IMPROVEMENTS IN THE CON- STRUCTION OF BRIDGES AND ROOFS
Year: 1873

page_text: LETTERS PATENT to Alfred Vincent Newton, of the Office for Patents,
66, Chancery Lane, in the County of Middlesex, Mechanical
Draughtsman, for the Invention of "IMPROVEMENTS IN
THE CON-
STRUCTION OF BRIDGES AND ROOFS."-A communication from abroad by
James Buchanan Eads, of St. Louis, in the State of Missouri,
United States of America.
PROVISIONAL SPECIFICATION left by the said Alfred Vincent Newton
at the Office of the Commissioners of Patents, with his Petition, on
the 4th November 1873.
I, ALFRED VINCENT NEWTON, of the Office for Patents, 66, Chancery
Lane, in the County of Middlesex, Mechanical Draughtsman, do hereby
declare the nature of the said Invention for "IMPROVEMENTS IN THE
CONSTRUCTION OF BRIDGES AND Roors," to be as follows:-
+
The object of this Invention is to improve the construction of arched
bridges and roof by enabling the horizontal thrust due to the weight of
such structures to be distributed in any desired proportion between the

page_text: abutments and the horizontal member or members forming a tie or ties
between the springings of the arch; also in the case of a series of arches
or spans to so arrange the horizontal members or chords above men-
tioned that the unbalanced horizontal force due to the loading of any
one span is partly resisted by the chord of that span and partly trans-
mitted to the abutments by the chords of the other spans.
Further, the Invention includes a means of so connecting the chords
of a series of arched spans that their action is not interfered with by
changes of temperature.
In applying the Invention to a single arched span, one end (hereafter
called for convenience the "fixed end") abuts against the skewbacks
of one of the abutments as usual, while the other end abuts against some
intermediate point in a lever situated at the other abutment. One end
of this lever is connected to the abutment on which the lever is situated,
and the other to a suitable horizontal member or chord extending to the
skewbacks against which the arched rib abuts at its fixed end. The
effect of this arrangement necessarily is that according to the proportion
between the two arms of the interposed lever so will the thrust of the
arched rib be distributed between the abutments and the horizontal
member or chord. In applying this system to two spans, the fixed end
of each rib bears against the abutment as usual, while the ends resting
on the intermediate pier abut against the opposite point of a lover which
also receives the thrust in the opposite direction of the adjoining span.
The ends of this lever are respectively connected to the chords or hori-
zontal members of the two spans. So long as the two spans are of
cqual dimensions and are equally loaded, the horizontal forces at the
intermediate pier balance each other, and no strain is thrown upon the
chords. If however one span be loaded and the other unloaded then the
unbalanced thrust so created is borne partly by the chord of the arch so
loaded (this chord being put in tension), and is partly transmitted by
the chord of the other arch to the abutment belonging to that arch; the
chord thus transmitting this strain being of course placed in com-
pression. If the two spans are of unequal size, the horizontal forces due
to the unequal thrust of the arches and to the unequal loading may be
distributed in any desired proportion between the two chords by varying
the proportions of the arms of the lever on the intermediate pier, and in
any case the lever on the intermediate pier may, if desired, be so fixed
to that pier as to cause some portion of the unbalanced horizontal thrust

page_text: to be thrown upon the latter instead of being wholly taken up by the
chords and shore abutments.
It is evident that in the arrangement above described the expansion
or contraction of the chords will merely cause the lever on the inter-
mediate pier to turn in one direction or the other on the centre against
which the the arched ribs abut, and will not in any way modify the
distribution of the strains.
In applying the system to bridges or roofs of more than two spans
several modified arrangements may be adopted. According to one plan
the whole of the adjustment required by the expansion and contraction
of the chords under changes of temperature is effected on one inter-
mediate pier, that pier carrying and adjusting lever for cach line of
chords, and the chords extending from the two shore of fixed abutments
being connected to the opposite ends of that lever, while the adjoining
arched ribs abut against an intermediate point or fulcrum as in the
arrangement above explained. If the adjusting lever now referred to be
situated at the centre of the length of the bridge it will have equal
arms, otherwise the length of its arms will be directly proportioned to
the lengths of the lines of chords to which they are attached. Thus, if
in a bridge of five equal spans the equalizing levers are placed on the
second pier from one shore, the arms of these levers will be in the pro-
portion of three to two, the line of chords procceding from the nearest
abutment being coupled to the shortest arms.
According to another arrangement each intermediate pier is provided
for each arched rib with an equalizing lever having equal arms against
an intermediate point (called hereafter the fulcrum) of which the adjacent
arched ribs abut. In the case of the lever on the first pier from the.
shore, the one end is connected by a chord with the skew backs of the
adjacent shore abutments while the other end is similarly connected with
pier No. 2. In the case of the lever on pier No. 2, one end is connected
by a chord with the fulcrum of the lever on pier No. 1, while the other
end is connected by a similar chord to pier No. 3, and so on.
According to a third modification the intermediate piers are provided
with equalizing levers having arms, the relative lengths of which in the
case of any one pier are proportional to the distances of that pier from
the two shore abutments. Thus in the case of a bridge having four
equal spans the levers on the central pier would have equal arms, while

