Improvements in Suspension Bridges.
Year: 1891

page_text: Date of Application, 5th Aug., 1891-Accepted, 17th Oct., 1891
COMPLETE SPECIFICATION.
Improvements in Suspension Bridges.
I, LOUIS CORMEROIS, of Nimes (Gard) France, 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 :-
Suspension bridges consist usually of flexible cables secured at each end to
towers and supporting the roadway by means of suspension rods or cables. Such
cables have in consequence of their shape, the great drawback of undergoing
considerable deformation under the action of rolling loads and of gusts of wind.
This invention has for object to construct suspension bridges and similar
structures in such a manner that these disadvantages are obviated, as I will now
proceed to explain by aid of the accompanying drawings in which :-
Figs. 1, 2, and 3 are diagrams.
Figs. 4, 5, and 6 are diagrammatic views of bridges constructed according to this
invention.
Figs. 7 and 8 are diagrammatic views drawn to a larger scale, of parts of a
bridge.
Figs. 9, 10, and 11 are diagrammatic views illustrating modified constructions of
bridges.
Figs. 12, 13, 14, 15, are views illustrating details of construction.
Fig. 16, is another diagrammatic view of a bridge.
Figs. 17, 18, and 19 are views illustrating other details of construction.
My invention is based on the following principles :-
1. Let a, b, a, b, (Fig. 1.) be four fixed points arranged in the same vertical
plane and connected by means of well stretched cables. At the point of inter-
section o let there be a strong ligature or connection so that the two cables shall
not be capable of sliding one past the other under the action of any force. The
point o will then be rigidly fixed; it is not capable of shifting in either of the four
directions indicated by the arrows, and if we consider its movement in any direction
as being possible, from the bottom upwards for example, such movement can only
take place to the extent to which the parts of the cables a o and bo shall become
elongated. The same holds good for movement in the other directions.
2. Let d, d (Fig. 2) be two points located on the diagonal cables and in the
same vertical plane; let them be connected by a rigid bar. At any point c of this
bar let there be applied a weight. The part c, d, of the rigid bar will be in
tension and the part c d will be in compression, and the points d and d will have a
tendency to move downwards. As regards the point d, this downward movement
can only take place to the extent permitted by the movement of the point o, or
from right to left, or from below upward. Now it will be seen from Fig. 1 that
such movement is impossible, since in the first case it would entail the lengthening
of the cables bo and bio, and in the second case the lengthening of the cables a o, o. b,
and similarly the raising of the point d which is subjected to an opposite action by
the weight. Thus every point taken on the right bar d d¹ is fixed.
3. If on the same diagonal cables (Fig. 3) four points e, e', f, f', be taken, located
two by two in the same vertical plane, and the points f, el, and e, f, be connected
together by cables, and a strong connection be made at their point of intersection c'
this point c will also be a fixed point, for the reasons just given.
I have applied the preceding principles to the construction of suspension bridges
as I will now explain.
A. A¹ (Fig. 4) are the abutments of a suspension bridge; B B' are the abutment
towers. From the summits a, b, of these abutment towers are stretched two
diagonal or oblique cables a¹ b; 'a which are anchored to the abutments at the

page_text: points a and b, and are firmly connected together at the point of intersection o;
this point o, which is situated on the vertical axis of the span, will be a
fixed point. By attaching the road-way to this point by means of a suspension
rod o o', there is obtained at o' a fixed support which is equivalent to a pier. From
the fixed point o there may extend diagonal stays, hereinafter called stiffening stays,
which play the same part in the support of the road-way as the cables extending
from the summits of the abutment towers.
If on the other hand, as stated above, two points d, d¹, located on the cables and in
the same vertical line, be connected by a rigid bar, any point c of this bar will
be a fixed point and, as in the case of the point o, a suspension link and diagonal
stays can be attached thereto. Finally, analogous points c¹ can be obtained by
connecting together, as shown, four points e, e, f, f, on the main cables by other
cables e, and ef, and by firmly connecting these latter at their point of inter-
section c. Thus it will be seen that the arrangement allows of obtaining as many
fixed points as may be desired.
