Improvements in Concrete-and-iron Beams, Girders, Cantilevers, Railway-sleepers, and the like.
Year: 1894

page_text: Date of Application, 14th Aug., 1894-Accepted, 6th Oct., 1894
Improvements in Concrete-and-iron Beams, Girders, Cantilevers,
Railway-sleepers, and the like.
I, FREDERICK GEORGE EDWARDS, of 120 Leighton Road Kentish Town
London do hereby declare the nature of this invention and in what manner the
same is to be performed, to be particularly described and ascertained in and by the
following statement :-
This invention relates to improvements and developments of the concrete-and-
iron beams described in my previous Specifications of Letters Patent No. 2941
A.D. 1891 and No. 1415 A.D. 1892.
Fig. 1 shows a half-elevation and Fig. 2 a central section of a model of a new
form of concrete-and-iron girder 2" wide and 6" deep for a 4' 0" effective span
designed for a central load and tested by Messrs. Kirkaldy & Son. The model
had twenty " iron wires A in the underside at the central section four of which
immediately curved upwards at an angle of 45° on each side and the rest similarly
curved upwards in sets B of four at intervals of 6" leaving four horizontal wires to
reach to the ends. The ends of all the wires were corrugated and the concrete
pierced by seven circular openings C of 3" diameter. The model, composed of
equal parts of Portland cement and coke breeze, was made on the 19th April 1892
and tested on the 11th August 1894 when the load was applied at the bottom of
the central opening. The following is an abridgment of Messrs. Kirkaldy & Son's
report :-

page_text: The placing of a concentrated load at the bottom of the central opening was a
severe test which thoroughly established the principle of this class of concrete-
and-iron girder. Calling the load which produced a deflection of th inch, in
round nunibers, 3th of a ton and the ultimate breaking load 2 tons, the strength
that may be expected with similar larger girders can be readily calculated as it 5
increases as the square of the span. The following table compares girders for ten,
twenty, and forty feet span with the tested model :-
Fig. 3 shows a half-elevation of a similar concrete-and-iron girder for a 40' 0"
effective span 1' 8" wide and 5' 0" deep, but designed for a distributed load which
may be applied in the openings C or rest on the top of the girder as may be
convenient. One rod or bar only curves upwards at m, two at n, four at o, and
seven at p (the latter in two series) leaving six to pass to the end of the girder.
Such a girder, being ten times the dimensions of the model previously described, if
composed of exactly similar materials would require a uniformly distributed load of
500 tons to break it, while a distributed load of 133 tons (or 3½ tons per foot run)
would not produce a greater deflection than one inch.
The girder may be ornamented by smaller openings e connected by sunk
rhomboidal panels as shown, thereby forming the concrete struts 8.
One half the bars in each of the sets B may be arranged to cross the other half
diamond-wise; or the ends of one half may be separated from the ends of the other
half as indicated by the dotted lines in Fig. 3.
The curving upwards of the bars in sets B may take place at shorter or longer
intervals and the sets are inclined at a suitable angle with an easy curve to prevent
crushing of the concrete. It is evident that rivet or other heads or collars formed
on the bars may be substituted for the corrugations.
Fig. 4 shows an elevation of a concrete-and-iron girder with the bars curved
upwards in sets B at shorter intervals; and Fig. 5 shows an elevation of another
concrete-and-iron girder with the sets B placed at a sinall angle so that they all
reach to the end of the girder.
In all the drawings the bars are for convenience shown in full lines.
i
I have discovered that the stresses on the inclined portions of the bars are
exactly proportionate to the number of bars that can be spared from the underside
of the girder. Let the line ab (Fig. 6) represent graphically the difference
between the tensions on the horizontal bars at two adjacent points where they
curve upwards as at m and n (Fig. 3) which in other words is the direct force
producing shearing between those points. Draw a c parallel to the inclination of
the bars and b d parallel to a c. Draw the line b c bisecting the angle a b d. This
line represents the resultant of the pressure of the inner side of the curved bars

