The braced frames, he wrote, were those
which would be under a compression strain, while the others would be under
tension; that is, when any weight was placed on the bridge it would push
against, the ends of the braced frames, trying to crush them, but would
pull on the unbraced frames, trying to tear them apart. In fact, the
bridge would have been just as strong had we used heavy iron wire in place
of the unbraced frames, and the only reason Uncle Ed did not recommend our
doing so was because we had no simple way of stretching the wire taut.
Erecting the Towers.
[Illustration: Fig. 315. K Frame (make one).]
[Illustration: Fig. 316. L Frame (make two).]
We built the complete set of frames before attempting to erect the bridge.
Then we began by building the towers. Two A frames were set on end and
spaced 4 feet apart at the top and 5 feet apart at the bottom, measuring
not from the inner but from the outer edges of the frames. In this
position they were connected by short spars, notched in place. The notches
for these connecting spars will be seen in Fig. 305 on the main or
vertical timbers of frame A, just below the upper and middle cross sticks
and above the lower cross sticks.
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