Fig. 5 illustrates the application of my system of construction to a bridge having
several spans, each say 100 metres long.
A is the abutment on the shore; P is one of the piers, B B' are the abutment
towers surmounting the abutment and the pier respectively. a' b, a b', are the
oblique cables which pass over the summit of the abutment towers and are anchored
at the points a and b to the abutment and to the pier respectively. The road-way
is divided into equal parts each of 5 metres length. There are thus 20 divisions in
each span. From the summits of the abutment towers are led the diagonal or
stiffening stays a'-1, a'-2, a¹-3, a¹-4,
, 6¹-19,
6-18, -17, 61-16
up to the limit of inclination of three at base
to two in height.
...
At the point of intersection o of the oblique cables are fixed a suspension
rod o 10 and the stiffening stays o-8, 0-9, o--11, 0-12.
At the divisions 6 and 14 are arranged the rigid bars d d', dd, and at the
centres c and c' of these bars are fixed, as in the case of the point o, the suspension
rods c-6, c-14, and the stiffening stays c-4, c—5, c—7, c—8,
c'-12,
c-13, c-15, c¹-16.
Such is in general arrangement the construction of one of the spans according to
my invention for bridges of ordinary length. The road-way is supported at points
5 metres apart, and this enables it to be considered as a series of small girders of
5 metres in length. The intermediate points of support c, o, c¹are fixed points.
The two longitudinal girders extending the whole length of the span, are supported
by rods and stays led from these points, and are every where of the section of
an edge or side girder of a bridge of 5 metres span without cross beam; these
longitudinal girders may therefore be considered as a series of girders of 5 metres
length resting freely on 2 supports. Transverse girders arranged as hereinafter
described, complete the metallic skeleton of the structure.
Fig. 6 illustrates the application of my system of construction to a bridge of a
single span of 500 metres.
Fig. 7 illustrates, to a larger scale, that portion of the bridge which is adjacent
to the abutments.
Fig. 8 illustrates, also to a larger scale, the central portion of the bridge.
A. A are the abutments; B, B', are the abutment towers which may be say
37 metres in height. The points of anchorage a and b are taken at distances of
17 metres below the roadway.
With the object of having suspension rods and stiffening stays not longer than
10 metres length for the former, and 17 to 18 metres length for the latter, these
points a and b should always be at a distance (for large structures and whatever
may be the length of the spans) below the road-way such that the difference
between the height of the abutment towers and this distance shall never be greater
than 20 metres. I have fixed it at this amount for all structures. Thus for a
span of 500 metres, the abutment towers being 37 metres high, the points of

page_text: anchorage a and bare 37 metres less 2017. For a span of 1000m length, and abut-
ment towers of 60m height, the same points a and b would be 60 - 20 = 40" below
the road-way. The intermediate points of support c, c, c², etc., are thus situated at
a uniform height of 10m above the road-way. This is of importance especially
from the point of view of rigidity of the road-way, and of economy in the cost of
construction.
The road-way for the bridge (Figs. 6, 7 and 8) is divided into equal portions
each of 5 metres length, thus making 100 divisions; the stiffening stays are led
from the abutment towers, and the cables a¹ b, a b' are arranged in place. Ou the
horizontal line starting from the point of intersection o of the cables there are taken
at every 30%, the points c, c, c³, c², c¹,
c¹, c1, c2, c¹3, C4, c¹5
suspension rods and the stiffening stays are led from all these points. From the
feet e, e, of the last stiffening stays from the abutment towers, perpen-
diculars d d', d, dare taken till they meet at d, d', d, d with the main
cables, and the diagonal rods d d'₁; d¹¹, d₂; d₂ d³¸
dddd
"
the points c,
intersection c, c¹, c²,
1
"
3
du
are led through
There are thus produced a series of meshes the points of
of which serve as supports for the road-way through
the medium of suspension rods and stiffening stays, and are fixed points. Through
all these points c, c, c²,
and firmly fixed to each of them, is drawn a
cable a c.
