Resistance To Crushing Across The Fibres

When a vertical piece of timber stands upon a horizontal piece, the latter is compressed at right angles to the length of the fibres, and in this position it will not withstand so great a compressive force per square inch as does the vertical piece, whose fibres are compressed in the direction of their length.

Not many experiments have been made on this point.

Tredgold found that Memel fir was distinctly indented with a pressure of 1000 lbs. per square inch, and English oak with 1400 lbs. per square inch.

Mr. Hatfield's experiments chiefly on American woods, are quoted in Hurst's Tredgold, and form the basis of a table in Hurst's Pocket-Book, from which the following are taken : -

Force per sq. inch required to crush the fibres transversely

1/20 inch deep.

Fir, spruce .....

•22 tons.

Pine, Northern Memel ....

•60 „

„ White (P. strobus) American

•27 „

Mahogany, Honduras

•58 „

„ St. Domingo ....

192 „

Oak, English .....

•90 „

„ American .....

.84 „

Ash, American .....

1.03 ,,

Chestnut .

•42 „

Resistance To Shearing

On this point also but few experiments have been made.

The resistance to shearing in direction of the fibres of the wood is of course much less than that across the fibres.

Wood.

Resistance to Shearing per sq. inch in lbs.

Along Fibres.

Across Fibres.

Fir...

556 to 6341

Oak ....

2300 2

40002

American oak..

780 3

Ash and elm...

1400 2

Spruce...

600 2

Red pine ....

500 to 800 2

1 Barlow On Strength of Materials, p. 23. 2 Rankine's Civil Engineering.

3 Hatfield, quoted in Hurst's Tredgold.