BRIDGES.
1811-1833.
Marykirk, Annan, Stirling, and Hutcheson stone bridges--High-level
bridge for Newcastle--Timber bridge of built planks--Winch
Chain Bridge--American bridges of suspension--Runcorn
Bridge--Menai Chain Bridge--New form of suspension bridge.
Mr. Stevenson’s stone bridges over the North Esk at Marykirk, and
the Nith at Annan (Plate VI.), are good specimens of road bridges
of moderate extent; and his bridge over the Forth at Stirling, and
Hutcheson Bridge over the Clyde at Glasgow (Plate VII.), are structures
of a larger class.
Of the latter, Mr. Fenwick, of the Royal Military Academy, Woolwich, in
the preface to his work on the _Mechanics of Construction_, published
in 1861, says,--“The London and Waterloo Bridges, in the metropolis,
which rank among the finest structures of the _elliptical arch_, and
Stevenson’s Hutcheson Bridge at Glasgow, which is one of the best
specimens of the _segmental arch_, together with many others, have
supplied me with a variety of problems for illustration.”
[Illustration:
_PLATE VI._
ANNAN BRIDGE
1824.
MARYKIRK BRIDGE
1811.
_W. & A. K. Johnston, Edinburgh._
]
[Illustration:
_PLATE VII._
HUTCHESON BRIDGE, GLASGOW.
1828.
STIRLING BRIDGE.
1829.
_W. & A. K. Johnston, Edinburgh._
]
[Illustration:
_PLATE VIII._
DESIGN FOR HIGH LEVEL ROAD BRIDGE AT NEWCASTLE ON TYNE.
1828.
TRANSVERSE SECTION.
_W. & A. K. Johnston, Edinburgh._
]
The Hutcheson Bridge was completed in 1832. The masonry of the piers
was laid at the level of seven feet below the bed of the Clyde, on a
platform of timber, on piles eighteen feet in length. I found by
a section made in 1845, after a lapse of thirteen years, that the level
of the river had been lowered, in consequence of the deepening of the
river Clyde by the Navigation Trustees, no less than eleven feet, and
even with that amount of scour the bridge was, and might long have
remained, a safe structure. But immediately above its site there is a
weir which dams up the Clyde and forms a lake, or almost still pool, in
the river’s bed for several miles. It was determined, in the interests
of navigation, to take powers to remove the weir, and on its removal
the bridge could, no longer be pronounced safe; it was also resolved to
take powers to replace the Hutcheson by the new Albert Bridge, designed
by Messrs. Bell and Miller.
* * * * *
Mr. Stevenson has also left behind him some traces of originality of
design in bridge-building.
In 1826 he gave a design to the Corporation of Newcastle for raising on
the existing bridge another roadway, on a high level, to communicate
with the higher parts of the town, as shown in Plate VIII., being the
idea since so successfully carried out on a large scale by the late
Mr. Robert Stephenson in his justly celebrated “high-level railway
viaduct.” Mr. Stevenson’s design, as will be seen, consists of piers of
masonry raised on the piers of the old bridge supporting a roadway of
cast iron. The upper bridge being continued across the quays on either
side of the river, and joining the roadways leading towards the south
and north by easy gradients, avoided the circuitous and dangerous route
of the old post road through Newcastle.
For timber bridges Mr. Stevenson also proposed, in 1831, a new form
of arch of a beautiful and simple construction (Fig. 16), in which
what may be called the “ring-courses” of the arch are formed of layers
of thin planks bent into the circular form and stiffened by _kingpost
pieces_, on which the level roadway rests. This form of bridge was
afterwards very generally employed for railway bridges before the
discovery had been made that for such works, structures of iron were,
in the end, more economical than timber.
[Illustration: FIG. 16.]
In 1820, he proposed to the Cramond District of Road Trustees, with a
view mainly to lessening the cost of the work, a form of suspension
bridge applicable to spans of moderate width, in which the roadway
passes _above_ the chains, and the necessity for tall piers is avoided.
The suspension bridge over the Rhone at Geneva, and other bridges, have
since been constructed on this principle.
In 1821 Mr. Stevenson wrote an article on Suspension Bridges for the
_Edinburgh Philosophical Journal_; and as it contains a description of
this new form of construction, as well as some historical information
relative to bridges on the suspension principle, a few extracts from
the paper may not be without interest:--
“_Winch Chain Bridge._--The earliest bridges of suspension of
which we have any account are those of China, said to be of great
extent; Major Rennell also describes a bridge of this kind over
the Sampoo in Hindostan, of about 600 feet in length. But the
first chain bridge in our own country is believed to have been
that of Winch Bridge over the river Tees, forming a communication
between the counties of Durham and York. This bridge is noticed
and an elevation of it given in the third volume of Hutchison’s
_Antiquities of Durham_, printed at Carlisle in 1794. As this
volume is extremely scarce, owing to the greater part of the
impression having been accidentally destroyed by fire, the writer
of this article applied for a sight of it from the library of his
friend, Mr. Isaac Cookson of Newcastle-upon-Tyne. The following
account is given by Hutchison at p. 279:--‘The environs of the
river (Tees) abound with the most picturesque and romantic scenes;
beautiful falls of water, rocks and grotesque caverns. About two
miles above Middleton, where the river falls in repeated cascades,
a bridge suspended on iron chains is stretched from rock to rock
over a chasm nearly sixty feet deep, for the passage of travellers,
but particularly of miners; the bridge is seventy feet in length,
and little more than two feet broad, with a hand-rail on one side,
and planked in such a manner that the traveller experiences all
the tremulous motion of the chain, and sees himself suspended over
a roaring gulf, on an agitated and restless gangway, to which few
strangers dare trust themselves.’ We regret that we have not been
able to learn the precise date of the erection of this bridge, but
from good authority we have ascertained that it was erected about
the year 1741.
