IMPROVEMENTS IN BRIDGES
Year: 1873

page_text: LETTERS PATENT to William Edward Newton, of the Office for
Patents, 66, Chancery Lane, in the County of Middlesex, Civil
Engineer, for the Invention of "IMPROVEMENTS IN BRIDGES."-A com-
munication from abroad by James Buchanan Eads, of St. Louis,
Sealed the 3rd March 1874, and dated the 12th September 1873.
PROVISIONAL SPECIFICATION left by the said William Edward Newton
at the Office of the Commissioners of Patents, with his Petition, on
the 12th September 1873.
I, WILLIAM EDWARD NEWTON, of the Office for Patents, 66, Chancery
Lane, in the County of Middlesex, Civil Engineer, do hereby declare the
nature of the said Invention for "IMPROVEMENTS IN BRIDGES," to be as
follows:-
This Invention relates to improvements in the construction of the
superstructure of arched bridges.
It relates, first, to a novel method of constructing and trussing or
stiffening the arches of bridges, so as to enable them to resist the changes

page_text: of form induced by unequal loading, and to bear the changes of
temperature without being strained thereby. This is effected by con-
necting the inner or central ends of each half of the arch by a suitable
joint at the crown, and stiffening each half arch by a counter arch
connected to its ends, namely at the abutment, and also at the crown.
As a modification, the counter arches may be connected at their inner
ends to the main arch, and at their outer ends to the abutment. The
counter arches are inverted, and are connected to the main arch by
suitable bracing between them and the main arch.
The Invention relates, secondly, to a novel method of relieving the
central piers of bridges from the unequal thrust of the arches caused by
the unequal loading of the same. This is effected by making the
roadway substantially continuous against compressive strain from the
abutment at one end of the bridge to the abutment at the other end of
the bridge, so as to bring the horizontal strain of all the arches ultimately
on the said abutments.
. The roadway may also be made continuous in such manner as to
resist tensional strains from pier to pier or abutment, and thus lessen
the compressive strains that would otherwise come against the abutments.
This is effected by the use of tension members or distance pieces arranged
as chords of the arc. These chords or distance pieces are screwed up at
each end to skew backs at the piers or abutments, and likewise serve for
wind trussing or bracing. Tension or compression screws are made to
bear against the outer side of the skew backs, and act in tension or
compressively against the ends of the chords or distance pieces.
In reference to this method of relieving the piers which support a
series of arched spans from the horizontal component of the thrust of
said arches, let us suppose that two spans constitute a bridge, and the
shore abutments alone are constructed of sufficient strength to resist the
thrust of the arches with their loads. If the loads be equal and the
arches are of the same form and weight, the thrust of one span against
the central pier will be balanced by the thrust of the other, and a pier
or column simply calculated to sustain the vertical pressure, as in
ordinary trusses would be sufficient to insure stability; but if the load
be removed from one span the pier will be overturned by the thrust of
the loaded one. To prevent this overthrow of the piers by such
horizontal force without the expense of increasing the size and weight of

page_text: the piers, the chords of the wind trussing are made to form the roadway.
This roadway and such other longitudinal members of the roadway as
may
be necessary are formed of some non-expansible material (wood for
instance), and these chords and longitudinal members are abutted
against the abutments and piers in or about the line of the springing of
the arches, so as to cause the chords and members aforesaid in the
unloaded arches to resist by their compressive strength the horizontal
force resulting from the loading of any other arch in the system. These
distance pieces or chords in any one arch will not be in compression at
the time the load is borne by that particular arch, except when initial
compression is produced in them; but if they were firmly secured to the
piers or pier and abutments supporting the arch so as to resist tension,
and were constructed throughout their length so as to resist tension, it
will be seen at once that the compressive strain thrown on the chords in
the other (unloaded) arches would be lessened by the amount of tension
borne by the chords in the loaded arch.
When an arch is loaded the distance pieces in the other arches will
be compressed, and consequently slightly shortened. This will have the
effect of slightly changing the positions of the tops of the piers, and if
this change be so great as to endanger the stability of the piers, the
longitudinal movement of the bases of the arches may be accommodated
by arranging the skew backs or bed plate to slide on the tops of the
piers after the manner of ordinary trusses, in which case the distance
pieces would abut against the skew backs (or screws).
Where several arches constitute a series of spans, and the load be on
one span, the extent of shortening in all of the chords of the unloaded
spans from the horizontal force of the load may cause the bases of the
loaded arch to move so far apart as to cause objectionable deflection in
that arch. To prevent this stronger abutments are provided, and
adjusting screws are fixed at the skew backs of each arch to act against
the distance pieces in such manner as to produce a compressive strain
throughout the entire line of chords from abutment to abutment when
the bridge is unloaded. This initial compressive strain may be produced
to such an extent (by calculation) as to be just sufficient to relieve the
chords of an arch entirely of compressive strain when bearing the
maximum load, and yet not produce tension in it. In this case the
deflection of that arch will be limited by the compression in the arch

