IMPROVE- MENTS IN THE CONSTRUCTION OF SUSPENSION BRIDGES AND IRON ARCHES
Year: 1872

page_text: LETTERS PATENT to Thomas Olaxton Fidler, of Emberton; in the
County of Bucks, Civil Engineer, for the Invention of "IMPROVE-
MENTS IN THE CONSTRUCTION OF SUSPENSION BRIDGES AND IRON ARCHES."
Scaled the 10th October 1872, and dated the 18th April 1872.
.
PROVISIONAL SPECIFICATION left by the said Thomas Claxton
Fidler, at the Office of the Commissioners of Patents, with his
Petition, on the 18th April 1872.
I, THOMAS CLAXTON FIDLER, of Emberton, in the County of Bucks,
Civil Engineer, do hereby declare the nature of my said Invention for
"IMPROVEMENTS IN THE CONSTRUCTION OF SUSPENSION BRIDGES AND IRON
ARCHES," to be as follows:-
This Invention relates to certain improvements in the construction
of suspension bridges and iron arches, whereby the chains or ropes of a
suspension bridge are so arranged and braced together that they offer a
firm and inflexible support to a passing load and carry it without the.
distortion and oscillations common to ordinary suspension bridges. To
effect this I employ in the place of a single chain two chains which are
attached together or to the same saddle upon each pier or abutment, but

page_text: hang across the opening in different curves, crossing each other in the
centre of the span; the upper chain of each half span should lie in a
straight inclined line, and the lower chain in a parabolic or other curve
to which the upper chain of the other half forms a tangent. The chains
may be pinned together or attached to the same centre link at the point
of their intersection. The upper and lower chains are braced together
by diagonal bracing. The effect of irregular loading is however
principally taken up not by the bracing but by. the chains themselves.
When one half of the span is uniformly weighted and the other half
entirely without weight, the load is carried by the lower chain of the
weighted half and the upper chain of the other half, which together form
one continuous chain of such form as to be in equilibrium under that
load. The weight of the straight upper chain of the unloaded half and
the rest of the weight of that half is carried in like manner by the upper
chain of the loaded half and the lower chain of the unloaded half.
When only a part of either half span is loaded the effect of that
irregularity of load is taken up by the bracing.
In applying this Invention to the construction of arches of wrought
or cast-iron each rib is hinged at the abutments and at the crown; each
half rib has an upper and a lower flange which lie close together at the
crown and at the abutments, and are more widely separated between
those points, the lower flange being straight from abutment to crown or
only slightly arched, and the upper flange being more sharply arched
and so arranged that the upper flange of one half rib approaches the
centre hinge in the same line with the lower flange of the other half rib
or nearly so.
The web between the two flanges may be of plate, or lattice, or other
bracing. In the same way the suspension bridge may consist of two
inverted half ribs hinged together at the centre, and hinged to the
saddles upon the piers and built of plate and angle iron.
A suspension bridge constructed according to this Invention may
have a side span on each side of the centre span, and each of such side
spans may be carried by a pair of braced chains similar to one half span
of the centre opening.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Thomas Claxton Fidler in the Great Seal Patent
Office on the 16th October 1872.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, THOMAS
CLAXTON FIDLER, of Emberton, in the County of Bucks, Civil Engineer,
send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Eighteenth day of April, in the year
of our Lord One thousand eight hundred and seventy-two, in the thirty-
fifth year of Her reign, did, for Herself, Her heirs and successors, give
and grant unto me, the said Thomas Claxton Fidler, Her special license
that I, the said Thomas Claxton Fidler; my executors, administrators,
and assigns, or such others as I, the said Thomas Claxton Fidler,
my exécutors, administrators, or 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 CONSTRUCTION OF SUSPENSION BRIDGES AND IRON ARCHES," upon the
condition (amongst others) that I, the said Thomas Claxton Fidler, my
executors or administrators, by an instrument in writing under my
hand and seal, should particularly 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 immediately after the date of the said
Letters Patent..
NOW KNOW YE, that I, the said Thomas Claxton Fidler, do hereby
declare the nature of my said Invention, and in what manner the
same is to be performed, to be particularly described and ascertained
in and by the following statement, reference being had to the accom-
panying Drawings, and to the letters and figures marked thereon, that is
to say:-
My said Invention consists in a method of constructing suspension
bridges whereby the chains are so arranged and braced as to afford an
inflexible support to the roadway and to carry a passing load without
distortion.

