108 THE KANSAS CITY BRIDGE.

each triangle equal to the difference between the expansions of the tie and
brace, and causing a deflection at the centre equal to

140 dX [.000837 — 000272] =.079 = 14 inches.

The total deflection caused by an increase of temperature of 120° will therefore
be .229 feet, or 2% inches.*

The extreme vertical variation of the centre of the span, from its position
when unloaded at the lowest temperature, and when fully loaded at the highest
temperature, will not exceed .373 feet, or 445 inches.

The deflections of the other spans may be calculated in the same manner,
but will be less than the above. The calculations for the 176 and 130 ft. spans
are much simplified by the absence of curvature in the upper chords.

STRAINS IN THE DRAW.

The weight of the iron and timber in the draw is 735,000 pounds; the
turn-table, entirely of iron, weighs 52,000 pounds, leaving for the weight of the
trusses and floor 683,000 pounds. The length of each truss between the centres
of the end posts is 359.3 ft., making the dead load 1,901 pounds to the foot; a
small allowance should be added to this for paint, wire railing, dust, ice, etc.,
increasing the dead load to 1,920 pounds per foot, which leaves a simple ratio
to the assumed moving load of 2,240 pounds to the foot. The framing of the
truss is such that the weight should be transferred to the turn-table only through
the centre posts and cross-girders, the adjoining posts standing outside of the
turn-table ; the length of each arm should therefore be measured from the
centre of the truss. The skew of the bridge makes the two arms of each truss
of unequal length; the greater length, 182 feet, will be considered in these cal-
culations, giving results which will be slightly excessive for the shorter arm.
The total load per running foot on each truss is 2,080 pounds, of which ;°,, or
960 pounds, is dead, and 1,120 is variable.

* The noted expansion of bottom chords from the coldest day in January, 1870, say 10° below zero, to the
warmest day in June, 1870, say 104° above in the shade, was as follows:

AQSMG BpaM . SFE ae. +5 inches. 250 ft. span..... eee ee eee eee 18 inches.

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