IMPROVEMENTS IN BEAMS AND GIRDERS
Year: 1859

page_text: LETTERS PATENT to William Henry Barlow, of Great George Street,
Westminster, for the Invention of "IMPROVEMENTS IN BEAMS AND
GIRDERS."
PROVISIONAL SPECIFICATION left by the said William Henry Barlow
at the Office of the Commissioners of Patents, with his Petition, on
the 11th April 1859.
I, WILLIAM HENRY BARLOW, of Great George Street, Westminster, do
hereby declare the nature of the Invention of "IMPROVEMENTS IN BEAMS
AND GIRDERS," to be as follows:-
This Invention has for its object improvements in the construction of beams
and girders, and is applicable to beams and girders which are furnished with
one or more intermediate supports in addition to the two terminal bearings.
It will be seen that an intermediate support applied to a beam may be
regarded as pressing upwards against the under side of the beam, and this
pressure of the support gives to the beam an upward flexure, that is to say, it
renders it convex on its upper surface, and concave on its under surface;
near the centre of each span of the beam the flexure is downwards, being
produced by the weight of the beam itself, and of the load upon it. Between
the centre of each span and the intermediate support, there is a point where
there is no flexure, and at this point the strain is less than at any other point

page_text: in the length of the beam. The upward pressure over the piers or
intermediate supports acts at a point, or nearly so, while the downward
pressure, occasioned by the weight and load, acts over the whole extent of the
beam, on which such weight and load is distributed; the consequence is,
that when a continuous beam is made of equal depth and section through-
out, and is loaded uniformly all over, the curvature upwards over the point of
support is sharper, that is to say, it is of less radius than the curvature
downwards in the centre of the span, and the breaking points of such a beam,
so loaded, would be at the places over the intermediate supports. If by any
means this point is shifted nearer to the centre of the span, the strength of the
beam is increased. In the construction of continuous beams or girders of
wrought iron, such girders have in some instances been made with an
increased section of metal in the flanges, at the parts over or near the piers,
but retaining the same depth; and in this manner a minor degree of
advantage is obtained, as regards the economical distribution of metal in the
flanges. Now, according to my Invention, in constructing beams or girders I
increase the depth of the beam or girder over and near the piers or
intermediate points of support, by which means I not only obtain greater
strength over the piers or intermediate points of support with the same
quantity of material in the flanges, but the radius of curvature of the upward
flexure is rendered greater, that is to say, the curve is flatter, and the points
of contrary flexure are thereby moved nearer to the centre of the span, so that
the sectional area of metal in the flanges, throughout the centre portion of the
beam, between the points of contrary flexure, may be considerably reduced,
without diminishing the strength of the beam, when compared with a beam of
equal section, or of equal depth throughout, as heretofore constructed. And it
will be seen in large girders, when the dead weight of the centre portion of
the beam is thus reduced, it also relieves in a proportionate degree the strain
over the intermediate pier, so that a great economy of material results from
this mode of construction. In constructing beams or girders upon this
principle, I continually diminish the depth from the maximum depth, over the
intermediate pier or support, to a point at or near the mean position of the
point of contrary flexure, which will usually be about halfway between the
intermediate pier or support and the centre of the span. And from this point
I continue the depth of the beam, equal, or nearly equal, through all the
centre portion of such beam. I also make the sectional area of the flanges at
and near the piers or intermediate supports, and also at and near the centre
of the span, proportional, or as nearly so as may be convenient to the
maximum strain, which would arise in such parts from the weight of