c, which I term an assembling or distributing cable and whose
ends are anchored to the abutments at the points a and b. The function of this
cable is to distribute over a large area the action of isolated loads, and to connect
all the points c, c¹, c². . so that these act practically as one long support. The
tension of this distributing cable is readily obtained by placing the tension or
tightening device employed, at the points c and c, that is to say, at the points
where the end portions of the distributing cable incline downward to be fixed to
the abutments. Finally stiffening cables a, d', and d¹¹, which are fixed at the
points a and b respectively and to the longest stays or portions o a¹ and o b¹ of the
main cables, serve to impart to these stays or portions greater rigidity than other-
wise and to prevent them from being too violently agitated by wind.
My system of construction for large structures as will be seen, is very simple
and it does not necessitate special study for each span. The longitudinal girders
are always supported at points 5" apart; the fixed points of support are all spaced
30 apart, and their height above the roadway is uniformly 10. The section of
the girders, of the suspension rods, and of the stiffening stays can thus be the same
for all the spans. The dimensions of the main cables and the stiffening stays that
lead from the abutment towers are the only one that need be calculated for
each case.
Fig. 9 illustrates a bridge having a span of 1000™ constructed according to my
system.
Fig. 10 illustrates an inclined bridge having a span of 140m. In principle,
the mode of constructing the same is the same as that of the preceding examples.
I will now give some details as to the mechanical arrangements which I employ.
As in the case of the ordinary supporting cables of suspension bridges as at
present constructed, the cables which I employ are formed of steel wire.
number and diameter of these cables will obviously depend on the length of the
spans of the structure.
The
A distinction must be made between the cables forming the parts a¹ o, o b¹ and
the parts a o, o b. The action of the permanent or isolated loads, which is exerted
at the point o (Fig. 11.) is almost exclusively borne by the first named parts
viz. a¹ o, o b¹. The other parts viz. a o, and observe as stiffening members
opposing all movement of the point o. These latter however are also subject to the
action of a part of the loads applied to the point c and c', but it will be noted that
such action is relatively small, because it can only take place to the extent
to which the parts a¹ o, o b', are subjected to a depression at the points d', d.
The cables composing the lower parts a o, and ob may therefore be less in

page_text: number or of a smaller diameter than those of the other parts a' o, o b', (see Fig. 12).
Each element of the group a' o, o b', a o, o b, is fixed by means of a tension or
tightening device to a trestle at the point of intersection o; this trestle is formed
of two rectangular frames connected together by a horizontal rod.
The suspension rod and stiffening stays meeting at the middle of the span, take
their bearing on this rod. For large structures, a similar arrangement is employed
at the points c, c¹, c²
d, d₁ d' d'₁
(Fig. 6). The rigid bars d,
ddd are each formed of two single T irons connected at their top and
bottom ends to the main cables by means of straps.
1
6
6
Each bolt at the middle e of each of these bars, serves as a fastening for the
suspension rods and stiffening stays which are maintained at the proper distance
apart by sleeves.
The points of anchorage a and b arc fixed as low as possible, and to the extent
allowed by the height of the road-way above the highest water levels for each
particular case.
Figs. 14 and 15 illustrate a very simple but strong arrangement for anchoring
the oblique cables to the piers or abutments at the points a and b. It comprises
anchors K secured in the mass of masonry of which the abutment or pier is built,
and having a slight inclination from top to bottom; frames L of angle iron that
prevent the pulling out of the anchors and which are retained in place by holding
beams M; and a bar N of round iron that passes through the ends of the anchors
and is engaged by the tightening devices connected to the lower ends of the cables.
