AN IMPROVED BRACED GIRDER
Year: 1884

page_text: I WILLIAM CAMPBELL of 30 Lefroy Street in the City and County of Newcastle
on Tyne Civil Engineer do hereby declare the nature of my invention for "AN
IMPROVED BRACED GIRDER" to be as follows:-
To perform the Bracing in a Girder so as to obtain nearly twice the usual
strength and stiffness in the Girder from the usual quantity of material as is
obtained in any other manner of bracing.
There are a top longitudinal bar or flange and a bottom longitudinal bar or flange
with an intermediate longitudinal bar or stringer at about half the depth in the
girder; each of these three bars extending the whole length of the Girder. Two
zig-zag rows of diagonal bars with vertical bars connect the flanges with the
stringer to form the girder. One end of each diagonal in the upper zig-zag row is
attached to the top flange and one end of each diagonal in the lower zig-zag row is
attached to the bottom flange, and the other ends of the diagonals in each row
are attached to the intermediate stringer at alternato points along its length.
There are also vertical bars connecting the flanges with the stringer at the same
points as the diagonals.
I strengthen the end verticals and haunch diagonals as pillars to resist the
straining force of vertical shearing at the piers in the usual manner.
The flanges resist the two longitudinal strains of extension and compression
induced by bending from the weight of the girder and its load.
Having discovered by calculation and experiment that the extra strength known
to exist in a solid beam beyond the calculated strength due to the fibres is resistanco
to the longitudinal force of detrusion at the neutral axis of the beam I have
invented this manner of obtaining additional strength by resisting horizontal
detrusion as a third longitudinal force.
This force comes in contrary directions alternately from the diagonals and is
absorbed in the intermediate stringer instead of being transmitted directly to the
opposite flange as is the case when the diagonal continues in a direct line from
flange to flange.
When the girder is strained the turning points of the diagonals are in the inter-
mediate stringer and so the flanges are not fulcrums to one another.
Therefore in calculating the strength of this neutral axis girder I can take the
strength of both the top flange and the bottom flange as giving their united
strength in the girder and not have to take the strength of only one of the flanges
as has to be done in calculating the strength of all other girders.

page_text: Hence by performing this invention I get about twice the usual strength in the
girder from about the usual quantity of material in the construction of a braced
girder.
This girder is twice as stiff as any other girder of equal weight.
There being two diagonals in the depth of the girder double work is got from
them as they do not extend across one another and are not in a direct line with
one another.
The advantage of double the usual strength and stiffness is obtained in this
invention by terminating the diagonal bars at alternate points upon an intermediate
longitudinal stringer bar.
The vertical bars may be extended the whole depth of the girder if required to
steady the bays of the flanges or carry the cross girders for the roadway of a
bridge.
I have drawn the girder straight but the top flange and bottom flange may be
curved towards each other, the intermediate stringer remaining straight or the
whole girder may be arched up to form a roof.
The depth is shewn at one eighth of the length but these may be of any usual
ratio. The diagonals are set at 45° as the best angle.

page_text: I WILLIAM CAMPBELL of 30 Lefroy Street Newcastle upon Tyne in the County
of Northumberland Civil Engineer, do hereby declare the nature of my invention
for AN IMPROVED BRACED GIRDER, and in what manner the same is to be
performed, to be particularly described and ascertained in and by the following
statement:-
This improved braced girder for bridges roofs and like purposes is formed with
longitudinal vertical and diagonal bars which consist of bar iron or of plates and
angle iron riveted together all these bara being fixed and joined to form a braced
girder in the usual manner of riveted wrought iron bridge work according to the
following arrangement of these parts and as shown in the drawing accompanying
my prov spec.
A longitudinal top bar or boom or flange forming the top of the girder throughout
the whole length of the girder, and a longitudinal flungo forming the bottom of the
girder, each extending throughout the whole length of the girder.
These top and bottom flanges are braced together by the following bars to form
a girder.
An intermediate longitudinal stringer bar which extends in a direct line
throughout the whole length of the girder and by straight vertical bars and by
straight diagonal bars forming the web of the girder with a double row of triangular
spaces between the top and bottom flanges.
Fixed in each end of the girder are bars forming pillars in the usual manner
where the girder rests upon piers.
The intermediate bar is fixed at about half the depth of the girder.
Each vertical bar and each diagonal bar reaches through about half the depth of
the girder and they connect the top and bottom bars with the intermediate bar
upon which they all terminate at alternate points.
One end of each vertical bar is attached to the intermediate bar beside the ends
of two diagonal bars at regular intervals apart equal to about half the depth of
the girder. They reach alternately one to the top bar and the next to the bottom
bar and are attached to thein at equal intervals apart which are twice as long as
the intervals upon the intermediate bar being equal to about the whole depth of
the girder.
The diagonals are set by preference at an inclination of 45 degrees with the
intermediate bar.
One end of each diagonal bar is fixed to the intermediato bar, the ends of two
diagonal bars coming near together close to where each vertical bar is fixed the
two diagonal bars being inclined at contrary inclinations. Their other ends are
fixed to the top bar and to the bottom bar respectively two ends near together
close to where each vertical bar is fixed to these longitudinal bars symmetrically
throughout the whole length of the girder between its end pillars.
The points at which the diagonal bars and the vertical bars meet close to
each other & are attached respectively to the top bar and to the bottom bar
are at alternate distances along the girder and as the diagonal bars and the vertical
bars all terminate upon the intermediate bar and are attached to it at regular
intervals along the girder there are as many points of attachment of verticals and
diagonals upon the intermediate bar as there are together upon the top and bottom
bars, the points upon the intermediate bar coming alternately opposite the points
upon the top and bottom bars, thus bringing the diagonals attached to the top bar
immediately over the diagonals attached to the bottom bar symmetrically through
out the length of the girder, so that the whole length of one diagonal comes