page_text: And in order that my said Invention may be fully understood I shall
now proceed more particuarly to describe the same, and for that purpose
shall refer to the several Figures on the annexed Sheet of Drawings, the
same letters of reference indicating corresponding parts in all the
corresponding Figures.
66
a,"
"
Figure 1 of my Drawings is an elevation of a suspension bridge
constructed according to my said Invention. ," "a," are the piers,
and "b, b," the land ties. In the place of a single chain from “c”
to "h" I employ two chains represented by the lines "c, d, e, f, g, h,”
and “c, i, k, f, m, h," which are attached together or to the same saddle 1
at "c" and "h,” and cross each other at "f"; tho line “c, i, k, f," is
a parabolic curve, and the line "f, m, h," is a straight line which forms
a tangent to that curve at "f"; in like manner the chain "f, g, h,"
lies in a parabolic curve, and the chain "c, d, e, f,” in a straight line,
which forms a tangent to that curve at the point "f." The chains are 1
united by the vertical struts "d, i, e, k," &c., and by the diagonal
braces d, k, i, e, &c. The roadway r, r, is attached to the chains by
the rods i, r, k, r, &c. If the half span c, f, is uniformly loaded the
load is carried by the chain "c, i, k, f, m, h," which forms a line of
equilibrium for that load, quite independently of what load there may
be upon the other half span. In like manner the chain “c, d, e, f, g, h,”
is in equilibrium under any uniform load upon the half span f, h, so
that each chain is under a uniform horizontal tension throughout its
length so long as the two half spans are uniformly loaded, though the
load on one half may be greater than the load on the other half, and :
the braces have no strain upon them.
When either half span is only partially loaded the bracing is strained
and prevents any distortion of the chains, the chains and bracing
together forming a rigid inverted bowstring rib. The bracing acting
in this way increases the strain in certain parts of the chains and
lessens it in other parts, and I make the sectional area of the chains
proportional to the greatest strain; that is to say, the upper chain has
a greater area near the piers and less near the centre, and the sectional
area of the lower chain is proportional to the secant of the angle of
inclination at its different parts, just as in an ordinary suspension chain, ¦
because the greatest horizontal strain is the same for every bar of the
lower chain, and is nearly equal to the horizontal strain of the upper

page_text: chain at "f" but less than the greatest horizontal strain in the upper
chains at "c" and "h.”
'In bridges of large span where the live load bears a small proportion
to the dead load, the diminution of tension caused by an irregular
loading of either half span is not great, and I construct the chains
of such bridges in any ordinary method, as shewn in Figure 2, which is
a cross section of the inverted bowstring rib formed by one half of the
bridge. "a" is the upper chain; "b," the lower chain; and "c" is a
vertical strut braced to resist compression.
66
In bridges where the live load bears a great proportion to the dead
load the upper chain may
at certain points be thrown into compression;
therefore in small bridges I substitute a rigid plate structure in place
of the upper chain, as shewn in the cross section, Figure 4, where the
upper chain is replaced by the plates "and angle irons "b," which
5 are capable of resisting either tension or compression.
"d" is the lower
chain, and "C" is a vertical strut built of plate and angle irons. The
differences of strain caused by the said irregular loading are less when
the upper chain is straight than when it hangs in a curve, therefore I
construct all suspension bridges with the upper chain straight.
)
My Invention consists further in the construction of iron arches upon
the same principle. Figure 4 is an elevation of such an arch, consisting
of two half ribs “a, b," and "b, c," hinged at the abutments " "a"
and "c," and hinged together at the crown "b." Each half rib has an
upper flange "a, d, b," sharply curved, and a lower flange "a, e, b,”
5 less sharply curved or straight; the flanges meet at "a" and at "b,"
"
and are united in the middle by a plate or lattice web "h," and the
flanges are so arranged that the upper flange "d, b," meets the
centre "6" in the same line with the flange "b, g."
The principles before stated as applying to the suspension bridge
O apply also to the arch, with the difference that the flanges are in
compression instead of in tension; a certain irregularity of loading.
might throw the lower flange "a, e, b," into tension, but as this is of
no consequence the lower flange may be curved and not straight.
Figure 5 is a cross section of an arch rib of wrought iron, the upper
3 flange "a, b," and the lower flange "d, e," being built of plate and
angle iron, united by the plate or lattice web "c."

