Year: 1885

page_text: I, GEORGE GARSON of 2 Craiginillar Villas, Newington, Edinburgh in the
County of Mid-lothian, Civil Engineer, do hereby declare the nature of this
invention to be as follows:-
This invention which relates to improvements in stiffened suspension bridges
for passenger and other light traffic has for its object to construct a bridge which
shall at all points fulfil stringent conditions of engineering efficiency whilst its
weight and cost shall be less than that of a bridge constructed on ordinary.
principles to sustain or carry the like load.
The bridge under this invention consists of two horizontal members extending
across the space to be spanned and at each side resting upon abutments.
From vertical piers supported on each abutment chains extend in the form of a
bow above the said horizontal members and also across the space to be bridged
the chain at each side and the horizontal member beneath it being tied together
by diagonal bracings in such a way that each structure constitutes a side frame for
the carriage of the traffic platform or roadway the bracing giving to each frame
rigidity against deformation and vibration in a vertical plane. In this way there
is imparted to the structure a stiffness approaching that of the ordinary girder
bridge whilst at the same time the disposition of the bracing ensures that both
the upper and lower members of each side frame are subjected to tensile stress,
the stresses on the diagonal bracings themselves being small and nearly equal
throughout owing to the fact that the stress which in ordinary girder suspension
bridges with horizontal booms comes upon the bracing is in this case largely taken
up by the curved upper chain. On the chain itself the stress is least at the centre
of the bridge increasing towards the piers at either side at which it reaches a
maximum and on the lower horizontal members, on the other hand, the stress is
least at the abutments increasing towards the centre of the bridge where it reaches
a maximum.
The bridge is hinged at the centre so that it can rise or fall as a whole with
variations of temperature without being strained.
The piers which are preferably box shaped are hinge jointed at the base to the
foundation and pin jointed at their upper ends to the chains before referred to and
to the straining or anchoring ropes. The stress on them being thus always axial
they are subjected to no bending moment and in effect act simply as struts and
the stress on the foundations is thereby converted into a stress entirely of the
nature of a vertical load.

page_text: I, GEORGE GARSON of 2 Craigmillar Villas Newington, Edinburgh, in the
County of: Mid-Lothian, Civil Engineer, do hereby declare the nature of this
invention and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement :-
This invention which relates to improvements in stiffened suspension bridges for
passenger and other light traffic has for its object to produce a bridge which shall
at all points fulfil stringent conditions of engineering efficiency whilst its weight
and cost shall be less than that of a bridge built on ordinary principles to carry or
sustain the like load.
The bridge as constructed in accordance with the invention consists of two
horizontal members extending across the space to be spanned and at each side
resting on abutments. From vertical piers, contiguous to but independent of and
separate from the ends of the horizontal members, chains extend in the form of a
bow above the said horizontal members and also partly across the space to be
bridged the chains and horizontal members being tied together by diagonal
bracings in such a way that each structure composed of a horizontal member and
two chains constitutes a side frame for the carriage of the traffic platform or
roadway the bracing giving to each frame rigidity against deformation and
vibration in a vertical plane. By this formation there is imparted to the structure
a stiffness approaching that of an ordinary girder bridge the disposition of the
bracing ensuring that both the upper and lower members of each side frame shall
be subjected to tensile stress whilst the stresses on the diagonal bracings themselves
shall be small and nearly equal throughout owing to the fact that the stress which
in ordinary girder suspension bridges with horizontal booms comes upon the
bracings is under this invention largely taken up by the curved upper chains.
On the chains themselves the stress is least at the centre of the bridge and
increases towards the piers at which it reaches a maximum whilst on the lower
horizontal members the stress is least at the abutments and increases to a
maximum at the centre of the bridge the said lower horizontal members being
there hinged to permit the bridge to rise and fall as a whole with variations of
temperature and without being strained.
The piers are hinged at the base and pin connected to the chains at their upper
ends. The stress on them being thus rendered always axial they are subjected to
no bending moment and in effect act simply as struts, and the stress on the
foundations is entirely of the nature of a vertical load.
And in order that my said invention may be properly understood I have
hereunto appended an explanatory sheet of drawings illustrative of the system,
mode or manner in or under which it is or may be used or carried out in practice.
Of the drawings figure 1 is a side elevation and figure 2 a part plan and part
horizontal section of one half of a bridge constructed in accordance with my said
invention. Figure 3 is an end elevation and the remaining figures are details of

