\fdO'^ - Old Forge Coal Mines

210 STRENGTH OF MATERIALS.
P- p-^^. „, 4-^^- ^X^X^-QQQ
or A- - .8727272 8727272 so sq. in in.
-^, ~^-- ^^^
(562) From Table 19, the weight of a piece of cast iron
1' square and 1 ft. long is 3.125 lb.; hence, each foot of
length of the bar makes a load of 3.125 lb. per sq. in. The
breaking load-—that is, the ultimate tensile strength— is
20,000 lb. per sq. in. Hence, the length required to
the bar is ^^
break
= 6,400 ft. Ans.
(563) Let / = the thickness of the bolt head;
d = diameter of bolt.
Area subject to shear = t: d f.
Area subjected to tension = —izd'^.
4
S^ = 55,000. 5, = 50,000.
Then, in order that the bolt shall be equally strong in both
=^ o,, = ^.=|2qM00^.200'. Ans.
4:T:dS^ 4.S, 4 X 50,000
tension and shear, t: d t S^ = —Tt d"^ S^,
(564) Using a factor of safety of 15 for brick, formula
65 gives
15
A = {2^X 3^) sq. ft. = 30 X 42 = l.,260 sq. in. ; S^ = 2,500.
Therefore, P= 1>^^0 X ^^^00 ^ ^10,000 lb. = 105 tons. Ans.
(665) The horizontal component of the force Pis Pcos
30° = 3,500 X .866 = 3,031 lb. The area A is i a, the ultimate
shearing strength, S^, 600 lb. and the factor of ,
safety, 8.
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