IMPROVEMENTS IN IRON BRIDGES
Year: 1864

page_text: LETTERS PATENT to Joseph Westwood, junior, of Tredegar House;
Bow, in the County of Middlesex, for the Invention of "IMPROVEMENTS
IN IRON BRIDGES."
Sealed the 16th June 1865, and dated the 21st December 1864.
PROVISIONAL SPECIFICATION left by the said Joseph Westwood at the
Office of the Commissioners of Patents, with his Petition, on the
21st December 1864.,
I, JOSEPH WESTWOOD, junior, of Tredegar House, Bow, in the County
of Middlesex, do hereby declare the nature of the said Invention for
IMPROVEMENTS IN IRON BRIDGES," to be as follows :-
These improvements are more particularly applicable to the lower hori-
zontal members or tension chains of the variety of iron bridge girders, for
which James Warren and Willoughby Theobald Monzani obtained Letters
Patent, dated August 15th, 1848, Number 12,242; but these improvements
are also applicable to the upper tables or horizontal compression members of
the same variety of bridge girders, and they may be applied, with a certain
degree of advantage, to both the upper and the lower flanges of certain other
varieties of girders.
It is well known that the requisite strength of the upper and lower hori-
zontal members or flanges of a bridge girder or truss increases progressively

page_text: from the ends towards the middle of their length. In Warren's girders the
requisite strength of the horizontal tension links, for example, increases in
each triangle from the ends to the centre or mid span.
Where the triangles
in a Warren girder are large, it is usual to provide the requisite strength
with as much exactness as is practicable in each triangle. Where the span
is short, it is usual, for convenience of construction, to employ tension links of
a length sufficient to span two or more triangles. In this case, as the links
have the same section throughout their whole length, the distribution of iron
is not exactly that due to the strain in the several triangles, and hence there
is a waste of material. Where, in larger triangles, the section of the links is
exactly that proper for the strain in each triangle, there is still a loss of
metal in the "overlaps " of one set of links in each triangle past and beyond the
ends of the links in the adjacent triangles. There is also in this case a
greater amount of drilling required in forming the holes for the pins which
connect the links together into the lower tension member of the girder than
where the same links extend over two or more triangles; and the pins for
connecting the links together are longer and consequently heavier where there
is a separate set of links for each triangle than where the links each cover two
or more triangles.
Now, my improvements in iron bridges, especially when applied to the
lower or tension members of Warren's girders, permit of the exact requisite
distribution of iron in the links of the triangles; and I am furthermore
enabled to save a considerable part of the iron now wasted in "overlaps " at the
connecting pins, and I obtain also the least permissible length and weight of
the connecting pins themselves; and furthermore, whereas the lower or
tension members of a Warren's girder, as commonly made, are flexible chains,
having free vertical movement upon their connecting pins, the lower member
of a like girder upon my improved construction would have a considerable
degree of vertical stiffness of itself, even when unconnected with the other
parts of the girder, and it could be erected, therefore, with less staging or
other temporary support.
The mode which I adopt for forming the lower or horizontal tension
member of, a Warren girder is as follows, the description proceeding from
either end towards the.middle of the length of the girder :--I take one or more
bars of a section, or collective section, proper for the lower tension link of the
end triangle, but of a length sufficient to span horizontally along two or more
triangles; along that portion of the length of this bar or these bars which corre-
sponds to the second triangle from the end of the girder I apply another bar.or
bars of such section that, together with the first bar or bars described, the second

page_text: bar or bars shall give the exact requisite strength for the lower tension
member or link of the second triangle. The second bar or series of bars is
of such length also that it spans the third triangle from the end, and in some
cases it may be even longer. For the third triangle, an additional bar or
series of bars overlapping those of the second triangle is provided, and of such
dimensions that with the bar or bars already reaching along the third triangle
the exact requisite section shall be provided. In this way the lower hori-
zontal member of the girder is formed of a series of overlapping bars or links
of such size and so arranged that the exact requisite section shall be provided
in each triangle. The several bars or links are connected together and
support the diagonal members of the girder by means of connecting pins in
the usual manner. It may or may not be necessary to complete the requisite
section of the middle triangle (where there is an odd number of triangles) by
links spanning the length of that triangle only.
It will be understood that if instead of the several triangles of a Warren
girder, the girder be a truss with rectangular panels, my improvements may
be applied to this also. The same general application of overlapping bars
may be made also to the upper horizontal or compression member of various
bridge girders or trusses, and also to iron roofs, the trusses of which are of
analogous construction.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Joseph Westwood in the Great Seal Patent Office on the
21st June 1865.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, JOSEPH
WESTWOOD, junior, of Tredegar House, Bow, in the County of Middlesex, send
greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Twenty-first day of December, in the year of our Lord
One thousand eight hundred and sixty-four, in the twenty-eighth year of
Her reign, did, for Herself, Her heirs and successors, give and grant unto
me, the said Joseph Westwood, Her special licence that I, the said Joseph
Westwood, my executors, administrators, and assigns, or such others as I, the
said Joseph Westwood, 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

