k Truss.]

In both England and America in early braced bridges cast iron, generally in
the form of tubes circular or octagonal in section, was used for
compression members, and wrought iron for the tension members. Fig. 19
shows the Newark Dyke bridge on the Great Northern railway over the Trent.
It was a pin-jointed Warren girder bridge erected from designs by C.M. Wild
in 1851-1853. The span between supports was 259 ft., the clear span 2401/2
ft.; depth between joint pins 16 ft. There were four girders, two to each
line of way. The top flange consisted of cast iron hollow castings butted
end to end, and the struts were of cast iron. The lower flange and ties
were flat wrought iron links. This bridge has now been replaced by a
stronger bridge to carry the greater loads imposed by modern traffic. Fig.
20 shows a Fink truss, a characteristic early American type, with cast iron
compression and wrought iron tension members. The bridge is a deck bridge,
the railway being carried on top. The transfer of the loads to the ends of
the bridge by [v.04 p.0541] long ties is uneconomical, and this type has
disappeared. The Warren type, either with two sets of bracing bars or with
intermediate verticals, affords convenient means of supporting the floor
girders. In 1869 a bridge of 390 ft. span was built on this system at
Louisville.

Amongst remarkable American girder bridges may be mentioned the Ohio bridge
on the Cincinnati & Covington railway, which is probably the largest girder
span constructed. The centre span is 550 ft. and the side spans 490
ft.--centre to centre of piers. The girders are independent polygonal
girders. The centre girder has a length of 545 ft. and a depth of 84 ft.
between pin centres. It is 67 ft. between parapets, and carries two lines
of railway, two carriageways, and two footways. The cross girders,
stringers and wind-bracing are wrought iron, the rest of mild steel. The
bridge was constructed in 1888 by the Phoenix Bridge Company, and was
erected on staging. The total weight of iron and steel in three spans was
about 5000 tons.

[Illustration: FIG. 21.--Typical Cantilever Bridge.]

[Illustration: FIG. 22.]

10. (e) _Cantilever Bridges._--It has been stated that if in a girder
bridge of three or more spans, the girders were made continuous there would
be an important economy of material, but that the danger of settlement of
the supports, which would seriously alter the points of contrary flexure or