TASMANIAN TIMBERS. 61 



TRANSVERSE STRENGTH, DEFLECTION, AND 



ELASTICITY. 



(A. O. Green.) 



Experiments made in Hohart in May, June, and July, 1902. 



Size of specimens 30 x 1 x 1 inches, of Tasmanian 

 timbers of the ordinary quality accepted by the Tasmanian 

 Government Railway Department for maintenance pur- 

 poses — the Deal and Oregon the best that could be got. 

 The time of each experiment was about an hour. About 

 three-fourths of the load was put on slowly, with thirty- 

 pound lead-weights; then fourteen pounds, then lighter 

 weights, until the breaking load was attained ; all at about 

 the rate of thirty pounds in five minutes. 



The specimens were supported on fixed wooden supports 

 of tvv^o feet clear span, and the weights were placed in a 

 scale-pan hung on the centre of the specimen by a half-inch 

 shackle. The specimens weighed from half to about a pound 

 each, but this weight is neglected in the deductions. 



In all the experiments but two the sap-side was dow^n and 

 the heart up. The deflection was taken by means of a 

 scale divided to fiftieths of an inch, standing on the specimen 

 and against a fixed board, with a vernier, bridging the span. 



In the accompanying table the symbols used in the 

 formulae are as follows : — W = weight in pounds, L = 

 length in inches, b = breadth in inches, d = lepth in 

 inches, § = deflection in inches, / = length in feet. S, 

 E and A are constants for transverse breaking " Strength," 

 modulus of " Elasticity," and for the stiffness of beams, the 

 deflection of which does not exceed one four-hundred-and- 

 eightieth of the span. The last, A, is Tredgold's formula 

 for the stiffness of beams, which is often quoted in tables for 



European timbers where depth in inches, d = / ^ ^ and 



c = -p:rT- . S ^ the breakinef-weieht of a beam 1 foot 



X 1 inch X 1 inch, supported at the ends and loaded in the 

 centre. 



