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240 STRENGTH OF MATERIALS.
a beam supported under both ends and loaded at the center;
therefore, Fig. 9.
8 X CX H*X B
For a beam fixed at both ends
and loaded at the center,
P = 8 X CX H* X B
For a beam fixed at both ends
and the load distributed evenly
throughout its whole length,
P = 12 X C X H* X B
Each letter in these formulas has the same meaning as in
formula for Fig. 6, page 239, and each formula may be transposed
the same as that formula. The most convenient way is, in each
case, to multiply the numerical value of Cfrom Table No. 30, by
its proper coefficient according to mode of loading, before it is
inserted in the formula.
Note.—A square beam laid in this position has 40 %
more transverse strength than the same beam laid in
this position.
TABLE No. 30. — Constant C.
Giving the weight in pounds which will break a beam one
foot long and one inch square which is fastened at one end, in a
horizontal position, and loaded at the other end.
Material. Very Good. Medium. Poor.
Wrought iron,*
Cast-iron,
Spruce and Pine,
Pitch pine,
Granite,
750
650
160
225
600
500
125
150
25
500
400
90
100
* A wrought iron beam or bar will not actually break under these conditions,
but, as it will bend so much that it becomes useless, it is considered to be equivalent
to the breaking point.
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