page_text: the construction drawn to larger and varying scales and are hereinafter more
particularly and individually referred to.
The bridge as illustrated on the drawings is supposed to be of 200 feet span but
it will of course be understood that any dimensions hereinafter given on that basis
are and must be varied according to circumstances.
Referring first to the piers A, these at each end are two in number and consist
of columns with a clear space of say 10 feet between them. Figure 4 is an end
elevation, figure 5 a transverse section and figure 6'a horizontal section of one pier
on a larger scale and as more clearly seen by figure 6 each column is of a box
shaped section formed of plates and angle irons rivetted together. The columns
are braced with horizontal struts B, and diagonal ties C, from near their summits
to within 12 feet clear above the level of the roadway and at their bases they are
hinged to cast iron base plates D, by means of steel bolts or pins a, the base
plates D, being secured to masonry abutments E by anchor bolts b.
The side frames of the bridge each consist of upper curved members F composed
of forged flat links of steel one of which is illustrated in detail at figures 7 and 8,
and lower horizontal members G, composed of steel plates of channel section placed
back to back as seen in cross section at figures 9 and 15.
The upper curved members F and lower horizontal members G, of each side
frame are braced together with tee iron struts H, and flat iron ties I. The spaces
between the connections of the struts and ties to the members G are equal to one
another as are also the spaces between the connections to the members F but the
said spaces in the members F, are collectively one less in number than the spaces
in the lower members G, the spaces in the latter being say 10 feet apart whilst in
the former they are about say 10 ft 9 inches apart. As seen by figures 1 and 12
the upper member F is non-continuous over one space at the centre of the span
while the lower member G, is hinged at the centre of the said space the joint being
formed as seen at Figures 12, 13 and 14 by means of a steel bolt or pin c, passing
through steel plates d, rivetted to the non-continuous ends of the channel steels
forming the lower member.
Inasmuch as the two links F nearest the centre of the bridge in each half side
frame may be occasionally subjected to a compressive stress these links are as seen
more particularly at figures 12 and 13 constructed each of two flat bars of steel
kept apart by cast iron distance pieces d, spaced at intervals of about a foot
between the bars and through these pieces wrought iron or steel rivets e, pass :—
further at each end of the said links a stay L, formed of tee and plate iron is
employed one end of the said stay being secured by bolting to the end of the
link and the other by rivetting to the lower member of the side frame as indicated
at figures 1 and 12.
The ends of the lower members which rest on the abutments E, are as seen
more particularly by the details figures 9, 10, and 11 bolted down thereto by two
anchor bolts f, of iron working in slot holes g, to permit of the expansion and
contraction of the frame consequent on variations of temperature and the con-
nections between the piers A, and the upper members of the side frames are made
of steel bolts h, as are also all the counections between the different members of
the frame F.
Figure 5, illustrates in detail the connection of the links F and bracings H, I, to
the piers figs. 16 and 17 the connection of the links and bracings; and figures 18
and 19 the connection of the bracings with the lower members.
Between the lower members G, extend cross girders K, consisting of single bars
of channel steel spaced at about 3 feet 4 inches apart these being as seen at
figures 20 and 21 rivetted to the upper flanges of the lower members. Besides
these cross girders diagonal wind bracings consisting of round iron bars secured to
the lower members as seen at i, fig. 20, are employed the cross girders K, acting
as struts for the said bracings.
The decking M, of the bridge consists of teak or equivalent planking secured to
the cross girders K by iron fang bolts j, as seen at fig. 15, and the side rail is

page_text: preferably composed of round iron bars passing through and carried by uprights o,
of angle iron these uprights being secured to the ends of the cross girders by
rivetting.
The anchorages of the bridge which may be of any suitable construction and
have any well known straining apparatus adapted or applied thereto are connected
to links N, P, figures 1 and 5 which are also pin jointed to the piers as indicated.
From the construction of stiffened suspension bridge herein before described and
illustrated it will be observed that the disposition of the bracing H, I, ensures that
both the upper and lower members of each side frame are subjected to tensile
stress whilst the stresses on the bracings themselves are small and nearly equal
throughout the stresses which in ordinary girder bridges with horizontal booms
come upon the bracings being in this case largely taken up by the curved upper
chain. It will also be seen that the stress on the chains is least at the centie of
the bridge increasing to a maximum at the piers A, whilst on the lower horizontal
members the stress is least at the abutments and increases to a maximum at the
centre of the bridge where the plates constituting the said members are heaviest.
Fig. 22, illustrates the mode of splicing a heavier and a lighter plate in the length
of the horizontal members.
The piers being hinged at their base and pin connected to the chains at their
upper ends the stress on them is always axial and in effect they act simply as
struts being subjected to no bending moment.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that what
I claim is :-
1. In a suspension bridge, a side frame composed of vertical piers hinged at
their lower ends and of a continuous lower member and two non-continuous upper
Inembers, these continuous and non-continuous members being braced together by
struts and ties and the non-continuous members pin-jointed to the piers sub-
stantially as hereinbefore described with reference to the drawings annexed.
2. In a suspension bridge of the construction hereinbefore set forth staying the
two links F of the upper member nearest the centre of the bridge by stays L,
secured by bolts to the ends of the links and by rivets to the lower members G 88
and for the purpose described.
Deted this Eighth day of lune 1886