side, or facing the towers, as will be clearly understood
by examining the illustrations. As soon as the
B and C frames were set up on one side of the tower,
another pair of B and C frames was set up on the other
side of the same tower. A cantilever bridge must
always be built out on both sides of the tower at
the same time, otherwise it will be overbalanced on
one side and topple over. After the B and C frames
were in place we took two D frames, with oppositely
cut ends, and rested their tie sticks on the top of
the tower, just under the ends of the C frames.
The ends of the two D frames overlapped at the center
of the tower, and, as one was cut away at the outer
side and the other at the inner side, they fitted neatly
together and were fastened with bolts. The D
frames were supported near their outer ends with E
frames, which rested on the B and C frames. Fig.
319 shows an E frame set in position on the landward
side of the tower, while two of the boys are climbing
out on the opposite B and C frames preparatory to
setting up the other E frame. A cross stick was
now bolted to each D frame, just beyond the upper
ends of the E sticks. This done, the frame F
was hooked in between the ends of B and C, at the shoreward
side of the tower, and its outer ends were supported
by frame G, which was hooked over frame D and the
upper ends of frame E. The frame L was then rested
on the ends of frame F and G, and supported the shore
end of frame D. A stick nailed across frame D on each
side of the upper ends of frame L served to hold the
latter in place.
Binding and Anchoring the Structure.
As the different frames were coupled together, we
bound the overlapping ends with soft iron wire.
The place where frames B, C, E and F came together
was quite a vital point, and we took pains to make
the wire binding at this place doubly strong.
As soon as the L frame was in place we anchored the
bridge to shore by running wires from the ends of the
D frame and the ends of the G frame to stakes driven
into the banks. The frames on the second tower
were now similarly erected and anchored, after which
we were ready to put in the center panels of the bridge.
[Illustration: Fig. 319. Preparing to Put
an E Frame in Place.]
The Center Panels of the Bridge.
First, the frame H was wedged into place and thoroughly
fastened by a liberal winding of wire. Next the
frames I and J were set in place, and in order to
do this we had to remove the upper tie pieces of these
frames. Then one frame was hooked in the other,
and the two were carried out on the scow under the
center of the bridge. Ropes were tied to the ends
of the two frames, and they were lifted together,
like a wide V, to the position shown in Fig. 318,
after which the tie pieces were bolted on again, resting
against the ends of the E frames. As an additional
security, two sticks were bolted to the under side
of the frame H, one at each side of the I and J frames.