page_text: on the concrete and the tension in the rods must therefore be represented by the
line a c which is equal to a b.
Fig. 7 (Sheets 2 and 3) is an isometric projection of a concrete-and-iron
cantilever suitable for bridging large spans. In this case the bars A turn down-
wards in sets B and the building of a pair of cantilevers is commenced, as usual in
iron construction, at the central pier H and proceeded with simultaneously at each
side, the concrete being deposited in sections of suitable shape such as for instance
the section abcdef; and if the bars corresponding to each section are embedded
throughout their length at one operation each pair of cantilevers may be completed
in sections without detriment to their ultimate strength. The bars may be jointed
by any ordinary means to obtain sufficient length. Openings may be made
through the concrete similarly to those described for the girder in Fig. 3 and used
to receive the ends of transverse beams or girders if necessary. If the ends of the
cantilevers are required to receive a central girder K, some of the bars at those
ends must be arranged to pass under the bearing of the girder so as to obtain.
sufficient resistance to shearing. One half the bars in each of the sets B may be
arranged to cross the other half diamond-wise; or the ends of one half may be
separated from the ends of the other half as previously described with reference to
the girder (Fig. 3). The ends of the bars may be corrugated; and may also
project through one section of concrete as at g so as to key the adjacent section
afterwards deposited. The different sections of concrete may be deposited in a
suitably designed box supported from the cantilever by means of a movable staith,
the principal framework of which consists of two side trusses extending above and
below. The staith is fitted and arranged so that it can be moved forward when.
the section last deposited has sufficiently set and the box is released. If vertical
joints are made in the horizontal layers of concrete at the top of the cantilever,
these should break joint with each other; and likewise the joints of the steel bars
should not be all at one point.
In bridge cantilevers of large projection where their own weight becomes the
principal part of the load it will be economical to make them of uniform strength
by varying their depth; but as this increases the intensity of the shearing stresses
at the ends of the cantilever and consequently at the ends of the bars also thereby
reducing their hold on the concrete it is necessary to inquire to what extent the
depth of the cantilevers may be varied with safety.
The bending moments of a cantilever due to a uniformly distributed load may be
represented graphically by the parabola A B C (Fig. 8, Sheet 4) and compared
with the bending moments of half a girder having twice the span and similarly
loaded, which are represented by the parabola A D C. The corresponding shearing
stresses represented by the line G C for the cantilever and by the line E F for the
semi-girder show that in the latter case the maximum total shearing stresses are at
the ends of the bars, and in the former at the middle of their length which is much
more favourable for their hold on the concrete. This distribution of the shearing
stresses shows that there is a large margin for varying the depth of the cantilever
as compared with girders supported at the ends without reducing the hold of the
bars; also as the weight of the cantilever itself will then increase towards the
piers this will increase the bending moments and also the shearing stresses towards
the piers; while on the other hand as the cantilever is made to approach uniform
strength by varying the depth the actual tensile and compressive stresses approach
uniformity throughout and the shearing stresses on the surfaces of the bars tend
to concentrate at their ends. It is therefore evident that cantilevers of large
dimensions may be so designed that the intensity of the shearing stresses on the
surfaces of the bars as nearly as possible are uniform and the tensile stresses in
each set of bars consequently uniformly increasing in amount towards the piers as
may be represented graphically by the lines M N and ST (Fig. 9) which are
intended to represent the intensity of the stresses actually produced on and in one
set of bars and not the bending moments and shearing forces acting on the canti-
lever as in the preceding figure. The cantilever may be readily designed in this

page_text: manner as the intensity of the shearing stresses on the surfaces of the bars at any
given point varies directly as the intensity of the vertical shearing stresses on the
cantilever at the same point. The hold of the longest bars may be still further
increased by making the outer end of the cantilever nearly uniform in depth for a
considerable length, and also the hold of the shorter bars by their bending down-
wards in sets B (Fig. 7) as previously described. Furthermore the ends of all the
bars may be corrugated. The cantilevers may of course be varied somewhat in
width if necessary without affecting the hold of the rods. A study of the
distribution of the stresses by the aid of the diagram (Fig. 8) shows that the
cantilever is even better suited for concrete-and-iron construction than the beams
and girders previously described.
I prefer round steel bars or rods for embedding in the concrete but steel or
iron bars of square or other section may be used.
The construction of these girders and cantilevers is exceedingly economical as
one uniform section of steel only need be used throughout and the joints bends and
corrugations may be all of one pattern. The concrete also is deposited in large
• masses.
Concrete-and-iron railway sleepers may be lightened by making them of the
shape shown by Fig. 10 in plan but of a uniform thickness. The chairs are to be
secured by bolts; and the rods embedded in the same manner as described in my
Specification of Letters Patent No. 1415 A.D. 1892, except that they are equally
distributed throughout the mass of the concrete at the central neck P and also at
the ends they are concentrated in a layer at the bottom of the sleeper under the
rails at R as before.
:
Having now particularly described and ascertained the nature of my said inven-
tion and in what mauner the same is to be performed, I declare that what I
claim is
1. Concrete-and-iron beams girders and the like with the tension bars or rods
curved upwards in sets B as described with reference to Figs. 1, 2, 3, 4, and 5.
2. Concrete-and-iron semi-girders or cantilevers and the like with the tension
bars or rods curved downwards in sets B as described with reference to Fig. 7.
3. The improved concrete-and-iron (or the like) railway sleepers as described
with reference to Fig. 10.
Dated this 14th day of August 1894.