page_text: itself, due to the load, and by the separation of the arch bases to the
extent of the initial compression in its own chords or distance pieces.
In a series (for instance) of five arches of say five hundred feet span,
where the maximum horizontal force produced by the load on one arch
equals 500 tons if an initial compressive strain of 400 tons be produced
in the entire system of chords from abutment to abutment by the
screws when the bridge is unloaded, then this initial strain will be taken
out of the chords of an arch next the abutment so soon as it bears its
maximum load, while the compressive strain in the remaining chords
will be proportionately increased.
When all the arches are loaded, the strain on the abutments will be
500 tons, plus 400 tons, plus the horizontal force of the unloaded arches,
say 300 tons, making a total of 1,200 tons. This system is applicable
to all of the ordinary forms of truss bridges also, and by it the usual fron
chords or tension members of a series of trusses may be dispensed with,
and wooden compression members or chords substituted, thus effecting
an important saving in cost.
It must be borne in mind that as each arch in an uniform system
balances the thrust of its neighbour, the horizontal force against the
abutments remains the same, whether there be one arch or any greater
number of arches in the same series. The same remark applies to trusses
also.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said William Edward Newton in the Great Seal Patent
Office on the 12th March 1874.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, WILLIAM
EDWARD NEWTON, of the Office for Patents, 66, Chancery Lane; in the
County of Middlesex, Civil Engineer, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Twelfth day of September, 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 William Edward Newton, Her special
licence that I, the said William Edward Newton, my executors, admi-

page_text: nistrators, and assigns, or such others as I, the said William Edward
Newton, my executors, administrators, and assigns, should at any time
agree with, and no others, from time to time and at all times there-
after 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 Inven-
tion for "IMPROVEMENTS IN BRIDGES," being a communication to me from
abroad by James Buchanan Eads, of Saint Louis, in the State of
Missouri, United States of America, upon the condition (amongst others)
that I, the said William Edward 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 William Edward 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 thereon (that is
to say):-
This Invention relates to improvements in the construction of the
superstructure of arched bridges.
It relates firstly to a novel method of constructing and trussing or
stiffening the arches of bridges so as to enable them to resist the changes
of form induced by unequal loading and to bear the changes of tempera-
ture without being strained thereby. These objects are effected by
connecting the ends of the arch by a suitable joint at the crown and
stiffening each half arch by a counter arch connected to its ends, namely,
at the abutment and also at the crown. The counter arches are inverted
and are connected to the main arch by suitable bracing.
:
The Invention relates secondly to a novel method of relieving the
central piers of bridges from the unequal thrust of the arches caused by
the unequal loading of the same. This is effected by making the road-
way continuous against compressive strain from the abutment at one
end of the bridge to the abutment at the other end of the bridge so as

page_text: to bring the Horizo
abutments.
Ե arches ultimately on The Salu
The roadway may also be made continuous in such manner as to
resist tensional strains from pier to pier or abutment, and thus lessen
the compressive strains that would otherwise come against the abut-
ments.
Fig. 1 is a side view of a bridge with the roadway beneath the arch;
Fig. 2 is a similar view of a deck bridge; Fig. 3 is a top view; Fig. 4
is an end view; Fig. 5 is a side view of one end of the arch on an
enlarged scale; Fig. 6 is a top view of one side of same.
Fig. 7 is a side view of three arches illustrating the second part of
the Invention; Fig. 8 is a side view enlarged of one end of the arch;
Fig. 9 is a horizontal section of same looking downward; Fig. 10 is a
vertical longitudinal section of part of same.
Fig. 11 shews a means of bracing the arches at the ends in a through
bridge where the transverse or wind bracing is absent to allow head room
for the roadway. Similar letters of reference refer to the same parts in
all the Figures.
A is an upright arch connected to the abutments by hinged joints
B, B, and having a hinged joint C at its crown. D, D, are inverted
counter arches with their inner ends connected firmly to the main arch
at or near the joint C, and their lower or outer ends firmly fastened to
the main arch near the abutments or to the abutments at B, B. These
counter arches and the main arch are securely braced together by a
vertical brace system E, E, to hold them in their proper relative positions,
and this bracing must be sufficiently strong to transmit from the main
arch to the counter arches such portion of the weight of the load as
may be found by proper calculation necessary for the counter arches to
bear. The arch A and counter arches D, D, constitute one rib of the
bridge formed as will be seen by two independent half ribs joined
together at the centre by the joint C and supported at their outer ends
by the abutments. There should be in one span of the bridge two or
more of these ribs according to the strength and width required.
-
When a partial load is on one of the half ribs the counter arch of that
half rib is strained by tension as the weight is transmitted to it by the
vertical bracing between the counter arch and main arch on that side.

