110 THE KANSAS CITY BRIDGE.

the strains due to the weight of the live load alone, the latter component strains
being simply those caused by a load of the given intensity on an isolated span
182 feet long, and.being tensile strains in the lower chord and compressive in
the upper. The moment of flexure at the centre of the arm, due to the mov-
ing load only, is :-—
ae — 4,637,360 pounds.

and the moments throughout the arm will be proportional to the internal ordi-
nates of a parabola.* The resulting moments, the effect of the dead and live load
combined, being at each point equal to the algebraic sum of the two moments
already considered, are negative at the centre of the draw, decreasing in intensity,
and finally becoming positive as they approach the end of the loaded arm.+

As the train advances upon the second arm, this arm will begin to deflect
until it takes a bearing upon the wedges, while the strain over the pivot, which
has hitherto remained unchanged, begins to increase. After an end bearing has
been taken upon the wedges the second arm will continue to deflect at inter-
mediate points until the entire draw is loaded,
when the deflection of the two arms becomes
symmetrical, and the distortions of the beam
resemble those shown in Fig. 8. The strain

 

over the pivot does not attain its greatest intensity until both spans are fully
loaded ; it is then equal to the sum of the effects due to the dead load, which
is carried wholly by the pivot pier, plus the effects of the live load, which is dis-
tributed according to the laws which govern a continuous beam resting on three
supports. The moment due to the moving load, is at the centre the negative of
that at the centre of one arm when loaded alone, being equal to

— 4,637,360 pounds.t

this added to the moment due to the dead load gives for the maximum moment

at the centre
— 20,536,880 pounds.

 

* Shown on the diagram in a dotted line ..........
+ The curve of these moments is given on the diagram ina broken line — — —— —
{ The curve of these moments is shown on the diagram in a broken line —...—-...—...--...