IMPROVEMENTS IN THE CONSTRUCTION OF IRON BRIDGES
Year: 1857

page_text: by the Act.)
PROVISIONAL SPECIFICATION left by John Henry Johnson at the Office
of the Commissioners of Patents, with his Petition, on the 2nd October
1857. A communication from Francis C. Lowethorp, of the City of
Trenton, in the County of Mercer, in the State of New Jersey, and the
United States of America.
I, JOHN HENRY JOHNSON, of 47, Lincoln's Inn Fields, in the County of
Middlesex, and of 166, Buchanan Street, in the City of Glasgow, North
Britain, Gentleman, do hereby declare the nature of the said Invention for
"IMPROVEMENTS IN THE CONSTRUCTION OF IRON BRIDGES," a communication from
Francis C. Lowethorp, of the City of Trenton, in the County of Mercer, in
the State of New Jersey, and the United States of America, to be as
follows:-
The first part of this Invention relates to the construction of that class of
bridge known by the name of truss-frame girder bridges, and consists in
so constructing, arranging, and connecting the upright posts thereof that
they may be free to vibrate in the upper and lower chords. To effect this, I
propose to round the top of the upright posts, such rounded tops fitting into
caps with recesses formed in them for that purpose, and in such manner that
the posts can vibrate without moving the caps, but have no other movement

page_text: independent of the caps. In the lower end of each of the outer posts is
formed a recess, which fits on a rounded projection cast in the metal founda-
tion plates, and each of the lower ends of the other or intermediate posts is
also recessed to fit on a rounded projection cast on metal combination plates,
such projections being so formed as to allow the posts to have a vibrating
motion. The caps in which the upper ends of the posts vibrate, are made so
as to have, at one side, a projection, and at the other a recess, for the purpose
of fitting into corresponding recesses and projections at the ends of the
straining picces, the junction of the caps and the straining pieces being on
one side rigid, and on the other free. The upper part is made with a
moulding or projection at each side, for the purpose of affording a hold for
the bent lips of a shoe piece, which has a recess cast upon its upper side to
receive a longitudinal beam, the beam and shoe piece being bolted together.
The shoe pieces are so fitted to the cap, that they can have a longitudinal
movement communicated to them without conveying that motion to the cap.
The diagonal and counter-diagonal tie rods are connected by simple eyes
to bolts, one of which bolts passes through and is secured to each of the caps,
the head of such bolt forming an eye, whereto are jointed the transverse struts
and diagonal tie rods, which serve to connect the caps of the opposite truss
frame to each other, and to steady the whole. The lower chord rods are
connected to the metal plates, on which the posts vibrate by means of screw
threads and lengthened nuts. Rods are arranged at each end of the girders,
which rods serve to retain them in position, and are secured by nuts to
foundation plates, and these are secured to the foundation or piers, such
plates being formed to receive the lower ends of the end posts, as before
mentioned, and are made adjustable, to allow for expansion and contraction
occasioned by variations of temperature. The flooring of the bridge may
either be supported on the caps in connection with the top chord, or arranged
in any suitable manner on the lower chord.
The second part of this Invention relates to improvements in suspension
bridges, and consists in using upright posts, similar in construction to those
used in my improved truss-frame girder bridge; the bottoms of such posts
are arranged to vibrate in plates secured to the floor or lower chord in
any suitable manner, to which plates are also jointed the lower ends of the
diagonal tie rods. The top of the posts, which are rounded, work in
recesses formed on the underside of combination plates, to which plates
are also connected the upper ends of the diagonal tie rods by pins or bolts.
These combination plates are also furnished with four short rods, which fit

page_text: loosely in holes made therein, and allowed to project a short distance on each
side; the ends of these rods are screwed, and are furnished with lengthened
nuts, into which are secured the screwed ends of the suspension or upper
chord rods.
The rods which form the cable are connected to the suspension or upper
chord rods and to the top of the tower, in a similar manner.