IMPROVEMENTS IN THE CONSTRUCTION OF SUSPENSION BRIDGES
Year: 1861

page_text: LETTERS PATENT to Alphonse Oudry, of Paris, in the French Empire,
Engineer, for the Invention of "IMPROVEMENTS IN THE CONSTRUCTION OF
SUSPENSION BRIDGES."
Sealed the 23rd November 1861, and dated the 30th May 1861.
PROVISIONAL SPECIFICATION left by the said Alphonse Oudry at the
Office of the Commissioners of Patents, with his Petition, on the 30th
May 1861.
I, ALPHONSE OUDRY, of Paris, in the French Empire, Engineer, do hereby
declare the nature of the said Invention for "IMPROVEMENTS IN THE CONSTRUCTION
OF SUSPENSION BRIDGES," to be as follows:-
The main feature in my Invention consists in constructing suspension
bridges in such manner that when one portion of the platform or road is
subjected to a greater burden than other parts, it does not become distorted,
neither is the structure itself liable to oscillate. The platform of suspension
bridges as usually made is connected to one or several flexible or jointed
cables, the whole being equally balanced under the weight of the structure,
and being flexible and capable of being put out of shape, the action of an
extreme load alters the equilibrium, produces a distortion, and consequently a
fresh equilibrium. The distortion is increased in proportion to the load, and

page_text: is moreover much greater when under the immediate action of a given load
than when the strain produced by this load is spread over or made to act on
a greater portion of the span; if this strain is spread over the whole length of
the cable the distortion produced is practically nothing.
A suspension bridge although made with flexible cables would not become
distorted if the platform or floor were absolutely rigid and inflexible.
Now my Invention consists in forming each means of suspension with two
parabolic cables A, B, C, D, E, and A, B, C, D', E, as shown in the accom-
panying Drawing both in the plane of suspension, meeting at the middle
thereof as at C, and uniting into one at the pillars A and E, leaving between
them spaces A, B, C, B, and C, D, E, D, large enough to comprise all the
equilibrium curves that it would tend to take; the suspending cables are
attached to pillars sufficiently strong to maintain them at a given distance
apart. I place diagonal girders between the consecutive uprights, which in
conjunction with upright cross bars placed opposite to the parts where the
cables are brought together, and in combination with oblique girders, tend to
divide the strain, and thereby transmit to the cable least strained a portion
of the strain which would otherwise tend to be exerted on the other cable, and
by this means equalize the strain on the two cables. The plane of suspension
may be vertical or inclined so that the rods being oblique on the plane of the
platform prevent the oscillation of the latter. To prevent the swinging or
oscillation of the platform and the twisting of the rods the platform must be
as rigid as possible, and for this purpose I construct it in the following
manner: Two ribs having a lattice head form the hand rail, and cross bars by
the stop planks support the floor and the footpaths; the stop planks are made
hollow with fillings of wood, and are formed with their upper parts of T-iron.
By employing a platform as before described the suspension rods may be
further apart, two and two, three and three, for example, in the stop planks
as the case may be. In the case of large spans, I employ in the plane of the
suspension rods projecting vertically and connected together obliquely. I also
connect together in an oblique direction the suspension rods for a certain part
of their height, so as to form a species of rigid hold so as to prevent all twisting
of the suspension rods. As the twisting of the rods is produced by the sudden
action and re-action of the burdens, so it is overcome by the rigidity of the
platform or the firmness of the rods, or more properly speaking by both.
My Invention further consists in the employment of tempered cast steel for
the construction of suspension bridges, especially when the span is considerable.
The cables may be composed of jointed links. The links need not be tem-
pered except for bridges of large span, where they should be tempered

page_text: throughout, or at all events at their ends, in order to give increased resistance
to those parts hollowed out for the formation of the joints. The cables may
be also formed of blue annealed steel wire.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Alphonse Oudry in the Great Seal Patent Office on the 30th
November 1861.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, ALPHONSE
OUDRY, of Paris, in the French Empire, Engineer, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Thirtieth day of May, in the year of our Lord One
thousand eight hundred and sixty-one, in the twenty-fourth year of Her reign,
did, for Herself, Her heirs and successors, give and grant unto me, the said.
Alphonse Oudry, Her special licence that I, the said Alphonse Oudry, my
executors, administrators, and assigns, or such others as I, the said Alphonse
Oudry, exccutors, administrators, and assigns, should at any time agree
with, and no others, from time to time and at all times thereafter during the
term therein expressed, should and lawfully might make, use, exercise, and
vend, within the United Kingdom of Great Britain and Ireland, the Channel
Islands, and Isle of Man, an Invention for "IMPROVEMENTS IN THE CON-
STRUCTION OF SUSPENSION BRIDGES," upon the condition (amongst others) that I,
the said Alphonse Oudry, my executors or administrators, by an instrument
in writing under my, or their, or one of their hands and seals, should parti-
cularly describe and ascertain the nature of the said Invention, and in what
manner the same was to be performed, and cause the same to be filed in
the Great Seal Patent Office within six calendar months next and imme-
diately after the date of the said Letters Patent.
NOW KNOW YE, that I, the said Alphonse Oudry, do hereby declare the
nature of my said Invention, and in what manner the same is to be per-
formed, to be particularly described and ascertained in and by the following
statement thereof, reference being had to the Drawings hereunto annexed,
that is to say :-
My Invention consists in constructing suspension bridges in such manner