page_text: the structure itself, as well as from the insistent load, or any moving load
which it may be intended to carry; but to those parts which are at or near
the points of contrary flexure, I give a sectional area to the flanges greater
than is required to resist the strains to which such parts are subjected, for the
purpose of obtaining greater stiffness and less deflexion when the spans are
unequally loaded. When the continuous beam or girder is of considerable
length, I make a joint or joints in it at one or more of the points of contrary
flexure, to permit of the expansion and contraction of the beam or girder.
In constructing beams or girders of cast iron, as this material differs from
wrought iron, it being capable of sustaining a much greater compressive force
than tensile strain, it is usual to make the bottom flange of considerably
greater area than the top flange. In constructing continuous beams or girders
of this material, the same system has hitherto been followed; now, according
to my Invention, at the points over and near the piers or supports, I make
the top flange of greater area than the bottom flange, to meet the change in
the direction of the strain. I also at these points give to the beam a greater
area of section than it has at other parts of its length, and also a greater depth.
If the continuous beam or girder is of such a length as to have to be cast in
more than one piece, I arrange the joints to fall at or near the points
of contrary flexure, the length of girder necessary to pass from one point of
contrary flexure, over a pier or support, to the next point of contrary flexure,
being always cast in one piece.
Another part of my Invention relates to beams or girders, whether
continuous or detached; and when continuous, whether the depth over
the pier is encreased, or whether the depth is equal throughout; and it
consists in the employment of a stronger material, such as puddled steel,
to form the whole of the centre portion of such girders, or the principal parts
thereof, for a length equal to from one-third to one-half of the span. By
these means I obtain the requisite strength in this part with a much
less weight of material. The reduction in the dead weight of the centre
portion so obtained, enables me by this arrangement to reduce the sectional
area and weight of wrought iron in all the other parts of such beans
or girders.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said William Henry Barlow in the Great Seal Patent Office
on the 11th October 1859.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, WILLIAM
HENRY BARLOW, of Great George Street, Westminster, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Eleventh day of April, in the year of our Lord
One thousand eight hundred and fifty-nine, in the twenty-second year of
Her reign, did, for Herself, Her heirs and successors, give and grant unto
me, the said William Henry Barlow, Her special licence that I, the
said William Henry Barlow, my executors, administrators, and assigns,
or such others as I, the said William Henry Barlow, 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 BEAMS AND GIRDERS,"
upon the condition (amongst others) that I, the said William Henry Barlow,
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 Henry Barlow, 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 thereof, that is to say :-
.This Invention has for its object improvements in the construction of beams
and girders, and is applicable to beams and girders which are furnished with
one or more intermediate supports in addition to the two terminal bearings.
It will be seen that an intermediate support, applied to a beam, may be regarded
as pressing upwards against the under side of the beam, and this pressure of
the support gives to the beam an upward flexure, that is to say, it renders it
convex on its upper surface and concave on its under surface; near the centre
of each span of the beam the flexure is downwards, being produced by the
weight of the beam itself and of the load upon it. Between the centre of
each span and the intermediate support there is a point where there is no

page_text: flexure, and at this point the strain is less than at any other point in the
length of the beam. The upward pressure over the pier or intermediate
supports acts at a point or nearly so, while the downward pressure occasioned
by the weight and load acts over the whole extent of the beam on which such
weight and load is distributed; the consequence is, that when a continuous
beam is made of equal depth and section throughout, and is loaded uniformly
all over, the curvature upwards over the point of support is sharper, that is to
say, it is of less radius than the curvature downwards in the centre of the
span, and the breaking points of such a beam, so loaded, would be at the
places over the intermediate supports.
In the construction of continuous beams or girders of wrought iron, such
girders have in some instances been made with an increased section of metal
in the flanges at the parts over or near the piers, but retaining the same
depth, and in this manner a minor degree of advantage is obtained as regards
the economical distribution of metal in the flanges. Now, according to my
Invention, in constructing beams or girders, I increase the depth of the beam
or girder over or near the piers or intermediate points of support, by which
means I not only obtain greater strength over the piers or intermediate points
of support with the same quantity of material in the flanges, but the radius of
curvature of the upward flexure is rendered greater, that is to say, the curve
is flatter, and the points of contrary flexure are thereby moved nearer to the
centre of the span, so that the sectional area of metal in the flanges through-
out the centre portion of the beam, between the points of contrary flexure, may
be considerably reduced without diminishing the strength of the beam when
compared with a beam of equal section or of equal depth throughout, as here-
tofore constructed. And it will be seen that in large girders, when the dead
weight of the centre portion of the beam is thus reduced, it also relieves in a
proportionate degree the strain over the intermediate pier, so that a great
economy of material results from this mode of construction. In constructing
beams or girders upon this principle, I continually diminish the depth from
the maximum depth over the intermediate pier or support to a point at or
near the mean position of the point of contrary flexure, which will usually be
about half way between the intermediate pier or support and the centre of the
span. And from this point I continue the depth of the beam equal or nearly
equal throughout all the centre portion of such beam; I also make the.
sectional area of the flanges at and near the piers or intermediate supports,
and also at and near the centre of the span proportional, or as nearly so as
may be convenient to the maximum strain which would arise in such parts
from the weight of the structure itself as well as from the insistent load, or.

