There are two other large brick bridges over the Thames, one at
Gathampton and another at Moulsford, that at Moulsford crossing the
river obliquely at an angle of 45°. In each of these bridges there are
four arches, of 62 feet span on the square.
Other good examples of brick bridges are the turnpike road bridge, 60
feet high, with three arches, across the deep cutting at Sonning Hill,
and the bridge, with one opening of 60 feet and four side arches of 18
feet span, over the river Kennet at Reading.
The bridge over the Avon at Bathford, of 87 feet span, and the bridge
crossing the same river at Bath, with an arch of 88 feet span, are
handsome Bath-stone structures with semi-elliptical arches. Near Bristol
there is an ornamental bridge of masonry with three Gothic arches, the
centre arch having a span of 100 feet.[83] Another bridge of Gothic
design, with two arches of 56 feet span, carries the railway over the
Floating Harbour.[84]
* * * * *
The bridges which have hitherto been noticed are all on the Great
Western Railway. On the Bristol and Exeter Railway there is a large
stone bridge over the New Cut at Bristol, built in 1840, which has a
single segmental arch of 120 feet span, and 20 feet rise. Owing to some
imperfect workmanship in the interior masonry of the arch, and possibly
to some unequal yielding of the abutments, the crown sunk much more than
had been expected.
On his later railways Mr. Brunel did not build large arches of brickwork
or masonry, though he constructed several lofty and extensive viaducts
of these materials with spans varying from 40 to 60 feet.
Mr. Brunel seldom employed artificially piled foundations to support
masonry. When the ground was soft, he preferred to rely on a large
extent of bearing surface, and ensured uniformity of settlement by an
accurate distribution of the load. Several of his large viaducts and
bridges, standing on ground of a soft and spongy nature, were
constructed on this principle.
A class of bridge of striking outline was used in the cuttings on the
Bristol and Exeter Railway, and on the other railways subsequently made.
Bridges of this class were called flying bridges. Instead of arches
resting on piers and abutments, the bridge has a single arch, reaching
from one side of the cutting to the other, and springing from the
slopes, which it helps in some measure to support. A flying bridge of
large dimensions near Weston-super-Mare carries a road across the
cutting at a height of 60 feet above the line of rails, with a clear
span of 110 feet.
The quantity of masonry in these bridges is much less than in those of
the ordinary construction; and lofty and expensive centering is not
required, as the bridge can be built before the cutting is excavated to
its full dimensions.
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