page_text: that when one portion of the platform or roadway is subjected to a greater
burthen than other portions, it does not become distorted or put out of shape,
neither is the structure itself liable to oscillate. The platforms of suspension
bridges as usually made are connected to one or several flexible or jointed
cables or chains, the whole being equally balanced under the weight of the
structure, and being flexible are capable of being put out of shape; the action
of an overload applied to one particular part of the platform alters the
equilibrium, and produces a distortion, and consequently a fresh equilibrium
has to be found. The distortion is increased in proportion as the overload is
applied to the platform of the bridge in a confined space; it is, however,
decreased in proportion as the overload is applied to a larger portion of the
length of the platform, so that if this overloading is spread over the whole
length of the platform, the primitive equilibrium will be practically main-
tained. So a suspension bridge, although made with flexible chains, would
become a rigid bridge, provided the platform was sufficiently rigid to overcome
any effect of partial or undue overloading.
My Invention further consists in preventing the suspension chains from
losing their original curve, although still flexible they will not be deranged
by an excessive or partial loading of the platform. I obtain this result by
forming a means of suspension with two parabolic chains or cables A, B, C,
D, E, and A, B, C, D, E, as shown in Figure of the accompanying
Drawing, both in the same plane of suspension, meeting in the middle as at C,
and uniting into one at the pillars A and E, leaving -between them the
spaces A, B, C, B, and C, D, E, D, large enough-to-comprise-all-variations
of the curves that each single chain would take if unduly loaded on one
particular part of the platform. These spaces are filled up by connecting rods
which maintain the chains in their relative positions. When, therefore, the
bridge is loaded upon a given point of the platform, the effort of the tension
will be to become closer to the lower chain which is immediately over the
loaded part, and to become closer to the upper chain in the corresponding
point in the other half. By the introduction of other diagonal rods in con-
junction with the herein-before mentioned connecting rods, the surplus strain
on either cable or chain will be communicated to the other, by which means
the strain will be equalized. The plane of suspension which contains the
suspension rods which connect the platform with the chains may be placed
vertically, and to prevent lateral motion to the platform they may be placed at
an angle with the plane of the platform. I make use of inclined suspension
rods on the plane of the platform, which will lead to the employment of rollers
or sectors placed on planes perpendicular to the plane of suspension, S, Figure 2,

page_text: it convenient to
being the cross section, and A, B, in Figure 2 being the plan perpendicular
to the plane of suspension. To prevent the swinging or oscillation of the
platform, and the twisting or shaking of the suspension rods, the platform
must be as rigid as possible; to obtain this rigidity I prefer to employ a
platform constructed on the system shown in Drawings Figure 20, in which
the rigidity of the lattice will allow the suspension rods to be further apart,
so that it will not be necessary to employ more than one suspension rod to
every two or three cross tie pieces, as shown in Figure 5.
When the span
or opening of the bridge is of extraordinary width, I find
use suspension rods all contained in the same plane of suspension, but some
projecting vertically and others placed obliquely connecting them together,
forming a kind of lattice or rigid whole (emsemble). If the suspension rods
all project vertically, I find it convenient to place diagonal tic pieces up to a
certain height, which add greatly to the rigidity. If four double chains are
connected together by straight rigid bars or rods maintaining the chains in their
respective planes of suspension, as seen at Figure 10, the action of the wind
coming in the direction of the arrow F¹ cannot put the chains out of their
position of equilibrium as long as the momentum of F¹ with regard to
a, b, c, d, is inferior to the sum of the momentum of weight of each of the
groups of the system of suspension, the first with regard to a', the second with
regard to C. When the platform requires to be attached close to the chains,
the cross tie pieces above mentioned cannot be employed in the middle of the
span, as they would interfero with the traffic; in this case the two double
chains on the side of the platform should be connected together, leaving the
middle space free; then each of the tie pieces, in a lattice or other form, is
firmly connected with the rigid platform; this is not shewn in the Drawings,
but is a necessity of position. In giving a convenient inclination to the planes.
of suspension, and in rendering them rigid by inserting cross tie pieces, we
may always destroy the tendency to distortion induced by a horizontal force
acting laterally on the four double chains, the line a, b, c, d, in Figure 10,
being fixed in space, and the platform being sustained on one side by the
oblique rods a, m, and b, m, and on the other side by the oblique rods c, n,
and d, n; the action of the wind in the direction of the arrow G' upon the
platform cannot force the platform on one side as long as the momentum
of G¹ with regard to a, b, c, d, is inferior to the momentum of weight of the
platform suspended in m with regard to a, and suspended in n with regard to c.
By conveniently inclining the suspension rods, that is to say, the plane of
suspension, and ballasting the platform properly, I can always render the
platform immovable under the action of the wind.