page_text: any moving load which it may be intended to carry. But to those parts which
are at or near the points of contrary flexure, I give a sectional area to the
flanges greater than is required to resist the strains to which such parts are
subjected for the purpose of obtaining greater stiffness and less deflection when
the spans are unequally loaded.
The Diagram A shows a girder with lattice or open work sides, constructed
according to my Invention, and Diagram B shows a girder with plated sides.
suitable for supporting a roadway or platform on its upper flanges; for con-
venience of doing this, the increased depth over the girder is given by lowering
the bottom flange in place of raising the upper flange. In constructing
girders upon this principle, I prefer the following proportions, namely,-
The depth of the girder over the pier to be 1 times the depth at the
centre. The centre depth to remain equal between the points A, A, being a
distance equal to one half of the clear span. From the points A, A, to the
piers the depth increases in an arithmetical ratio to the maximum depth at the
pier. The sectional area of the flanges at the pier to be 1 times the sectional
area at the centre. And the sectional area at the points A, A, to be, of the
sectional area at the centre. The depth of the girder at the centre to be
about 1th of the clear span, but may vary from th tooth. To girders of
these proportions the following rules for finding the actual section to be given
to the different parts apply. In constructing a continuous girder upon this
principle it is first necessary to ascertain the approximate weight of the
intermediate span, and this for wrought iron may be done as follows:-
Multiply the intended maximum load in tons per foot (both dead load and
moving load) by the cube of the span in feet, and use this as a numerator.
Then if the girder is to be made with lattice or open work sides, multiply
the depth in feet at the centre into the intended maximum strain per inch upon
the metal in tons, and by the number 3600, and from the product deduct the
square of the span in feet, use this as a denominater. Divide the numerator
by it, and the quotient will be the approximate weight of the girder in tons.
If the girder is made with plate sides, multiply the depth of the girder in feet
at the centre by 2820 times the intended maximum strain upon the metal
per inch in tons, and deduct from the product the square of the span in
feet. Use this as a denominater and divide the numerator by it, and the
result will be the approximate weight of the girder in tons. The weights
thus found are for the clear distance between the supports of one of the
intermediate spans. It is next necessary to find the strain on one of the
flanges at the centre of the girder; to do this, add together the weight of
the girler, the dead load, and the maximum moving load, which can come

page_text: on one span in tons.
Or multiply the maximum load per foot in tons
(both dead and moving load) by the length of one intermediate span in
feet for the gross maximum load and add it to the weight of the girder.
Then to find the section to be given to the flanges at the centre, multiply
the total weight in tons thus obtained by the span in feet, and divide the
product by twenty times the depth of the girder at the centre in feet, the
result will be the strain at the centre in tons. The strain at the centre
divided by the intended strain per tons per inch will give the net section at
the centre. One and a half times this quantity will be the sectional area at
the piers, and of the centre section will be the section at A and A.
The sectional area of the intermediate parts will be determined by the usual
rules, observing, however, that no part of the flanges is to be made less
than the section of the centre. The above rules applied to three
or more contiguous spans, when the terminal spans are of the centre
span, or intermediate span, or thereabouts. If the terminal spans are
less than, or more than 1 of the intermediate spans, or if the inter-
mediate spans are unequal in magnitude, it is necessary specially to calculate
the positions of the points of contrary flexure under the extreme variations
of the moving load, and proportion the parts accordingly. The sides of
the girder whether of latticework plates, or the construction known as
Warren's sides, will be the same as for a detached girder of the same
weight, span, and load. When the continuous beam or girder is of considerable
length I make a joint or joints in it at one or more of the points of contrary
flexure to admit of the expansion and contraction of the beam or girder, the
two ends of portions of a lattice beam jointed in this manner are shewn in
elevation at Figure 1, in plan at Figure 2, and and an end view of one of them
at Figure 3. It will be seen that each of the portions of the girder is furnished
with two sets a, a, a', a' and suspension links b, b, b', 6', pass from the
lugs of one portion of the girder to the lugs of the other portion. Figures 4
and 5, show a part of one of the portions of the girder on an enlarged scale in
side and end view respectively. In constructing beams or girders of cast
iron, as this material differs from wrought iron in its being capable of sustaining
a much greater compressive force than tensile strain, it is usual to make the
bottom flange of considerably greater area than the top flange. In constructing
continuous beams or girders of this material the same system has hitherto
been followed; now according to my Invention at the points over and near
the piers or supports I make the top flange of greater area than the bottom:
flange to meet the change in the direction of the strain, I also at these points,
give to the beam a greater area of section than it has at other parts of its