page_text: Ireland, the Channel Islands, and Isle of Man, an Invention for "IMPROVE-
MENTS IN IRON BRIDGES," upon the condition (amongst others) that I, the
said Joseph Westwood, my executors or administrators, by an instrument
in writing under my, or their, or one of their hands and seals, should par-
ticularly describe and ascertain the nature of the said Invention, and in
what manner the same was to be performed, and cause the saine to be filed
in the Great Seal Patent Office within six calendar months next and imme-
diately after the date of the said Letters Patent.
NOW KNOW YE, that I, the said Joseph Westwood, do hereby declare
the nature of my said Invention, and in what manner the same is to be
performed, to be particularly described and ascertained in and by the following
statement :-
These improvements are more particularly applicable to the lower
horizontal members or tension chains of the variety of iron bridge girder for
which James Warren and Willoughby Theobald Monzani obtained Letters
Patent, dated August 15, 1848, No. 12,242; but these improvements are
also applicable to the upper tables or horizontal compression members of the
same variety of bridge girders, and they may be applied with a certain degree
of advantage to both the upper and the lower flanges of certain other varieties
of girders.
It is well known that the requisite strength of the upper and lower
horizontal members or flanges of a bridge girder or truss increase pro-
gressively from the ends towards the middle of their length. In Warren's
girders the requisite strength of the horizontal tension links, for example,
increases in each triangle from the ends to the centre or mid span. Where
the triangles in a Warren girder are large, it is usual to provide the requisite
strength with as much exactness as is practicable in each triangle. Where
the span is short, it is usual, for convenience of construction, to employ tension
links of a length sufficient to span two or more triangles. In this case, as the
links have the same section throughout their whole length, the distribution
of iron is not exactly that due to the strain in the several triangles, and hence
there is a waste of material. Where, in larger triangles, the section of the
links is exactly that proper for the strain in each triangle, there is still a loss
of metal in the " overlaps" of one set of links in each triangle past and
beyond the ends of the links in the adjacent triangles. There is also in this
case a greater amount of drilling required in forming the holes for the pins
which connect the links together into the lower tension member of the girder
than where the same links extend over two or more triangles; and the pins
for connecting the links together are longer and consequently heavier where

page_text: there is a separate set of links for each triangle than where the links each
cover two or more triangles.
.
Now, my improvements in iron bridges, especially when applied to the
lower or tension members of Warren's girders, permit of the exact requisite
distribution of iron in the links of the triangle, and I am furthermore enabled
to save a considerable part of the iron now wasted in overlaps at the con-
necting pins, and I obtain also the least permissable length and weight of
the connecting pins themselves; and, furthermore, whereas the lower or
tension members of a Warren's girder, as commonly made, are flexible chains
having free vertical movement upon their connecting pins, the lower member
of a like girder upon my improved construction would have a considerable
degree of vertical stiffness of itself, even when unconnected with the other
parts of the girder, and it could be erected, therefore, with less staging or
other temporary support.
The mode which I adopt for forming the lower or horizontal tension
member of a Warren girder is as follows, the description proceeding from
either end towards the middle of the length of the girder:-I take one or
more bars of a section or collective section proper for the lower tension link
of the end triangle, but of a length sufficient to span horizontally along two
or more triangles. Along that portion of the length of this bar or these bars
which corresponds to the second triangle from the end of the girder I apply
another bar or bars of such section that, together with the first bar or bars
described, the second bar or bars shall give the exact requisite strength for
the lower tension member or links of the second triangle. The second bar or
series of bars is of such length also that it spans the third triangle from the
end, and in some cases it may be even longer. For the third triangle, an
additional bar or series of bars overlapping those of the second triangle is
provided, and of such dimensions that with the bar or bars already reaching
along the third triangle the exact requisite section shall be provided. In this
way the lower horizontal member of the girder is formed of a series of over-
lapping bars or links of such size and so arranged that the exact requisite
section shall be provided in each triangle. The several bars or links are con-
nected together and support the diagonal members of the girder by means of
connecting pins in the usual manner. It may or may not be necessary to
complete the requisite section of the middle triangle (where there is an odd
number of triangles) by links spanning the length of that triangle only.
It will be understood that if, instead of the several triangles of a Warren
girder, the girder be a truss with rectangular panels, my improvement may be
applied to this also. The same general application of overlapping bars may

page_text: be made also to the upper horizontal or compression member of various
bridge girders or trusses, and also to iron roofs, the trusses of which are of
analogous construction.
The annexed Sheet of Drawing shows, in plan and elevation, a girder made
with my improvements. In the example shown the span is 66 feet and the
thickness of the respective bars is marked upon the Drawing.
In witness whereof, I, the said Joseph Westwood, junior, have hereunto
set my hand and seal, this Twenty-first day of June, in the year of our
Lord One thousand eight hundred and sixty-five.
JOSEPH WESTWOOD, JUN. (L.S.)
Witness,
ZERAK COLBURN,
7, Gloucester Road,
Regent's Park, N. W.