90 THE KANSAS CITY BRIDGE.

The draw span was raised on false-works extending from the pivot pier to the
upper and lower rests. As the small amount of sand above the rock precluded
the driving of piles, these works were built on cribs, two of which, loaded with
stone, were placed between the pier and each rest. These cribs were originally
intended to serve as the foundation of a permanent draw protection ; they were
built in the winter of 1868-9 ; were made thirty feet square, and divided by four
cross-walls into nine compartments. The deadening effect of the upper rest and
pier on the current, had so checked the scour that the cribs did not settle to the
rock, and as their bearing was not thought to be firm enough to carry a perma-
nent structure, they were built up above ordinary high-water, and a wooden
truss, strong enough to sustain itself if the cribs settled, and which should
serve as false-works for raising the draw, was built upon them.*

As soon as Pier No. 2 had been completed, the pivot was placed upon it,
and the turn-table put together ; the chords were then spread out and riveted,
. and the bridge trusses made self-sustaining at the earliest possible moment, the
whole structure being raised in about six weeks. The cribs settled slightly under
the weight of iron, but not enough to give trouble, the subsidence being remedied
by additional blocking. Since then the upper cribs have not settled materially,
and are probably on their permanent bearing ; but the night after the weight
of the truss had been taken off the false-works, a rise in the river scoured
around the two lower cribs, causing them to settle away from the truss ; under
the continued scour of the summer flood they continued to settle, tilting from
side to side, and finally, when the flood was at its height, they tipped over and
rolled away ; the false-work truss remains standing, and no harm was done to
the works.

On the occasion of the public opening on the 3d of July, the bridge was
tested in the presence of a number of engineers invited to examine it, with the
following results :—

176 FOOT SPAN.

Load at North quarter of Span... ..- 2.2.3. cecceecenscccsapensrgens 46 Tons.
North quarter Defloction 1... 22... es cee sss c were cscces 44 Inch.
Centre We OC Gat ee web we cena wea bees oes b ae ke 419“

Load at Centre and Nort quarter’ .....:..06 004 se secersccoedaecees 92 Tons.

* The temporary Draw Protection is shown on Plate VII.