“_American Bridges of Suspension._--It appears from a treatise
on Bridges by Mr. Thomas Pope, architect, of New York, published
in that city in the year 1811, that eight chain bridges have
been erected upon the catenarian principle, in different parts of
America. It here deserves our particular notice, however, in any
claim for priority of invention with our transatlantic friends,
that the chain bridge over the Tees was known in America, as
Pope quotes Hutchison’s vol. iii., and gives a description of
Winch Bridge. It further appears from this work that a patent was
granted by the American Government for the erection of bridges of
suspension in the year 1808. Our American author also describes
a bridge of this construction, which seems to have been erected
about the year 1809, over the river Merrimack in the State of
Massachusetts, consisting of a catenarian arch of 244 feet span.
The roadway of this bridge is suspended between two abutments or
towers of masonry, thirty seven feet in height, on which piers
of carpentry are erected which are thirty five feet in height.
Over these ten chains are suspended, each measuring 516 feet in
length, their ends being sunk into deep pits on both sides of the
river, where they are secured by large stones. The bridge over the
Merrimack has two carriage-ways, each of fifteen feet in breadth.
It is also described as having three chains which range along the
sides, and four in the middle, or between the two roadways. The
whole expense of this American work is estimated to have been
20,000 dollars.
“_Proposed Bridge at Runcorn._--Perhaps the most precarious and
difficult problem ever presented to the consideration of the
British engineer was the suggestion of some highly patriotic
gentlemen of Liverpool, for constructing a bridge over the estuary
of the Mersey at Runcorn Gap, about twenty miles from Liverpool.
The specifications for this work provided that the span of the
bridge should measure at least 1000 feet, and that its height above
the surface of the water should not be less than sixty feet, so as
to admit of the free navigation of this great commercial river. The
idea of a bridge at Runcorn, we believe, was first conceived about
the year 1813, when the demand for labour was extremely low, and a
vast number of the working classes of Lancashire were thrown out of
employment. A variety of designs for this bridge were procured by
a select committee of the gentlemen who took an interest in this
great undertaking. The plan most approved of, however, was the
design of a bridge of suspension; and Mr. Telford the engineer, and
Captain Brown of the Royal Navy, are understood pretty nearly to
have concurred in opinion as to the practicability of such a work.
Mr. Telford has reported fully on the subject, and has estimated
the expense of his design at from £63,000 to £85,000, according to
different modes of execution. Though as yet little advancement has
been made in carrying this enterprising design into execution, yet
the novelty and magnitude of an arch of 1000 feet span is a subject
of so much interest that we have thought it proper in this place to
mention these circumstances.
“_Menai Chain Bridge._--The Straits of Menai, which separate
the island of Anglesea from Caernarvonshire, have long formed a
troublesome obstruction upon the great road from London to Dublin
by Holyhead, by which the troublesome ferry of Bangor might be
avoided. Many plans for the execution of this undertaking have also
been agitated, chiefly in cast iron, including a range of estimate
from about £128,000 to £268,000; but that which is now acted upon
is a bridge of suspension upon the catenarian principle, the extent
of which between the piers or points of suspension is to be 560
feet, the estimate for which is only about £70,000. This by many
has been considered a work of great uncertainty; but the Union
Bridge on this plan has already been executed on the Tweed, to the
extent of 361 feet.”
Mr. Stevenson then goes on to mention several wire and chain bridges
erected in Scotland, and gives the following description of his design
for Cramond Bridge:--
[Illustration: FIG. 17.]
“Fig. 17 is a section and plan designed for crossing the river
Almond on the great north road between Edinburgh and Queensferry.
The extent of the span between the points of suspension is laid
down at 150 feet. The chief circumstances which particularise
this design are a mode of fixing the chains to the abutments of
suspension on each side of the river, by which the main chains
can be distributed equally under the roadway. The main chains are
likewise made to collapse or turn round the abutments of masonry,
as will be seen from the section, in which the parts of the work
are so contrived that access can be had to the chains by an arched
way on each side. In this design the two ends of the chains are
formed into great _nails_ or bolts, with countersunk or conical
heads made to fit into corresponding hollow tubes of cast iron
built into the masonry of the abutments.
“From this description the reader will readily form an idea of the
simplicity and effect of this mode of fixing the chains, being
such, also, that any particular chain may be withdrawn and replaced
without deranging the fabric of the bridge. The roadway, instead of
being _suspended_ from the main chains, is made up to the proper
level upon the chains by a framework of cast iron, prepared for the
reception of a stratum of broken stones for the road.
“The making up of the roadway of this bridge, however, and the
enlarged angle of its suspension, may be considered as limiting
the span or extent of bridges of this construction to about 200
feet. The structure represented by Fig. 17 appears to possess many
advantages for bridges of that modified extent, and the manner of
fixing the chains is applicable to all bridges of suspension; it is
likewise new, so far as we know.”
In the close of his paper Mr. Stevenson says:--
“To what extent suspension bridges may be carried is very
uncertain, and he who has the temerity to advance sceptical or
circumscribed views on this subject would do well to reflect upon
the history of the steam-engine. When the Marquis of Worcester
first proposed, by the boiling of water, to produce an effective
force, no one could have conceived the incalculable advantages
which have since followed its improvement by our illustrious
countryman, Watt.”
A prophetic announcement, which has had its full realisation in the
Suspension _Railway_ Bridge of 821 feet span at Niagara Falls, and in
the still bolder design now in execution for connecting New York and
Brooklyn by a steel wire suspension bridge, having a clear opening
between the piers of no less than 1600 feet.