Bearing strength of wood at angle to the grain

IEAIPINI STR1[NfThl 0f W4(11[

AT ANCL[ TV TUC 1RAIN


No. 1203
IRevised March 1956


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i U DEPOSITORY


HUME LIBRARY
Ocr i, 1972

F.A.S. jiv. of Floni.a"

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FOES PRDUT LABORATOR
FO ES SERVICE*
MADION 5 WISONSI


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BEARING STRENGTH OF WOOD AT ANGLE TO THE GRAINI


By

Forest Products Laboratory,2 Forest Service
U. S. Department of Agriculture





The compressive strength of wood depends on the direction of the grain
with respect to the direction of the applied force. It is highest
parallel to the grain and lowest perpendicular to the grain, and for
other angles has intermediate values. The ratio between the values
perpendicular and parallel to the grain are not the same for different
species of wood and also vary with the method of applying the load. For
example, the basic stress of Douglas-fir is 1,450 pounds per square inch
parallel to the grain and 2355 pounds perpendicular to the grain, while
for oak these respective values are 1,550 and 3565. The safe load on a
1-inch bolt in a 6-inch Douglas-fir timber is 5,8-40 pounds parallel to
the grain and 2,440 pounds perpendicular to the grain.

On account of this variation in the magnitude and relationship of the
compressive strength parallel and perpendicular to the grain, the
determination of the proper value for intervening angles has always been
a difficult problem in timber design. To present values in tables for
all the conditions would be impracticable. The bearing values for inter-
vening angles, therefore, are usually obtained from the values parallel
and perpendicular to the grain by the use of the Hankinson formula. This,
however, involves a separate calculation for each individual condition
and in order to provide a more convenient method the accompanying nomo-
graph, based on the formula, has been developed by John A. Scholten of
the U. S. Forest Products Laboratory.

The nomograph is based on the Hankinson formula, which is considered
most applicable by the U. S. Forest Products Laboratory.

By means of this nomograph the stress or load for any intervening angle
can be obtained from the stress or load parallel and perpendicular to the
grain without any calculation. The symbols in the chart are represented

1
-Original report by J. A. Newlin, Specialist in the Mechanics of Wood,
published in Engineering News-Record May 11, 19359.
Maintained at Madison, Wis., in cooperation with the University of
Wisconsin.


Agriculture-Madison


Rept. No. 1203


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by allowable loads or stresses, but the formula is applicable for loads
or Btr-sr..i1-, ge-nerally. The intercepts on any vertical line are pro-
portional to sin2Q from 0 to 90 degrees. The scale of the chart was
ch'u-L'ri primarily for convenient use with bolt loads, but for greater
or lesser VLlues8 or for different units, the m.-:initude of the scale can
be ,.]just',d to obtain greater accuracy without affecting the chart's
applicability.


Rept. rNo. 1203


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>, LEGEND
S/P= ALLOWABLE LOAD OR STRESS PARALLEL TO GRAIN.
0-=ALLOWABLE LOAD OR STRESS PERPENDICULAR TO GRAIN.
N=ALLOWABLE LOAD OR STRESS AT INCLINATION 0 WITHi THE
DIRECTION OF GRAIN.

C) E M EXAMPLE:
GIVEN: P, AN ALLOWABLE BOLT LOAD PARALLEL TO
/ GRAIN =6,000 POUNDS, 0, AN ALLOWABLE LOAD
J PERPENDICULAR TO GRAIN = 2,000 POUNDS.
,, /REQUIRED: N, AN ALLOWABLE LOAD AT AN ANGLE
/"" OF 40 *TO GRAIN.
/ SOLUTION: CONNECT WITH A STRAIGHT LINE 6,00O
POULN/S ON OX(a) WIVTH THE INTERSECTION ON OYKb) OF A
// /VERTICAL LINE THROUGH Z7OOO POUNDS. THE POINT WHERE
/ THIS LINE (ab) INTERSECTS THE LINE REPRESENTING
S"" \THE GIVEN ANGLE 40, IS DIRECTLY ABOVE THE
.... t-lLLOkW,-.: BOLT LOAD, 3285 POUNDS.
...... / yFTHE CHART IS A GRAPHICAL SOLUTION
y/ / ^ | .,^^ ~OF THE HANKINSON FORMULA:
N P r/N + ,Q Cos- z












1,000 2,000 3,000 4,000 5,000 6,000 7,000 9,000 9,000 .. "3.
ALLOWABLE LOAD OR STRESS FOR P, 0, & N


SCHOLTEN NOMOGRAPH FOR DETERMINING BEARING STRENGTH OF WOOD AT VARIOUS ANGLES TO THE GRAIN
(REPRODUCED BY PERMISSION OF THE FOREST PRODUCTS LABORATORY)


Z V 34670 F












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