page_text: Figure 6 is a cross section of an arch rib of cast iron in which the
flanges "a" and "b" and the web "c" are cast in one piece. The
suspension bridge may also have the cross section shewn in Figure 5
or 6, and may be constructed exactly as the arch inverted.
The half ribs of the suspension bridge are in any case either actually
or virtually hinged to the piers at "c" and "" Figure 1, and hinged
together at "f"
The upper and lower chains or flanges may be actually hinged
together and with the saddle at "h," or the two chains may be
separately attached to the saddle, as shewn in Figure 7, in which “ "a, d,"
is a bar of the upper chain, "b, c," a bar of the lower chain, attached
by the pins "a" and "6" to the saddle plates "e." The pins "a"
and "b" are placed in the line of the bar "b, c," so that a small angular
motion of the whole half rib would produce no sensible strain upon
either bar. In the same way the two half ribs may be actually hinged
together at "f," Figure 1, or the two chains may cross each other, the
flat links of one chain passing between those of the other chain, or the
upper and lower chain of each half rib may be separately attached to
junction plates, as shewn in Figure 8, in which "p" is the junction
plate to which are attached the chains "a, b," and "e, f," of the left
half rib, and the upper chain g, h, n, and lower chain“ c, d, o," of the
right half rib, the centres "b, c, f, and "g" being arranged in the
lines of the bars, or nearly so, in the same way as in Figure 7; i is a
vertical strut in the right half rib, and "k, k," the diagonal braces
cottered up to an adjusting plate m.
Having now described and particularly ascertained the nature of my
said Invention, and the manner in which the same is or may be used or
carried into effect, I would observe in conclusion that what I consider
to be novel and original, and therefore claim as the Invention secured
to me by the herein-before in part recited Letters Patent is,―
1st. The application and use to and in the construction of suspension
bridges of two chains attached to the same saddles, each chain hanging
across one half of the span over the other chain in a straight inclined
line, and across the other half of the span under the other chain in a
parabolic curve to which the first half forms a tangent, the two chains
being braced together, as berein-before described and illustrated in
Figure 1 of my Drawings.

page_text: 2ndly. The employment of a plate built rigid member in place of the
straight upper chain of this system, as and for the purpose herein-before
described and illustrated in Figure 3 of my Drawings.
.
3rdly. The construction of the whole of each rib of a suspension
bridge, such as is above referred to, in plate and angle iron, the ribs
being hinged together at the centre and hinged to the piers or saddles,
substantially as herein-before described.
4thly. The construction of wrought and cast iron arches in two half
ribs hinged to each other and to the abutments, the flanges of the ribs
being arranged in lines meeting at the abutments and at the crown, and
crossing each other at the crown, as herein-before described and illus-
trated in Figure 4 of my Drawings.
In witness whereof, I, the said Thomas Claxton Fidler, have to
this my Specification, set my hand and seal, the Eighth day of
October One thousand eight hundred and seventy-two.
THOMAS CLAXTON FIDLER. (L.S.)
Witness to the execution hereof,
by the above-named Thomas
Claxton Fidler,
JOHN GABBARD,
Sol.,
Olney.