page_text: In the first part of this Specification I have shown the means by which I
can, with the aid of cables or chains, construct a suspension bridge which
cannot be put out of form. I have said that to arrive at this result it was
necessary that the two, cables A, B, C, D, E, and A, B, C, D, E, (see
Figure 14, which shows the position of the chains with the rods in zig-zag,
A and E being the points of suspension,) being disposed in a manner to
comprise all the curves of distortion or deformity which a flexible cable can
take, I maintain them in their position by vertical rods. I have also before
observed that. to transport to the portion of the cable on which there is the
least tension the excess of tension which exists on the other, it is necessary to
place oblique and diagonal rods running from the foot of one upright to the
next, and reciprocally. In this case the diagonal rods have only to resist the
tension, and all tendency to compression is destroyed by the uprights; these
may be replaced by the zig-zags, as shown in Figure 14, which, as required,
will resist sometimes tension, sometimes compression; the zig-zags may be
strengthened or stiffened by the tie picces g, Figures 11 and. 12.
I prefer
the use of steel or alloys of steel cast, tempered, hardened, or otherwise, in
erecting these suspension bridges, and cables of steel wire either tempered or
hardened, or otherwise, may be used.
Figure 1 is a Diagram of the parabolic cables; Figures 2 and 2 shew the
new system-of suspension.in longitudinal elevation and in section.; Figures 3
and-4-show-the-assemblage_or_junction of the lower links of a chain cable
with the suspension rods and the different tie pieces for a bridge of moderate
span, Figure. 3 being the side view, and Figure 4 being the plan of such
assemblage; Figure 5 is a portion of the longitudinal elevation of a bridge of
wide span, showing. the diagonal tie pieces; Figures 6 and 7 show the same
assemblage as Figures 3 and 4, but for a bridge of extraordinary span, in
which the links are made of circular section; Figures 8 and 9 the same
assemblage, but the bars are flat; Figure 10 is a transverse section of a bridge
in which four double chains of suspension are employed, and also shows the
position and disposition of the suspension rods placed obliquely to the plane
of the platform, two inclining outwards and two inwards, with cross ties in
lattice connecting together the four double chains; Figure 11 shows the
assemblage of the chains with the connecting rods in zig-zag; Figure 12 is
the section of Figure 11 at the line 1, 2; Figure 13 is the view of the zig-zig
rods seen from above; these zig-zag rods may be replaced by vertical and
diagonal rods used between two chains, as shown in Figure 2; Figure 14 is
the chain with zig-zag tie pieces; Figure 15 shows the section of a tie piece
which might be conveniently used in the zig-zags.

page_text: And having now described the nature of my said Invention, and in what
manner the same is to be performed, I declare that I claim as my improve-
ments in the construction of suspension bridges,-
First, the employment of double parabolic cables or chains, as herein-before
described and shown in the accompanying Drawings.
Second, the employment of two series of rods set obliquely to the plane of
the platform, substantially as herein-before described and shown at Figure 10
of the accompanying Drawings.
Third, the employment of rigid tie pieces to overcome the effect of a
horizontal force acting laterally upon the four double chains or systems of
suspension which would otherwise tend to deform, distort, or alter their form,
together with the means described to replace such tie pieces in the middle of
a bridge or viaduct so as not to impede the circulation, all as berein-before
described and illustrated with reference to the accompanying Drawings.
In witness whereof, I, the said Alphonse Oudry, have hereunto set my
hand and seal, this Twenty-second day of November, One thousand
eight hundred and sixty-one.
ALPHONSE OUDRY. (L.s.)