page_text: those on the two side piers would have arms with the proportion of
three to one.
In this arrangement as in the other the arched ribs abut
against the fulcrum of the levers, while the two ends of the latter are
coupled to two systems of chords which start respectively from the two
shore abutments, and each of which extends for the whole length of the
bridge, less one span.
Referring again to the supposed example of a four span bridgo just
mentioned, the line of chords springing from each abutment would be
attached to the shorter arm of the lever on the nearest pier to one of the
equal arms of the lever on the middle pier, and to the longer arm of the
lever on the most distant pier, at which point the line of chords would
stop. The arched ribs of the shore spans of such a series as that just
mentioned will evidently be in the same condition as the ribs of the two
span bridge considered above, while in the case of the intermediate
spans as the ribs abut against the fulcra of the levers it is evident
that a portion of the unbalanced horizontal thrust due to the loading of
any arch singly will be resisted partly by a tensional strain set up on the
chords of that span, and will partly be transmitted as a thrust to the
shore abutments through the intervention of the chords of the adjoining
span. It is evident that in this arrangement the lengths of the arms of
the levers on the intermediate piers being proportionate to the length of
the chords connecting them to the shore abutments, any expansion or
contraction of the chords will merely cause the levers to turn on their
fulcra, and will put no horizontal strain on the intermediate piers. If
desired however the latter may be so connected with the levers that they
may be caused to assist the chords in taking up a portion of the hori-
zontal strain due to unequal loading of the spans. When the levers are
not so connected to the piers the latter have to act merely as columns to
support vertical pressure, and they may therefore be made materially
lighter than is required in the case of ordinary arched bridges.
In carrying out my Invention, particularly when applied to large
spans, it is desirable that the horizontal chords should serve as the
tension and compression members of the wind bracing of their respective
spans. To enable them to do this more effectually when the bridge
consists of two or more spans I so connect the levers belonging to the
chords on the opposite sides of the bridge that the ends of the chords
adjacent to each other cannot approach or withdraw from each other over
any one pier unless the chords on the opposite side of the bridge undergo a

page_text: similar movement over the same pier. Thus to take the case of a two
span bridge having each span composed of two arched ribs with two
corresponding horizontal chords which also form members of the wind
bracing, in such a bridge the lateral pressure of the wind would place
the chords on the windward side in compression, and those on the
leeward side in tension; and thus if no means were adopted to prevent
it the ends of the two chords on the windward side would withdraw
from each other at the central pier, while those on the leeward side
would approach each other. According to this part of the Invention
the equalizing levers of the windward and leeward chords are so con-
nected by an intermediate lever or lever and transverse links that any
motion of one tending to produce an approach of the ends of the chords
to which it belongs cannot take place without the occurrence of a similar
movement in the lever belonging to the chords on the other side of the
bridge. The effect of this is that while the expansion and contraction of
the chords is not interfered with, these chords are nevertheless practically
made continuous over the piers, and the system of wind bracing of
adjoining spans thus gains the additional resisting power due to con-
tinuity.
It is evident that the various modes above described of carrying out
the Invention or any mere modification of them may, if desired, be
combined in a single structure, and it is further evident that in a bridge.
or roof of several spans any intermediate pier may, if desirable, be
treated as an abutment pier and be treated in the same way as the shore
abutments above referred to.
It is preferred in carrying out the above plans that the arched ribs
employed should be hinged at the crowns and springings. The levers
referred to above as the equalizing levers may be arranged to oscillate in
a vertical, horizontal, or any intermediate plane, as may be desirable.
O SPECIFICATION in pursuance of the conditions of the Letters Patent
filed by the said Alfred Vincent Newton in the Great Seal Patent
Office on the 4th May 1874.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, ALFRED
VINCENT NEWTON, of the Office for Patents, 66, Chancery Lane, in the
5 County of Middlesex, Mechanical Draughtsman, send greeting.

