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STRENGTH OF MATERIALS. 227
smallest side. Find the quotient in the column headed -p-
and find the safe load per square unit of area in the cor-
responding column of the table. Multiply this by the metal
area of the pillar, and the product is the safe load, with 10 as
factor of safety, on a pillar well fitted and having square ends.
For any other kind of ends and any other unit of safety, allow-
ance must be made as explained on previous pages.
Example 1.
Find the safe load in pounds, according to Table No. 27,
for a round, hollow, cast-iron pillar five feet long, five inches
outside and four inches inside diameter, having square ends
well fitted and being evenly loaded.
Solution:
Five feet equals 60 inches, and 60 divided by 5 gives 12.
In the first column, under the heading " Length divided by
diameter, or smallest side, " is 12, and in that line, in the column
headed " pounds per square inch " for hollow cast-iron pillars,
is 5882. The metal area of this pillar is obtained by subtract-
ing the area of a circle four inches in diameter from the area of
a circle five inches in diameter (see area of circles, page 196;
Table, page 209), which is 19.63—12.57 — 7.06, or practically
seven square inches, and seven times 5882 equals 41,174 pounds.
Example 2.
Find the safe load in kilograms, according to Table No. 27,
for a round spruce post 2 meters long and 20 centimeters in
diameter.
Solution
:
Two meters = 200 centimeters and ^ = 10. The corre-
sponding constant in the table is 25 kilograms. The area of a
circle 20 centimeters in diameter is 314.2 square centimeters,
and 25 times 314.2 = 7855 kilograms, as safe load.
Example 3.
What would be the safe load on the same post if it had
been 20 centimeters square, instead of round ?
Solution
:
The length is the same ; therefore the length divided by the
side gives 10, as before, and the corresponding constant is 25
kilograms, but as the cross-sectional area in square centimeters
is 20 X 20 = 400, the corresponding load will be 400 X 25 —
10,000 kilograms as the safe load.
Note.—It will be noticed that in figuring the strength of
pillars according to this table, the strength of a square pillar
will always be to the strength of a round pillar as 1 to 0.7854,
while theoretically the strength of a square pillar compared to
that of a round pillar will vary with the length, the extremes
being 1 to 0.589 for extremely long pillars and 1 to 0.7854 for
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