In order to tighten the cables a¹ o, and 1 o, it is sufficient to apply at the
point o, a sufficient weight, or what is usually more simple, to exert on this point a
tractive force by means of a cable and a windlass fixed either on a ballasted boat
or on the bottom of the ravine above which the bridge extends, the force being
exerted in a perpendicular direction. For spans of 80 to 150m length, the
tightening can be effected more easily by stiffening or tightening the intermediate
parts of the cables a¹ o, bo at the same time that a downward pull is exerted
on the cables at the point o. This stiffening or tightening can be effected by
means of stays kl subjected to tension by means of an extending coupling device
acting along the line ko and located at the point o (Fig. 16). After the tightening
of the cables a¹ o, o, has been effected the tightening of the stiffening cables a o,
bo is effected. The preliminary tightening of the group of cables a¹ o, bo, is
effected as above stated, by exerting a vertical tractive force in a downward
direction on the point o; a further tightening is effected, as indicated in dotted
lines in Figs. 6 and 9, by stiffening the groups of cables by means of stays con-
nected to the cables and to the top k of a post ok located at the central point
of the bridge. Each of these stays is provided with a tension device at each
end by which the stay can be put in tension; each stay may also be placed in
tension by means of a screw-jack located at the upper end of the post o k.
The final tension will be obtained by tightening the coupling devices connected
to the main diagonal cables and forming the same into the elements d' d'1,-
d'1 d'₂-d'₂ d'3'
(see Fig. 6).
15
0
As each of these elements of the cables need not measure more than 35 to
40 metres between two successive trestles the latter tightening operation can be
easily and effectually performed.
The road-way of the bridge is composed of two side or longitudinal girders g,
(Fig. 19) transverse girders h, railings or parapet, and a flooring carried by
Zore's irons. The longitudinal girders extend the entire length of the span,
and are of uniform section being equal to that of a bridge of the same width,
between railings and of 5 length. These girders, which are slightly convex on
the upper side, may each be 0.50 to 0-60m in height according as the structure
is single or double tracked and are each supported at every 5 metres of its length
by a rod or a stay.
The transverse girders h, which may be of steel, are preferably spaced 1.50™
from axis to axis and are of I-section.

page_text: With the object of affording the greatest resistance to flexure with the minimum
amount of material and weight, the transverse girders h are made of the curved
or bent shape shown in Fig. 19.
A tie rod with caps at its ends is provided to counteract the tendency of
each transverse girder to exert, under the action of rolling loads, a lateral thrust
along the web of the longitudinal girders g, and which unless counteracted might
form a deformation of these girders. The tranverse girders are fixed to the
longitudinal ones by means of gussets where they bear directly on the lower flange
of the latter girders.
The action of wind is one of the principal causes which often tend to prevent
the erection of suspension bridges. When the gusts of wind acquire a certain
velocity, the road-way is shaken so violently that traffic thereon is rendered so
dangerous that it becomes necessary to stop it.
A bridge span constructed according to my system has, in addition to the
stiffening stays extending from the abutment towers, only a small number of
suspension rods and stiffening stays. Furthermore each portion of the main cables
may be considered as an isolated wire strung in space (Fig. 6). The entire
arrangement consequently presents but a very small surface to the action of the
wind and consequently offers a further considerable advantage over the ordinary
construction.
Finally, the construction is such as to enable the action of the wind to be
completely and very easily obviated. Thus to prevent vertical oscillations, it
suffices to connect the longitudinal girders to the points d-d,—d₂
located at the junction of the diagonal rods d, d'₁, d¹ d₁; d₁ d'₂ etc. with the
cables a o and ob (Fig. 9), by means of tie rods or small cables de-d₁ e-
which will prevent the lifting of the road-way.
d eq
The lifting of the road-way can also be prevented by means of vertical bars
or struts secured at their lower ends to the upper flanges of the longitudinal
girders and at their upper ends to horizontal rigid bars connecting each of the
points c-C₂- .
of the upstream side of the bridge, with the symmetrical
points on the downstream side. These vertical bars or struts will also ensure great
rigidity of the road-way, because being attached to the longitudinal girders and to
the fixed points C-C1-C2.
they will be subjected to a tensile force
under the action of rolling loads. They will thus act both as struts and as
suspension bars according to circumstances. Finally, they will also oppose any
distorting action which the oblique pull of the suspension rods and stiffening stays
may tend to produce upon the longitudinal girders.
