses to as manage-
able dimensions in point of time as those of a
country town. Our distances are now too great,
cur time too precious, for mere horse power to be
of much avail. Straight short lines of rails, and
a pace of 25 miles an hour, are actual ne-
cesFaries in the transaction of London's daily busi-
ns, and as only railways can supply these wants,
reiiways are springing up to mat them on every
Two new railway bridges are already b-ing
Thames—one lofT the Char-

v bu

il)g-crosl Extension into Hungerford, one ;or the
Ch.tham and Dover in Farringdon-street ; arid a
third is about to be commenced by Mr. llawkshaw
between Southwark and London-bridges, to take a
line into Cannon-street near the Mansion-house, be-
tween which place and Charing-cross the train will
run backwards and forwards, like shuttles in a
loom, all day long. These bridges are more
or less remarkable for the skill shown in their
construction in designing them to be at once
the lightest, cheapest, and strongest struc-
tures of their kind, and in none are these
import ant qualities more prominent than in
Mr. Hawkshaw's bridge at Hungerford. Most
of our London readers have noticed the curious way
in which the massive iron work of this great erec-
tion has gradually enclosed the light and beautiful
proportions of Mr. Brunel's suspension bridge, and,
while enclosing it, seems also to have eaten its
way, plank by plank and iron by iron, till only the
brickwork towers and idle chains now remain to
show where the best proportioned bridge of this
kind in England once stood. In a month or so
more the chains themselves will be removed, and
the towers shorn down to mere stumps, when the
huge strength and massiveness of the new bridge
will be fully seen. Little more than this remains
to be done to complete this greatest of our railway
viaducts over the river Thames. This bridge has
so many purposes to answer, has so many diffi-
culties to overcome, and has so many contrivances
to eke out and opposite objects to fulfil, that it is
probably the most difficult work of the kind that
ever has been or will again be attempted across the
Thames. It is a railway bridge double the size in
width of any in the kingdom, a foot bridge twice as
large as old Hungerford; nearly one-third of the
bridge is a main station ; and, to crown all, though
the structure is of iron, the brick piers of the old
bridge had to be utilized in order to save cost. It
is, in short, a bridge of compromises and contriv-
ances, all met and all arranged with so much skill
that it discharges each duty as if built for that
alone, is very cheap, enormously strong, and withal
not nearly so ugly as railway bridges over rivers
generally are.

It is rather difficult in these engineering descrip-
tions to give the general reader a clear account of
such important works without using technical ex-
pressions, but in this case a mere outline of the
work itself and the nature of the duties it has to
perform will speak sufficiently for themselves. The
total length of the bridge from end to end is 1,360 ft.
its width between the main girders is 50ft., and
outside this there are two 7ft. footways for passen-
gers, making the total width 64ft. with a clear
headway above high water-mark of 25ft.
From the Surrey side to the brick pier of the old
structure on the Middlesex shore the bridge is carried
on a series of hollow east-iron cylinders or columns,
with a span of 154 ft. between each opening. But from
the Middlesex abutment, in order to make room at
once for a station with many sidings and starting
platforms, it widens out rapidly in a fan or trumpet
shape, and here the columns and general method of
construction have, as we shall see, to be entirely
changed. To begin, however, at the beginning, the
columns on which the bridge rests on its passage
across the river to the Middlesex abutment have a
diameter, at the base, of 14ft., while below the bed
of the river beneath which they go at depths varying
from no less than 30ft. to 38ft., and in all cases till
they have been sunk some feet into the London
clay. As these columns rise to near the surface of
the bed of the river they are diminished in thickness
by a sloping cast-iron joint, like a truncated cone,
which at its termination reduces the diameter of the
column to 10ft.—a size which it continues from low
water mark to the summit. These columns were
erected in the usual modern, simple way—that is,
placed on end at the precise spots they were in-
tended to occupy, and weighted till they were forced
beneath the bed of the river, when the water was
pumped out, and the mud and gravel removed down
to the level of the clay. Here they were again still
further forced down, the clay in turn removed, and
its place supplied with courses of solid masonry up
to the top of the 14ft. width. From this point
they were filled in with solid brickwork of the
hardest bricks that could be manufactured. Some
of the columns thus built have been steadily loaded
with railway iron to a weight of 750 tons, under
which enormous pressure, en so small a surface, the
masonry has been pressed together nearly two
inches, but beyond this no yield of any kind has
taken place, and each main pillar is now, as far as
experience and calculation can ascertain it, as firm
as if it was founded on a rock. Two such columns
fastened together at the top with a powerful wrought
iron close girder carry the road way in spans of 154 ft.
The main girders which bear all the strain of the
roadway in the long interval between each pair of
columns are the powerful lattices of wrought iron
which may now be seen on each side of the remains
of the old bridge. Tile visitor who inspects these
wonderful specimens of wrought iron work will find
that they consist, at top and bottom, of two
trough-shaped girders, 14ft. apart, the top one 4ft.
broad and the bottom 3ft., the uppermost one

being stronger as it has to resist the compressCy:
strain, which is always snore trying to wrought iron
than tension, which is met by the bottom girder of
3ft. broad. Though we have spoken of these as
two, and 14ft. apart, they are joined together and
made in reality one immense girder of that depth
by a latticework consisting of a series of struts and
ties, the struts to uphold against compression, the
ties to resist tension—in plain terms, to meet thrust
or pull in all parts of the structure. The struts
'vary from 12in. wide and 3in. thick to 6in. wide
and nin. thick. They are all placed in pairs,
and
may be known at once by their beliig
joined at the back with a r'erlal wrought
iron brApine, prevent their buckling out
under great pressure. The ties vary from 12in.
broad by 21-in. thick to 6in, broad by 2in. thick,
the greatest strength being given at the ends,
where the strain of the leverage comes. Each of
these pair of girders which carry the roadway be-
tween the columns is, as we have said, 154 ft long,
and the two are capable of bearing a lead strain of
1,500 tons, the greatest weight that could by any
possibility be put upon them if the four lines of
rails between them were loaded, with tank engines
and the footways outside thronged with people.
Even with such a load the strain would onlybe at
the rate of 4 tons per sectional inch at the top of
the girder, and 5 tons at the bottom—
a slight
weight when we remember that the Britannia
Bridge has a permanent strain of 7 tons to the
inch, and many wrought iron bridges both in
France and America have to do duty with
nearly twice that load. The floor of the road-
way between these main girders is foi med of
a series of cross girders placed as close as lift
apart. Each of these weighs nine tons, is
4f:t. deep, and equal to a load of 110 tons, though 77
tons is the greatest weight that could be placed
upon them. The two brick piers of the old bridge
are made to do duty in place of a pair of the circular
iron columns we have described, at some saving as
regards cost, but with a great loss as far as the uni-
formity of the structure is concerned. These brick
piers are to be cut down to the level of the old road-
way which so recenti.y hung to the chains, a hand-
some parapet and stone balustrade are to be erected