d | 209 | 24.5 |
| Black willow | 193 | 22.6 |
|-------------------------------------------------------|

The complexity of the computations depends upon the way in which
the stress is applied and the manner in which the stick bends.
Ordinarily where the length of the test specimen is not greater
than four diameters and the ends are squarely faced (see Fig.
7), the force acts uniformly over each square inch of area and
the crushing strength is equal to the maximum load (P) divided
{ P }
by the area of the cross-section (A). { C = --- }
{ A }

[Illustration: FIG. 7.--Endwise compression of a short column.]

It has been demonstrated[4] that the ultimate strength in
compression parallel to the grain is very nearly the same as the
extreme fibre stress at the elastic limit in bending. (See Table
V.) In other words, the transverse strength of beams at elastic
limit is practically equal to the compressive strength of the
same material in short columns. It is accordingly possible to
calculate the approximate breaking strength of beams from the
compressive strength of short columns except when the wood is
brittle. Since tests on endwise compression are simpler, easier
to make, and less expensive than transverse bending tests, the
importance of this relation is obvious, though it does not do
away with the necessity of making beam tests.

[Footnote 4: See Circular No. 18, U.S. Division of Forestry:
Progress in timber physics, pp. 13-18; also Bulletin 70, U.S.
Forest Service: Effect of moisture on the strength and stiffness
of wood, pp. 42, 89-90.]

|-------------------------------------------------------------------------------|
| TABLE V |
|-------------------------------------------------------------------------------|
| RELATION OF FIBRE STRESS AT ELASTIC LIMIT (r) IN BENDING TO THE CRUSHING |
| STRENGTH (C) OF BLOCKS CUT THEREFROM, IN POUNDS PER SQUARE INCH |
| (Forest Service Bul. 70, p. 90) |
|-------------------------------------------------------------------------------|
| LONGLEAF PINE |
|-------------------------------------------------------------------------------|
|