Improvement in the Construction of Bridges, 
Description of the Plates, with Definitions of 
technical terms, &e. 
Numbers 1, 2, and 3 exhibit all the parts of a 
bridge on the last improvement, with suspension 
posts, &c., suited to a span of 170 to 220 feet, 
according to the size and number of its parts, 
which may be so varied as to suit the width of 
span required. 
Definitions, Explanations and General Re- © 
marks,—I1st. A truss is that combination (No. 2) 
of materials, which, with one or more other sim- 
ilar ones, constitute the whole vertical support of 
the bridge. They are placed in a vertical posi- 
tion on the piers, and are kept so by the addition 
of bottom beams, top beams, and horizontal and 
side braces, as shown in No. 
These few parts may be'termed the skeleton 
_ of the bridge, and constitute the whole strength 
and support of the superstructure; to which a 
floor is added, for the conveyan 
duce, goods, &c., and generally a roof and side 
covering, to save the skeleton and floor from that 
decay which is incident to its exposure to the 
Weather. ‘ 
. Truss-braces, or diagonal braces, are those § 
crossing each other, and forming the truss into 
diamonds. There are two series or sets of such 
truss-braces, separated by middle string-pieces, 
six or seven inches thick. (See figs. 1 and 2.) 
Each series of truss-braces may be termed a lat- 
‘tice; hence it is, by some, termed the double 
lattice bridge. The diamond-truss bridge, double 
diamond-truss, or double diamond brid 
be more appropriate and better understood. 
3d. String-pieces are all those horizontal parts 
of a truss, at top and bottom, or intermediate, 
which run the whole length, and are secured to 
the truss-braces’ by three or four tree-nails, at 
each intersection of them, over which the string- | 
eces 
i . . 7 . * 
4th. Intermediate string-pieces are those which 
pass over the lines of intersections of the truss-bra- 
braces, whether at top, at bottom, or intermedi- 
ate; intermediate middle ones only, are here 
represented 
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293 