page_text: The unloaded half arch has at this time its counter arch under com-
pression, and forms with the main arch on that side an inclined strut,
supporting the central end of the loaded half, transmitting the pressure
of that end directly to the abutment against which the unloaded one
rests. The unloaded counter arch by its compressive strength and
vertical attachment to the unloaded half of the main arch prevents that
part of the main arch from rising up and losing its proper curvature.
The counter arches are under no strain whatever when the entire span is
equally loaded throughout, or when it is entirely unloaded, if the main
arch be of parabolic form. The counter arches merely truss the arch
against unequal loading, and their greatest strain in an arch of one-
eighth versed sine (the arch and counter arch being segments of circles
of the same radius) will be when the load extends over five-eighths of
the span.
The roadway F does not assist in any manner in the support of the
arches (unless constructed in a manner herein-after described), but is
connected to the arches only by vertical suspension rods G, G, as in
Fig. 1, or by struts G, G, as in Fig. 2, and by slip joints. Transverse
beams H may sustain the abutment ends of the roadway F, and if the
longitudinal members of the roadway are made of metal it must be
arranged to slide freely on these beams or other supports, as its length
is increased or diminished by change of temperature, which is simply a
modification of the slip joint above suggested.
When arranged as a deck bridge, as in Fig. 2, the roadway should be
directly attached to the arch near its crown so as to insure equal exten-
sions and contractions at both ends of the arch. I is a section of the
roadway inserted over the piers and between the main parts F of the
roadway (over the spans), the parts I being connected to those F by a
slotted or slip joint as at H. If the roadway is placed above and secured
near the central joint C its expansion and contraction will be easily
accommodated by the slight alteration in the vertical position of the .
struts G, G, as it will expand and contract in each direction from that
joint, and this will be accommodated by the sliding of the end on the
abutment.
If the roadway be suspended below, the suspension rods will adjust
themselves readily to the alterations in the length of the roadway,
excepting at each end of the span where they may be too short and

page_text: where the movements caused by change of temperature will be most.
excessive. At these points the suspenders should be arranged in stirrup
form, or the beam H may be used to allow the roadway to slide back
and forth. Although this movement will in an iron framed roadway
even in long spans be but a few inches it is important to accommodate
it in the way suggested, or by slip joint, or in the manner that trusses
are allowed to move longitudinally on the tops of bridge piers so as to
avoid the horizontal force that would otherwise exert itself to overturn
the piers or abutments, and which force if not thus accommodated
would require the piers and abutments to be so much stronger. If the
longitudinal parts of the roadway are made of timber these provisions
for expansion will be needless, as its alteration by temperature will be
so slight.
The roadway should be provided with wind bracings, and wind
bracings may likewise sustain the counter arches in position. Any
method of wind bracing is applicable to my system. When the road-
way is suspended of course a portion of the wind bracing between the
arches must be omitted at each end of the span for head room unless
the road be suspended some distance below. The widening of the ribs
at the abutments will allow the introduction of inside stays from the
abutments to the points of the upright ribs of the arch where the wind
bracing commences. This is shewn at L in Figures 3, 4, and 6; or the
ends of the arches where the wind bracing is omitted may be supported
by vertical posts or members strongly secured and braced to the floor
beams O, as shewn in Fig. 11.
In bridges where the span is so short that it is not desirable to have
the arches rise high enough to introduce wind bracing between them
and above the traffic the arches may be supported against lateral flexure
in this manner throughout the entire span.
With the roadway above (see Fig. 2) the stays L would be unnecessary, a
as the wind bracing between the ribs could then be continuous from end
to end. The object of these stays or vertical posts is to preserve the
arches in their proper planes where the necessity for head room for the
suspended roadway makes it necessary to omit the wind bracing between
the arches at the ends of the span.
The appearance of the span in Fig. 1, very much resembles the bow
string girder, but it is essentially different with the arrangement of

