Improvements in the Construction of Metal Bridges.
Year: 1896

page_text: Date of Application, 12th Nov., 1896
t
I, WALTER BEER, of 41 Corporation Street, Manchester, in the County of
Lancaster, Civil Engineer, do hereby declare the nature of this Invention to be as
follows:-
My invention relates to the construction of metal bridges and other similar
structures.
Hitherto the central portion of all bridges belonging to the cantaliver and central
girder type has been spanned by some form of girder, that is, by a structure having
practically only vertical reactions. Such structures impose very severe loads upon
the supporting cantalivers and necessitate their being either prolonged beyond the
piers or abutments to act as counterbalances, or otherwise anchored.
The object of my Invention is to reduce the severity of this loading and at the
same time to dispense with or materially reduce the counter balances above
mentioned, and this I effect by substituting for the central girder which spans the
space between the projecting cantalivers any suitable form of arch or arched
structure whereby I obtain oblique reactions instead of the ordinary vertical
reactions.
The arch is of metal of any suitable section and the central portion of the
platform or floor of the bridge is supported by the arch which abuts against the
cantalivers. In some cases it may be advantageous to reverse the arch and then
wire ropes might be employed.
In certain cases it may be expedient to absorb a portion of the horizontal reaction
from the arch by some addition to that structure and so long as the residual nortion
of this horizontal thrust or reaction is sufficient to cause a marked obliquity in the
resultant reaction it is advantageous as compared with a simple girder.
Dated this 11th dore of Narambar 1806
H. B. BARLOW & GILLETT,
Agents for Applicant.
COMPLETE SPECIFICATION.
Improvements in the Construction of Metal Bridges.
I, WALTER BEER, of 47 Victoria Street, Westminster, London, S.W., in the
County of Middlesex, Civil Engineer, (late of 41 Corporation Street, Manchester,
in the County of Lancaster,) do hereby declare the nature of this invention and in
what manner the same is to be performed to be particularly described and ascer-
tained in and by the following statement and accompanying drawings.
My said invention relates to improvements in the construction of metal bridges
of the well known cantaliver and central girder type.
Hitherto the central portion of such bridges has been spanned by some form of
n

page_text: girder or structure having practically only vertical reactions. Such structures
impose very severe loads upon the supporting cantalivers.
The object of my invention is to reduce the severity of this loading and this I
effect by substituting for the central girder which spans the space between the
projecting cantalivers any suitable form of arch, whereby I obtain oblique reactions
or thrusts instead of the ordinary vertical reactions.
The arch is of metal of any suitable section and the central portion of the
platform or floor of the bridge is supported by the arch which abuts against the
cantalivers.
In order that my invention may be clearly understood, I have annexed to this
Specification an illustrative sheet of diagrams.
Fig. 1 represents diagrammatically an ordinary cantaliver and central girder
bridge. A, A represents the cantalivers resting upon their piers or abutments B B.
C represents the ordinary girder which spans the gap between the two canta-
livers A A and is carried by them. It will be seen that the girder together with
its load bears vertically upon the projecting ends of the cantalivers and produces
vertical reactions R R as indicated by the arrows g g.
The tendency of the downward pressure from the girder C on the ends of the
cantalivers is to raise the other ends of each cantaliver in the direction of the arrows
marked a.
The severity of these reactions may be conveniently measured by their moments
about the points of support B B which mcments are represented by the algebraic
quantity Rx y.
My invention, as illustrated by Fig. 2, consists in substituting for the central
girder C hereinbefore described an arch D, abutting on the cantalivers thereby
obtaining oblique reactions R. R. The moments of these reactions about the
points of support B B may be measured by the formula R × 2
in the same way that the moments of the reactions from girder C Fig. 1 were
measured by the quantity R xy. By varying the rise or form of the arch D the
directions of R may be changed so that they will pass below the points of support
as in Fig. 2, through these points as in Fig. 3, or above them as in Fig. 4.
In the case of Fig. 2 Rxz may be made considerably less than Rxy in
Fig. 1. In Fig. 3, R x z will have no moment and in Fig. 4, Rx z will have
a negative value, (if Rxy in Fig. 1 be taken as positive) and will help to support
any loads upon the cantaliver arms e e or cause downward reactions at xx.
At the time of filing my Provisional Specification. I contemplated. the application
of my principle to structures other than bridges and I also proposed to reverse the
arch, but these, extensions of, my invention. I hereby disclaim.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is:
In metal cantaliver bridges, occupying the gap between the opposing ends of
adjacent cantalivers by an arch, so as to bring oblique thrusts to bear upon the
cantaliver instead of vertical reactions substantially as set forth.
Dated this 10th day of August 1897.
Dated this 10th day of August 1897.
For the Applicant,
E. K. DUTTON & Co.,
5 John Dalton Street, Manchester, Chartered Patent Agents.