When Uncle Ed saw it he showed us at once where
the trouble lay. Our intermediate cross beams were hung from the center of
the spars, and consequently made them bend, because the strain came across
their length, while at the center of the bridge there was no chance for
the spars to bend, because the strain was exerted along their length, that
is, it tended merely to push the ends of the spars deeper into the banks.
To remedy the trouble he proposed propping up the center of each spar with
a brace running from the center crosspiece. The dotted lines in Fig. 100
show how these braces were applied. They made the floor perfectly solid
throughout, and gave the bridge a much better appearance. Uncle Ed told us
that the structure might be called a "king rod truss," except that in
place of rods we had used wires.
The King Post Bridge.
The other bridge on the Schreiner property was built in the following
summer, just before we started on our second expedition to Willow Clump
Island. It spanned the brook at the gorge, and was therefore a more
difficult engineering feat. Mr. Schreiner himself asked us to build it,
and we felt greatly honored by the request. A search was made in the Van
Syckel library for a suitable type.
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