IMPROVEMENTS IN THE CONSTRUCTION OF BRIDGES, VIADUCTS, GIRDERS, AND OTHER STRUCTURES OF LIKE CHARACTER
Year: 1871

page_text: PROVISIONAL SPECIFICATION left by Sir Thomas George Augustus
Parkyns at the Office of the Commissioners of Patents, with his
Petition, on the 31st March 1871.
I, Sir THOMAS GEORGE AUGUSTUS PARKYNS, of Gloucester Square,
Hyde Park, in the County of Middlesex, Baronet, do hereby declare the
nature of the said Invention for "IMPROVEMENTS IN THE CONSTRUCTION OF
BRIDGES, VIADUCTS, GIRDERS, AND OTHER STRUCTURES OF LIKE CHARACTER," to be
as follows:-
This Invention relates to the construction of bridges, viaducts, girders,
and other structures of like character, the object being to support the
roadway and load which such structures may have to sustain by means
of one or a number of wire cables or straight lengths of wire (by pre-
ference steel), formed into bundles and stretched tightly across the
span or space to be bridged over, the strength of the bridge, viaduct,
or other like structure depending upon the great tensile strain which
wire cables of this character are calculated to bear. In place of wire
cables the longitudinal ties may be metallic tubes, or other suitable
materials, according to the nature of the structure to which they are
applied.

page_text: In constructing a bridge or viaduct in accordance with my im-
provements I place skewbacks, resistance blocks, frames, or abutments
on each side of the span of suitable strength to resist the strain to
which they are likely to be subjected. These skewbacks, resistance
blocks, frames, or abutments may be formed or constructed in various
ways depending upon the character of the structure for which they
are required, but I prefer to form them with arched or curved back
surfaces to resist the strain put upon them by the cables. The skew-
backs, resistance blocks, frames, or abutments are connected across
the span by means of girders, arched or otherwise, the construction of
which will also depend upon the magnitude or character of the work
to which my improvements are applied, such girders serving to prevent
the sagging of the floor or platform, and in conjunction with the floor
or platform to keep the skewbacks, resistance blocks, or abutments
in position and prevent them from being drawn towards each other
by the strain put upon them by the cables, and I prefer the cables or
their equivalents to be so far strained that the upper portion of the
girders may be in a condition of tension, and the lower portion in a
state of compression, but this condition is not absolutely essential.
Between the side girders longitudinal rafters of timber or plates of
iron or other metal, or metal and timber combined are arranged and
kept apart by means of spacing blocks, through which transverse ties of
metal are passed from girder to girder and the whole structure is thus
firmly bound together. Transverse trussed beams may be employed to
prevent sinking in the case of a wide floor. The cables which connect
the skewbacks, resistance blocks, or abutments before they are stretched
tightly across the span are supported upon the spacing blocks between
the longitudinal timbers or other bearers to prevent the cables from:
sagging, and in some cases they may be supported throughout their
entire length if requisite by boards or metal plates. The ends of the
cables, or the means of straining them, pass through the skewbacks,
resistance blocks, or abutments at each end of the girders, and the cables
are strained to the degree of tightness required by means of windlasses,
screws, or other mechanical means, and are firmly secured in that.
condition in any convenient manner. The skewbacks, resistance blocks,
or abutments at each end of the girders may rest upon rollers placed on
the piers which support the structure or be otherwise arranged to allow.
for expansion and contraction. In cases where desired and where more
than one cable or stretcher is used access may be easily had to the whole,

page_text: series, and the number employed may be of such collective strength
that one or more of them may be removed for repair without derange-
ment of the structure. In some cases a portion of the load may be made
to rest or be supported upon or by the cables direct, as it is evident that
the amount of their combined strength may be increased to any desired
extent, and the means of so supporting the load may be greatly varied,
but it is preferable to support the load as previously described. Besides
the two side girders above named there may in the case of wide
bridges or other structures be one or more like girders which may be
placed as required.