Stone bridges appear to have originated among the Romans, who were the first to employ the arch on an extended scale.
One with six arches, commenced by Augustus and finished by
Tiberius, as its inscription indicates, still exists at Rimini.
Others, some of which are yet in service, constructed by that remarkable people, are found, touched to a greater or less degree by the hand of time, in different parts of the former
Roman Empire.
Their stability, no doubt, was in great part due to the massive character of their foundations, as the builders, not employing the coffer-dam, used immense quantities of stone.
(See coffer-dam.) Trajan (A. D. 105) built a magnificent bridge across the
Danube at Gladova; it was 4,770 feet long, and consisted of 22 wooden arches, resting on 23 stone piers.
It was destroyed by Hadrian, to prevent the incursions of the Dacians.
See
b,
Fig. 924.
The first stone bridge in
England was Bow Bridge, built in 1118.
The bridges of the
Middle Ages also possess great durability, as those remaining attest.
Their piers were founded on piles, the spaces between which were filled in with stone, necessitating, after a time, the driving of other piles outside these, until the substructure frequently, as in the case of Old London Bridge, seriously obstructed the water-way and impeded navigation.
This was built by Peter of Colechurch, 1176-1200, with houses on each side, connected by arches of timber, which crossed the roadway.
This was burned in July, 1212, and 3,000 persons perished.
It was restored in 1300; again partially burned in 1471, 1632, and 1725.
The houses were pulled down in 1756, and finally the bridge itself, to make way for New London Bridge, constructed by the Rennies, opened in 1831.
On this occasion the original piles, mostly of elm, were found to be but partially decayed, some portions being even used for making articles of utility or curiosity.
The new bridge cost £ 506,000. The daily travel in 1859 was about 20,498 vehicles, carrying 60,836 persons, and 107,074 foot-passengers.
This is the spot from which
Macaulay's “New-Zealander” is supposed to view the ruins of the old city once known as
London.
At a later, though comparatively recent period, the plan of sinking caissons (a kind of wooden case filled with stone) to form pier foundations, was introduced.
The coffer-dam succeeded these, to be itself succeeded by the pneumatic caisson, a vast improvement on the unwieldy structure formerly used.
See caisson.
In the construction of a stone bridge, when the coffer-dam or the pneumatic caisson is used, the river-bed is excavated until firm, hard bottom is reached, the abutments and piers of masonry are built up to the springing points of the arches, which are then turned upon the wooden centerings, which at once serve as a former for the arch and a support for its weight until the keystone course is laid.
They thus perform a function of great importance, and great care and skill are required in their construction.
When the masonry is complete, the centerings are removed, and the amount of subsidence, when this is done, affords a test of the skill of the architect and the faithfulness of the workmanship.
If the piers have been solidly built on a firm foundation, and the arch-work accurately and strongly laid, there should be little or no subsidence.
The bridge of Neuilly, by
Perronet, settled two feet; Waterloo Bridge but five inches. The spandrels are afterward built up, the spaces between the arches filled in, the roadway and parapet completed.
See arch; centering; bridge.
The following table embodies some facts in relation to a number of the most remarkable stone bridges in the world.
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Diagram of European bridges, showing the forms and proportions of arches. |
1. Vielle Brionde, over the Allier.
2. Holy Trinity, over the Arno.
3. Pont-y-Prydd.
over the Taaf.
4. Mantes, over the Seine.
5. Blackfriars, over the
Thames.
6. St Mascence, over the Oise.
7.
Waterloo, over the
Thames.
8.
Gloucester, over the
Severn.
9.
London, over the
Thames.
10.
Chester, over the
Dee.
11. Great Western Railway, over the
Thames at Maidenhead.
A remarkable bridge (3) was built in 1751 across the Taaf,
in Glamorganshire, Wales, by
William Edwards, a country mason.
He had previously erected two bridges on the same spot: the first was carried away by a sudden and extraordinary flood;
[
2394]
the second by the crowding up of the crown of the arch by overloading its haunches before the parapet was finished.
Peronnet could have taught him better, but
Edwards was a skillful and persevering man, and ultimately succeeded.
The present bridge has a span of 140 feet, rise of 35 feet, and is a segment of a circle 175 feet in diameter.
To avoid the subsidence of the haunches,
Edwards made cylindrical openings through them, 3 in each haunch, the lower opening being 9 feet in diameter, the next 6, and the upper one 3 feet. The bridge is widest at its abutments by the amount of 1 foot 9 inches. The width of the bridge at the crown is 11 feet.
The longest bridge in
England is that built by
Bernard Abbot of
Burton, over the
Trent at
Burton, in the twelfth century.
It is all of squared freestone, is strong and lofty, is 1,545 feet in length, and consists of 34 arches
Most of the 339 bridges of
Venice are of stone.
The “Union arch” of the
Washington Aqueduct over
Cabin John Creek has 220 feet span, is 450 feet long, 20 feet 4 inches wide; the elevation of the roadway above the bed of the stream is 100 feet. Cost to May, 1872, $237,000.