page_text: length, and also a greater depth. If the continuous beam or girder is of such
a length as to have to be cast in more than one piece I arrange the joints to
fall at or near the points of contrary flexure; the length of girder necessary
to pass from one point of contrary flexure over a pier or support to the next
point of contrary flexure being always cast in one piece.
Figure 6 is a side view, and Figure 7 a plan of a continuous beam of cast
iron, jointed at intervals, and constructed according to my Invention; Figure 8
is a section of the same, taken at the line A, A, Figure 6; Figure 9 is also
a scction taken at B, B, Figure 6; Figure 10 is an end view of one of the
portions of the girder, and Figure 11 is a side view of the joint and the parts
near it, shown on an enlarged scale.
Cast iron should only be employed in small spans where the weight of the
girder is very small as compared with the load it has to bear, and the section
of metal to be given to the parts of the girder in any particular case will be
determined as follows:-Ascertain by the ordinary rules the sectional area
of the bottom and top flanges required for a detached beam of the ordinary
construction, and of the same depth, space, and level, make the sectional area of
the flanges at the centre one-half of those of the detached beam, and make the
sectional area of the flanges at the piers of the same, placing the large flange
at the pier uppermost, as shewn in the Drawings. The flanges are to be
diminished toward the points A, A, in the manner shewn.
Another part of my Invention relates to beams or girders, whether con-
tinuous or detached, and when continuous, whether the depth over the pier is
increased or whether the depth is equal throughout, and it consists in the
employment of a stronger material such as puddled steel to form the whole of
the centre portion of such girders, or the principal parts thereof for a length
equal to from one-third to one-half of the span; by these means I obtain the
requisite strength in this part with a much less weight of material, the reduction
dead weight, of the centre portion so obtained enables me, by this arrange-
ment, to reduce the sectional area and weight of wrought iron in all the other
parts of such beam or girder.
When puddled or Bessemer's steel is used in conjunction with wrought iron in
a continuous girder of my form, I apply it according to the following rule :-The
steel is to be used in the upper and lower flanges of the centre portion of the
girder, but in consequence of the cost of the material only in those cases
where the spans are so large that the weight of the girder exceeds the weight
of the load, and it becomes of importance to reduce the weight of the girder by
every practicable means.
Puddled steel and Bessemer's steel has been found by experiment capable

page_text: of bearing double the strain of wrought iron, and when so applied the rule for
obtaining the sectional areas of steel at the centre and of iron at the piers will
be as follows:-Multiply the maximum load in tons per foot lineal (both the
dead load and moving weight) by the cube of six-tenths of the span in feet, and
use this as a numerator. Multiply 900 times the depth of the girder in feet
at the centre by the maximum strain in tons per inch intended to be placed on
the steel, and from this result deduct the square of six-tenths of the span in
feet, and use the remainder for a denominator. Divide the numerator by the
denominator, and use the result as follows:-Multiply the maximum load per
foot run by six-tenths of the span in feet, and add it to the number found as
above directed. Divide the sum by eight times the depth of the girder at the
centre in feet, the result will be the maximum strain upon the upper or lower
flanges at the centre. Divide this strain by the maximum strain per ton per
inch intended to be placed on the steel, or by twice the strain per ton per inch
intended to be placed on the iron, and the result will be the sectional area
required at the centre in inches. Three times the sectional area of steel
at the centre will be the sectional area of iron required over the piers, which
will produce the ratio of 1 to 1 in the strengths as herein-before described
for wrought iron, it being assumed that the maximum strain to be brought on
the steel is twice that to be brought upon the iron.
It is recommended, however, that in any large structure the rules here given
should be used as approximations, and that the positions of the points of
contrary flexure, and the strains on the several parts should be calculated by
the known rules for that purpose as applied to girders of this form.
In applying steel in detached girders I introduce it into the flanges either at
the centre portion of the girder only or throughout. In this manner also
increased strength may be given to continuous girders of the ordinary
construction.
In witness whereof, I, the said William Henry Barlow, have hereunto
set my hand and seal, this 11th day of October, in the year of our
Lord One thousand eight hundred and fifty-nine.
WILLIAM HENRY BARLOW. (L.S.)"