IMPROVEMENTS IN SWING BRIDGES
Year: 1875

page_text: PROVISIONAL SPECIFICATION left by Alexander Meadows Rendel at
the Office of the Commissioners of Patents, with his Petition, on
the 25th February 1875.
I, ALEXANDER MEADOWS RENDEL, of 8, Great George Street, West-
minster, do hereby declare the nature of the said Invention for
"IMPROVEMENTS IN SWING BRIDGES," to be as follows:-
:-
Heretofore swing bridges for bridging across the entrances to and the
channels in docks and other such like channels have been commonly
mounted upon a pivot carried by the masonry on one side of the
channel, and the overhanging weight of the bridge upon one side of the
pivot has been counterbalanced by a continuation of the beams upon
the opposite side of the pivot and the addition of balance weights; this
necessitates the construction of beams of considerably greater length
and strength than the width of the entrance or channel to be bridged
over would in itself require, and not only is a great amount of space
thereby occupied, but also the cost of the structure is materially
increased.
•
By my Invention I am enabled to employ girders but little longer
than the channel to be crossed and to dispense with the balance weights

page_text: now employed; this I effect by placing under the bridge at any con-
venient point in the passage to be crossed an open framework or a water-
tight pontoon, as may be judged from the circumstances most con-
venient, carried downwards from the bridge and provided at the bottom
with rollers to run on a roller path formed as in the case of lock gates |
at the bottom of the passage and concentric with the pivot at one end
of the bridge upon which the bridge swings; in order also that the
bridge when in position across the entrance or channel may rest at its
two ends upon solid supports and yet be casily freed from these supports,
when it is required to turn the bridge to one side I place a hydraulic
cylinder or cylinders below the pivot or pivot end of the bridge by
which that end can be raised or lowered. When the bridge is across the
entrance and is to be turned to one side, the pivot end of the bridge is
thus raised and the blocks or supports upon which the bridge previously
rested at the pivot end are removed from below it; the pivot end of the
bridge is then lowered thereby, in the first place bringing the rollers of
the central framework or pontoon down on to the roller path; then as
the pivot end of the bridge is still allowed to descend, the bridge turns
on the rollers or roller path as a pivot and the opposite end of the
bridge rises from its supports; the bridge resting upon the rollers and
pivot or pivot end is then free to be turned upon its pivot, and is moved
round by means of chains in a similar manner to that employed for
turning lock gates and is received into a recess in the masonry.
When the bridge is to be again moved across the entrance or channel
it is turned round by the chains as before to bring it into position. Tho
pivot end of the bridge is then raised first until the opposite end of the
bridge is lowered on to its supports, and then further to allow the blocks
upon which the pivot end is to rest to be put into position. The pivot
end of the bridge is then lowered until it rests upon these blocks, and
the bridge will thus be left resting at its two ends upon solid supports
carried by the masonry at the opposite sides of the entrance or channel,
or it may rest upon these solid supports and also in addition upon the
roller path at the bottom of the entrance through the framework or
pontoon which rest upon the rollers.
The framework and rollers by which the bridge is carried and turns
on the bottom of the passage must be so placed that the portion of the
bridge between them and the pivot end of the bridge shall be heavier
than the other portion; but the same effect may be produced by counter-

page_text: weighting the pivot end or by applying hydraulic or other power to
depress it.
The pivot end may be steadied in turning by rollers attached to it,
moving on a roller path below it, or otherwise conveniently placed.
The pivot must be so placed that when the bridge is turned back to
allow ships to pass the bridge shall be wholly within the line of the
quay wall on the pivot side of the passage. The exact position of the
pivot will depend on the width of the bridge.
In place of the pivot end of the bridge being raised, as above described,
to allow of the taking away or replacing the blocks or supports upon
which this end of the bridge rests, when the bridge is in position for
traffic to pass over it, these blocks or supports might themselves be
raised or lowered as required by means of hydraulic cylinders.
In order to facilitate the repairing of the rollers at the bottom of the
pontoon or framework, the rollers may be made readily detachable as in
the case of lock gates from the pontoon or framework, so that they may
be taken up and examined or replaced.
The recess in the masonry into which the pontoon or framework is
received when the bridge is turned to one side might also be provided
with a dam at its entrance to form it if required into a dry dock, or the
framework or pontoon might be so arranged as to be readily floated
away by the help of barges for repair, the bridge being in the meanwhile
left across the channel for use as a carriage or railway bridge. The
roller path may be kept clean by scrapers placed in front of the rollers,
and it may be also scoured by jets of water under high pressure directed
on to it whenever required. An air-tight casing provided with air
locks may also be carried down from top to bottom of the pontoon or
framework to give ready access to the roller path. In place of employ-
ing water power, as above described, for working the bridge, steam, air,
or other power may be employed.