One of the principal advantages of my improved construction consists in being
able to obtain as many fixed points as may be desired on the main oblique cables.
This result can only be obtained in a complete manner as long as these cables are
suitably stretched.
I have already indicated the means to be employed to obtain this tension. It
will be sufficient in order to reduce and to eliminate the effects due to an appreci-
able increase of the surrounding temperature, to employ some of these means, and
in particular, in the case of spans of usual length, to tighten the coupling device of
each cable composing the groups a¹o-b¹o only at its points of attachment with
the central trestle.
2
For large spans, the dividing up of the oblique cables enables the same effects to
be combated, since each relatively short portion d' d' d' d'₂-d'₂ d¹3..
(Fig. 9) comprised between two successive diagonal rods or trestles, can be strained
separately.
10
This straining is effected simultaneously with that of the stays k d¹, k d¹¸, k d¹¹0—
k dk dk dk dk d produced by means of a jack placed at the
upper end of the post o k, and especially by means of the coupling devices con-
necting these stays with the main cables at the points d'e, da, d'10, 12, 11, 1
11111 The tractive force or pull capable of being exerted at the points of
intersection c, C
on the rhombous shaped arrangements of diagonal
$'
6'
89

page_text: 1
acts finally to impart all
rods or cables d' d₁,-d d'₁-d'₁ d₂--d₁ d'₂ . .
desirable rigidity to the structure. Moreover, the action of the main distributing
cable a co c¹12 b fixed to all the points c-c₁₂
and to the abutments,
serves to correct the effects due to slight elongations of parts of the structure.
The posts ok at the two sides of the bridge are connected together at their
upper ends by means of a cross bar; and are stiffened against the action of wind
by means of St. Andrew's crosses.
The top k of each of these posts is connected by stays to the oblique cables at
the other side of the bridge. Thus fastened, they cannot undergo any distortion or
displacement.
The posts ok and the stiffening stays k d −k d³¸—k d¹¹ọ •
6
8
etc., also
serve to distribute the action of rolling loads. The compressing forces exerted by
these loads at the points d'-dg—d'10—d' 12—d"—d" dd, are, in part, trans-
mitted by means of the stays and posts ok, to the point o, whose resistance is very
much greater than that of the other points, since it is equal to that of the two
groups of cables a¹ 0, い。.
This transmission of the action of the load to the
central point o of the bridge has the additional advantage of further tightening the
groups of cables.
Having now particularly described and ascertained the nature of this inven
tion and in what manner the same is to be performed I declare that what I
claim is:-
1. A suspension bridge constructed with oblique cables extending from the
summits of the abutment towers and anchored at suitable points to the abutments
or piers the said oblique cables being connected together at their point of inter-
section in such a manner as to form a fixed point or support at the centre of the
span, this central point or support being equivalent to a pier and capable of being
subjected to a downward force by means of a vertical cable or otherwise substan-
tially as hereinbefore described for the purposes specified.
2. A suspension bridge of the kind referred to in the preceding claim, having
intermediate fixed points or supports such as c c¹ obtained by the intersection and
connection of small diagonal rods or cables attached to the main oblique cables, and
designed to tighten up the various elements of the bridge substantially as herein
described.
3. A suspension bridge constructed with main oblique cables connected at their
points of intersection to form a central fixed point or support; with pairs of short
diagonal rods or cables connected to the main oblique cables and connected at their
points of intersection to form intermediate fixed points or supports and with
suspension rods and stiffening stays connecting each of the said fixed points or
supports with the road-way in such a manner as to support the same at a number of
points substantially as herein described.
4. The construction of suspension bridges substantially as hereinbefore described
and illustrated in the drawings annexed.
Dated this 5th day of August 1891.
LOUIS CORMEROIS.
By L. W., per F. B.