page_text: roadway, as described, as the thrust of the arch has no chord to resist
it but is taken solely on the abutments. The roadway F gives the
appearance of a chord and causes this resemblance. This method of
trussing the arch with the counter arches is however applicable to the
bow string girder, and will be found much more economic than any
other method of stiffening that form of girder.
The counter arches required in a railway span of five hundred feet to
carry two thousand five hundred pounds per linear foot are found by
careful investigation to need less than two-elevenths of the section of the
supporting arches. The weight of the arches and counter arches of this
system would be to the arches and cords of the bow string girder of
equal versed sine and strength, as thirteen to twenty-two, while the
vertical bracing would be considerably less than now used in the bow
string girder. The value of this feature of the Invention is shewn by
this comparison, the estimate having been carefully made for steel
arches with one-eighth versed sine, the wind trussing, and vertical
bracing being of iron; twenty thousand pounds per square inch being
the maximum strain allowed on the steel, and ten thousand pounds on
the iron. These counter arches constitute the simplest and cheapest
system yet devised for trussing or stiffening the arches of bridges. I
would recommend that the counter arches be of similar curvature to
the main arch. By lessening the radius of the counter arch (i. e.
increasing its versed sine) the strains in it will be reduced but the
lengths of the vertical bracing will be increased.
The sections or
voussoirs of the arch and counter arches should be straight between the
joints to which the bracing is attached to prevent flexure in them.
The second part of my Invention relates to a novel method of
relieving the piers supporting a series of arched spans from the
horizontal component of the thrust of said arches.
Suppose two spans constitute a bridge, and the above abutments
alone are constructed of sufficient strength to resist the thrust of the
arches with their loads, if the loads be equal and the arches are of the
same form and weight the thrust of one span against the central pier
will be balanced by the thrust of the other, and a pier or column simply
calculated to sustain the vertical pressure, as in ordinary trusses,
would be sufficient to insure stability. But if the load be removed
from one span the pier will be overturned by the thrust of the loaded

page_text: one. To prevent this overthrow of the piers, thus designed, by such
horizontal force, without the expense of increasing the size and weight
of the piers, I propose forming the chords of the wind trussing of the
roadway, and such other longitudinal members of the roadway as may
be necessary, of some non-expansible material (wood for instance), and
so abut these chords and lengitudinal members against the abutments
and piers, in or about the line of the springing of the arches, as to
cause the chords and members aforesaid in the unloaded arches to resist
by their compressive strength the horizontal force resulting from the
loading of any arch in the system. These distance picces or chords in
any one arch will not be in compression at the time the load is borne
by that particular arch, except when initial compression is produced in
them, as hereinafter stated, but if they were firmly secured to the piers
or pier and abutments supporting the arch, so as to resist tension, and
were constructed thoughout their length so as to resist tension; it will
be seen at once that the compressive strain thrown on the chords in the
other (unloaded) arches would be lessened by the amount of tension
born by the chords in the loaded arch.
The objection to combining timber with metal in the supporting
members of a truss does not apply in this method. In the truss one chord
(usually the top or compressive member) is sometimes made of timber,
but when this becomes decayed or injured it is scarcely possible to
replace it, save at the expense of constructing scaffolding, &c., to
sustain the entire truss during repair. In the proposed method any
chord or part of a chord may be readily removed without disturbing the
arches, piers, or other portion of the structure, for it will be seen that
if an equivalent weight were put on the floor beams of any one arch
its chords could be removed, and the stability of the arch would not be.
at all affected so long as the chords remained intact in the other spans
of the series.
It is only when the spans are unequally loaded that any strain at all
is on the proposed distance pieces or chords (except as hereinafter
stated), whereas in all forms of trusses whatever the chords are
constantly under strain, and hence repairs in them are almost impossible,
except at great inconvenience and expense.
Fig. 7 is a side view of a series of three spans arranged with the
proposed chords or distance pieces.

