CHAPTER XIII 



STRENGTH AND TESTING OF TIMBER 



Varying Results obtained in Testing Timber and Causes thereof Tests 

 ou American and Australian Timber Necessity for Tests on 

 Large Pieces of Timber Comparison of Strengths of Timber, 

 Green and Dry Great Increase of Strength in Timber caused by 

 Drying Tables of Strengths of Timber with Varying Degrees of 

 Moisture Effects of Kiln Drying Long Time Tests on Beams 

 Various Methods of Testing Tests by Lanza, H. D. Smith, 

 C. Graham Smith, Major Bock, and others Strengths of Timber 

 in Side Compression and Shearing Weight of Timber Variable 

 Weight Compared with Number of Rings per Inch Factors of 

 Safety. 



THE results obtained when testing timber vary very 

 much more than those obtained with iron or steel. Of all 

 structural material timber is the most variable in strength, 

 two pieces from the same tree, or even the same log, often 

 producing very different results; the main reason being 

 that timber is a built-up structure and subject to internal 

 strains, and these strains vary with each piece of timber. 

 It is because of this great variation in tests that in the 

 calculation of stresses for timber structures it has been 

 usual to allow a much larger margin of safety than in the 

 case of steel structures, and probably this is why we have 

 had a singular immunity from failures in timber structures, 

 the margin of safety allowed being much greater than was 

 really necessary. 



Nearly all calculations for strength of timber, until quite 

 recent years, were based upon tests made on small specimens 

 of wood 1 or 2 inches square, and all who have had to 