page_text: immediately over the whole length of another diagonal and is parallel to it forming
two seperate diagonals in the depth of the girder, neither of which extends through
the whole depth of the girder, the diagonals attached to the top bar not coming in
a direct straight line with the diagonals attached to the bottom bar and not
extending across one another.
This arrangement of the intermediate longitudinal bár, the vertical bars and the
diagonal bars connecting the top longitudinal bar and the bottom longitudinal bar
completes the bracing of the girder
T
This is a new manner of performing the bracing and forming the web of the
girder, and all the bars fixed together in this manner forms the improved braced
girder: but each girder may be of a box form and may have two or more such
webs, side by side, between its top and bottom flanges the depth of the girder
being the same as for a single web.
The top bar and the bottom bar may each or either of them be formed as a flange
as a boom or as a trough.
The intermediate longitudinal or stringer bar may consist of two or more
longitudinal bars connected by vertical plates and angle irons. Additional bars
may be fixed at the points where the vertical bars are attached to the intermediate
longitudinal bar and be extended upwards as pillars to the top longitudinal bar, or
downwards as suspenders to the bottom longitudinal bar when the intervals or
bays are long as in long span girders.
This arrangement of bracing bars may be used horizontally between the longi-
tudinal girders of a bridge to stiffen it sideways and also to carry the roadway,
and it may be used as the internal bracing of a pillar or in a partition or other
framing or in the roofing of a railway station or other large roof.
A girder with the bracing arranged in the manner of this Invention can be
constructed of bars of timber fastened together with tree-nails an iron spikes and
for which it is peculiarly well suited because only half the usual strain comes upon
the end fastening at points of attachments of the diagonals, as the intermediate
stringer being in the neutral axis of the girder absorbs the re-action of the
diagonals and prevents it from being transmitted direct to the opposite flange the
stringer at same time relieving the flanges of part of the bending strain.
The intermediate stringer requires to be half the size of either flange and as it
is strained in extension only in every alternate interval of its length, timber
joinings can easily be made in the intervening intervals because they are in
compression.
Also the shortness of the diagonals is favourable to increased depth of girder
suitable for timber work when such is preferred to ironwork.
Thus in performing this "improved braced girder" I use in the web of the
girder diagonal bars, two ends together at contrary inclinations attached to the top
longitudinal bar, close beside the ends of vertical bars, also other diagonal bars
similarly attached to the bottom longitudinal bar and attached by their other ends
to the intermediate longitudinal bar, upon which they all terminate at alternate
points, close beside the other ends of the vertical bars; two diagonals in the
depth of the girder parallel to each other, without either diagonal by itself reaching
through the whole depth of the girder.
There are thus as many places upon the intermediate bar where the ends of two
diagonals meet as there are upon the top bar and upon the bottom bar summed
together, forming two zig-zag rows of diagonals cach row extending the whole
length of the girder without crossing one another.
Having now particularly described and ascertained the nature of my said
Invention and in what manner the same is to be performed I declare that what
I claim is
"
1. Attaching to an intermediate longitudinal bar which is fixed at about half the
depth of the girder and extends along the whole length of the girder, the ends of
diagonals in pairs in which one is inclined to the right and the other to the left at
samular distances along the minden

page_text: 2. Having the diagonals which are attached by one end in pairs to the top har,
attached by their other ends in pairs to the intermediate bar alternately with
similar pairs of diagonals, which have their other ends attached in pairs, at
intervening distances along the bottom bar.
3. Having two diagonals in the depth of the girder, one wholly above and
parallel to the other, each reaching through only about half the depth of the
girder.
4. Having two pairs of diagonals in the depth of the girder, at each vertical,
without crossing one another, and without any diagonal coming in a direct line
with any other diagonal.
5. Having all the diagonals terminating in pairs upon the intermediato bar,
and terminating in pairs alternately upon the top and upon the bottom bar
symmetrically along the girder.
6. Having the places of attachment of the ends of pairs of diagonals upon the
intermediate bar alternately opposite to the similar places upon the top and
bottom bars.
7. Having as many pairs of diagonals attached by their ends upon the inter-
mediate bar as upon both the top and bottom bars together.