The Locomotive - Lighthouse Survival Blog
The Locomotive - Lighthouse Survival Blog
The Locomotive - Lighthouse Survival Blog
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1901.] THE LOCOMOTIVE. 115<br />
way, but must give out simultaneously at both of the sections named. If these sections<br />
were a considerable distance apart, we could consider the resistance of the pin to double<br />
shear (that is, to simultaneous shear in two different places) to be double its resistance<br />
to shear in one place only; and this would mean that it would suffice to make the sec-<br />
tional area of the pin 1.13-^-2=0.59 times as great as the sectional area of the body of<br />
the brace. But it is known from experiment that the resistance of iron or steel to dou-<br />
ble shear is not twice as great as its resistance to single shear, when the sections across<br />
which the failure occurs are near enough together for the stresses in the vicinity of one<br />
of the sections to be felt to a considerable extent at the other qne. This condition<br />
holds true in most of the brace pins that we find in stationary boilers; and it is found,<br />
— \7<br />
^7<br />
—<br />
^7 V r<br />
Figs. 3 and 4. — Showing Possible Ways in which the Load may be Thrown<br />
on the Pin.<br />
experimentally, that the resistance of a rivet or pin or bolt to double shear along two<br />
planes that are near together is only about 1.85 times as great as the resistance of the<br />
same pin or rivet or bolt to single shear. Hence, instead of dividing 1.18 by 2, we<br />
must divide it by 1.85; and upon doing so we find that it will be sufficient to allow<br />
1.18-^1.85=0 64 sq. in. of sectional area to the pin, for every square inch of sectional<br />
area in the body of the brace. Now the diameters of two cylindrical bodies (like the<br />
pin and the brace body) are to each other as the square roots of the sectional areas<br />
of these bodies; and as the square root of 0.64 is 0.8, our final conclusion is, that a<br />
brace pin, arranged as shown in Fig. 1, will be strong enough to resist shear alone, if<br />
the diameter of the pin is not less than 0.8 of the diameter of the body of the brace.<br />
In the present case the body of the brace is 1% in. in diameter, or 1.375 in. Hence<br />
the diameter of the brace pin must not be less than 1.375x0.8 = 1.100 in., which is<br />
a trifle under 1| in.
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