page_text: WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Fourth day of November, in the year
of our Lord One thousand eight hundred and seventy-three, in the
thirty-seventh year of Her reign, did, for Herself, Her heirs and successors,
give and grant unto me, the said Alfred Vincent Newton, Her special
license that I, the said Alfred Vincent Newton, my executors, adminis-
trators, and assigns, or such others as I, the said Alfred Vincent Newton,
my executors, 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 CONSTRUCTION OF BRIDGES AND ROOFS," being a com-
munication to me from abroad by James Buchanan Eads, of St. Louis,
in the State of Missouri, United States of America, upon the condition
(amongst others) that I, the said Alfred Vincent Newton, my executors
or administrators, by an instrument in writing, under my, or their, or
one of their hands and seals, 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 Alfred Vincent Newton, do hereby
declare the nature of the 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 Drawing here-
unto annexed and to the letters and figures, marked thercon (that is to
say) :-
The object of this Invention is to improve the construction of arched
bridges and roofs by enabling the horizontal thrust due to the weight of
such structure to be distributed in any desired proportion between the
abutments and the horizontal member or members forming a tie or ties
between the openings of the arch; also in the case of a series of arches
or spans to so arrange the horizontal members or chords above mentioned
that the unbalanced horizontal force due to the loading of any one span
is partly resisted by the chord of that span and partly transmitted to the
abutments by the chords of the other spans.

page_text: Further, the Invention includes means of so connecting the chords of
a scries of arched spans that their action is not interfered with by
changes of temperature, and they are caused to distribute the lateral
strain due to the pressure of the wind.
In applying the Invention to a single arched span, one end (hereafter
called for convenience the fixed end) abuts against the skewbacks of
one of the abutments as usual, while the other end abuts against some
intermediate point in a lever situated at the other abutment. One end
of this lever is connected to the abutment on which the lever is situated
and the other to a suitable horizontal member or chord extending to the
skewbacks against which the arched rib abuts at its fixed end.
In the accompanying Drawing this arrangement is illustrated in the
diagram plan at Fig. 1, and in elevation at Fig. 2.
A and B are the abutments of the arch; A¹ is the skewback against
which the fixed ends of the arched ribs C, C, abut, and B¹ is the skew-
back of the abutment B. D, D, are levers pivotted to the free ends of
the arched ribs C, C; these levers are severally connected at their outer
ends by the chords or tie rods E, E, to the skewback A', and they are
similarly connected at their inner ends by brackets F, F, to the skew-
back B¹. The effect of this arrangement is that according to the pro-
portionate length of the two arms of the interposed levers D so will the
thrust of the arched ribs C be distributed between the abutments by or
through the tie rods. In applying this system to two spans, the shore
ends of the ribs bear against the shore abutments as usual, while the
opposite ends of these ribs rest on the intermediate pier and abut against
the intermediate point of a lever which serves to distribute the thrust in
opposite directions. This arrangement is illustrated in the diagram
plan Fig. 3, where A, A', are the shore abutments; B, B, are the arched
ribs, and C the intermediate pier; D is the lever and E, E, the rods or
chords which connect the opposite ends of the lever to the shore
abutments; it will now be understood that as long as the two spans are
of equal dimensions and are equally loaded the horizontal forces at the
intermediate pier will balance each other, and no strain is thrown upon
the chords. If however one span be loaded and the other unloaded then
the unbalanced thrust so created is borne partly by the chord of the
archi so loaded (this chord being put in tension), and is partly transmitted
by the chord of the other arch to the abutment belonging to that arch,

page_text: the chord thus transmitting this strain being of course placed in com-
pression. If the two spans are of unequal size the horizontal forces due
to the unequal thrust of the arches and to the unequal loading may be
distributed in any desired proportion between the two chords by varying
the proportions of the arms of the lever on the intermediate pier, and in
any case the lever on the intermediate may, if desired, be so con-
nected to that pier as to cause some portion of the unbalanced horizontal
thrust to be thrown upon the latter instead of being wholly taken up by
the chords and shore abutments. One mode of attaining such an end
would be by causing the arches to abut, not on the fulcrum of the
compensating lever chord, but on some intermediate point in a lever
connecting that fulcrum with the pier. The ratio of the two arms of
this connecting lever as it may be termed would fix the proportions
of the thrust transmitted to the chords and the intermediate pier
respectively.
It is evident that in the arrangements above described the expansion
or contraction of the chords will merely cause the lever on the inter-
mediate pier to turn in one direction or the other on the centre against
which the arched ribs abut, and will not in any way modify the dis-
tribution of the strains.
In applying the system to bridges or roofs of more than two spans
several modified arrangements may be adopted. According to one plan
the whole of the adjustment required by the expansion and contraction
of the chords under changes of temperature is effected on one inter-
mediate pier, that pier carrying an adjusting lever for each line of
chords, and the chords extending from the two shore or fixed abutments
being connected to the opposite ends of that lever while the adjoining
arched ribs abut against an intermediate point or fulcrum as in the
arrangement above explained. If the adjusting lever now referred to be
situated at the centre of the length of the bridge it will have equal arms,
otherwise the length of its arms will be directly proportioned to the
lengths of the lines of chords to which they are attached. Thus if in a
bridge of five equal spans the equalizing levers are placed on the second
pier from one shore, the arms of these levers will be in the proportion of
three to two, the line of chords proceeding from the nearest abutment
being coupled to the shortest arms. This arrangement is illustrated by
the diagram Fig. 4, where D, D, are the compensating levers connected
at their opposite ends by the tie rods E, E, to the shore abutments A, A¹.