page_text: Fig. 8 is a side view of an end of one of these arches (on an enlarged
scale) shewing part of the counter arch, skew backs, and distance
pieces, secured by bolts to a socket in the skew back or bridge seat
resting on the top of the pier.
Fig. 9 is a top view of half the width of such system at the end of
a span; N, N, in the last three Figures represent three chords or
distance pieces, which will likewise serve as chords for the wind
trussing; 0, 0, Fig. 9, are transverse floor beams, and with the
diagonals P, P, and the chords N, N, constitute the system of wind
bracing; Qis a strong flat plate supporting the skew backs and
connecting the columns R, which constitute the piers supporting the
ends of the two arches; S, S, represent the skew backs; and T, T, the iron
screw straps joining the wooden chords to the brackets; U, U, are the
skew backs; V, V, represent lugs or brackets on the plate Q, to which
are to be secured the stays L, L, shewn in Figs. 3, 4, 5, or 11, to secure
the lower part of the arch against lateral movement where the wind.
bracing of the arch is omitted; W is a screw, having a nut X bearing
against the outer side of the bracket U, and acting compressively
against the end of the distance piece N for a purpose hereafter
described.
When an arch is loaded the distance pieces in the other arches will be
compressed, and consequently slightly shortened; this will have the
effect of slightly changing the positions of the tops of the piers, and if
this change be so great as to endanger the stability of the piers the
longitudinal movement of the bases of the arches may be accommodated
by arranging the skew backs and plate to slide on the tops of the piers,
after the manner of ordinary trusses, in which case the distance pieces
would abut against the skew backs (or screws W). Where several arches
constitute a series of spans and the load be on one span, the extent
of shortening in all of the chords of the unloaded spans from the hori-
zontal force of the load may cause the bases of the loaded arch to move
so far apart as to cause objectionable deflection in that arch. To
prevent this stronger abutments are provided, and adjusting screws W
are fixed at the skew backs of each arch to act against the distance
pieces in such manner as to produce a compressive strain throughout
the entire line of chords, from abutment to abutment, when the bridge
is unloaded. This initial compressive strain may be produced to such
an extent (by calculation) as to be just sufficient to relieve the chords

page_text: of an arch entirely of compressive strain when bearing the maximum
load, and yet not produce tension in it. In this case the deflection of
that arch will be limited by the compression in the arch itself due to the
load, and by the separation of the arch bases to the extent of the initial
compression in its own chords or distance pieces. In a series, for
instance of five arches, of say, five hundred feet span, where the
maximum horizontal force produced by the load on one arch equals five
hundred tons, if an initial compressive strain of four hundred tons be
produced in the entire system of chords from abutment to abutment by
the screws when the bridge is unloaded, then this initial strain will
be taken out of the chords of an arch next the abutment so soon as it
bears its maximum load, while the compressive strain in the remaining
chords will be proportionately increased.
When all the arches are loaded the strain on the abutments will be
five hundred tons plus four hundred tons plus the horizontal force of the
unloaded arches, say three hundred tons, making a total of one thousand
two hundred tons. This system is applicable to all of the ordinary
forms of truss bridges also, and by it the usual iron chords or tension
members of a series of trusses may be dispensed with and wooden
compression members or chords substituted, thus effecting an important
saving in cost.
It must be borne in mind that as each arch in an uniform system
balances the thrust of its neighbor the horizontal force against the
abutments remains the same whether there be one arch or any greater
number of arches in the same series. The same remark applies to 2
trusses also.
Owing to the expense and difficulty of joining a long series of timbers
in such manner as to bear the tensile strain throughout the length of
the series I prefer the method proposed of increasing the strength of the
abutments, and producing by screws (or their equivalent), as described, a
an initial compression strain, and thus avoiding tensile strains in these
chords. It may however be deemed desirable to have provision in them
for a small degree of tension, as in case of tornadoes where they act as
chords to the system of wind or horizontal bracing between them, and to
this end the timbers are joined to the skew backs by bolts and nuts, as 3
shewn in Figures 3 and 4, to resist tensile strains. Where these
fastenings are necessary the timbers forming the chords must be secured

page_text: also throughout the length of the chords to each other by splicing or
breaking joints, or other usual means for similar purposes.
Having now described the nature of the said Invention for "Improve-
ments in Bridges," as communicated to me by my foreign correspondent,
and having 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,—
First. The mode, herein described, of trussing or stiffening the upright
arches of a bridge by securing to each arch of the bridge two inverted
counter arches of half the span, maintained in position by suitable
vertical bracing between them and the main arch, and the counter
arches being fastened to the main arch at the centre and at the
abutments, as herein set forth.
Second. The mode, herein described, of relieving the central piers of
bridges from the unequal thrust of the arches (or equivalent members of
truss bridges) caused by moving loads, by making the roadway or longi-
tudinal members supporting the same continuous against compressive
strains from the abutment at one end of the bridge to the abutment at
the other end of the bridge, as and for the purpose set forth.
Third. In combination with the chords or distance pieces N, N, I
claim the compressive and tensional screws W and G, as and for the
purpose herein set forth.
In witness whereof, I, the said William Edward Newton, have here-
unto set my hand and seal, the Twelfth day of March, in
the year of our Lord One thousand eight hundred and seventy.