page_text: however the latter may be so connected with the levers that they may
be caused to assist the chords in taking up a portion of the horizontal
strain due to unequal loading of the spans, as explained, when speaking
of the two-span bridge. When the levers are not so connected to the
piers the latter have to act merely as columns to support vertical
pressure, and they may therefore be made materially lighter than is
required in the case of ordinary arched bridges.
In the case of four arches the plan first described for two arches can
be used, but the middle pier of the series must in that case be capable of
resisting the whole thrust of the load; for if two spans on one side be
loaded the chords of the other two unloaded spans will not assist at all.
The unloaded arches on one side of the centre pier however balance the
thrust due to the dead weight of the arches on the other side so that the
pier has to resist the thrust due to the load only. The abutments on
the other hand must be able to resist the entire thrust due to the live
and dead loads in all cases when there are two or more spans, but in the
case of a single arch bridge the circumstances are different, it being in
such a case possible to divide the thrust in any desired proportions
between the chord and the abutments. A load on both spans of the two-
span bridge puts a tensional strain on both chords if the abutments do
not sustain the whole thrust, and this the levers would not resist.
In carrying out this Invention, particularly when applied to large
spans, it is desirable that the horizontal chords should serve as the
tension and compression members of the wind bracing of their respective
spans. To enable them to do this more effectually when the bridge
consists of two or more spans, I so connect the levers belonging to the
chords on the opposite sides of the bridge that the ends of the chords
adjacent to each other cannot approach or withdraw from each other
over any one pier unless the chords on the opposite side of the bridge
undergo a similar movement over the same pier. This is illustrated at
Fig. 6 as applied to a two-span bridge having each span composed of
two arched ribs with two corresponding horizontal chords which also
form members of the wind bracing, in such a bridge the lateral pressure
of the wind would place the chords on the windward side in compression
and those on the leeward side in tension; and thus if no means were
adopted to prevent it the ends of the two chords on the windward side
would withdraw from each other at the central pier, while those on the
leeward side would approach each other. According to this part of the

page_text: Invention the equalizing levers D, D, of the windward and leeward
chords E, E, are so connected by an intermediate lever, or lever and
transverse links D₁, that no motion having a tendency to produce an
approach of the ends of the chords to which it belongs can take place
without the occurrence of a similar movement in the lever belonging to
the chords on the other side of the bridge. The effect of this is that
while the expansion and contraction of the chords is not interfered with
these cords are nevertheless practically made continuous over the piers,
and the system of wind bracing of adjoining spans thus gains the
additional resisting power due to continuity. This effect of continuity
may likewise be secured by connecting the chords, as described, to
vertical equalizing levers at each intermediate pier, and fixing these
levers one at each end of a shaft carried by suitable bearings fixed to the
pier, this shaft having a position transverse to the roadway. The chords
from one abutment would be fastened to the upper ends of these levers,
while the chords from the other abutment would be fastened to the
lower ends. It is manifest that with this arrangement the ends of the
chords on one side of the pier could not be separated or brought nearer
together without causing a partial rotation of the shaft, and this rotation
would ensure a similar movement on the chords on the other side of the
pier. In all cases the arches may abut against the fulcra of the levers,
or the piers themselves of the fulcra be properly secured to the latter.
It is evident that the various modes above described of carrying out
the Invention, or any mere modification of them may, if desired, be
combined in a single structure, and it is further evident that in a bridge
or roof of several spans any intermediate pier may, if desirable, be
treated as an abutment pier, and be treated in the same way as the shore
abutments above referred to.
It is preferred in carrying out the above plans that the arched ribs
employed should be hinged at the crowns and springings. The levers
referred to above as the equalizing or compensating levers may be
arranged to oscillate in a vertical, horizontal, or any intermediate plane
as may be desirable.
Having now set forth the nature of the Invention of "Improvements
in the Construction of Bridges and Roofs," as communicated to me by
my foreign correspondent, and explained the manner of carrying the
same into effect, I wish it to be understood that under the above in part
recited Letters Patent I claim,―

page_text: First. Distributing the strain due to both vertical and lateral pressure
throughout the arched structure, in the manner and for the purpose
above described.
Second. Constructing the metal chords of arches in roofs and bridges
with equalizing joints, as described, whereby the expansion and con-
traction of the chords caused by variations of temperature may be
accommodated between the abutments and piers in a manner to avoid
the increase of the tensile or compressive strains in said chords.
In witness whereof, I, the said Alfred Vincent Newton, have
hereunto set my hand and seal, the Fourth day of May, in
the year of our Lord One thousand eight hundred and seventy-
four.