814 TIMBER 



for testing, probably not so much. One hundred tests on 

 " yellow pine " (pitch pine) beams 3 inches by 10 inches to 

 about 4^ inches by 12| inches, and one piece 6 inches by 

 16 inches, made by Lanza, gave an average modulus of 

 rupture of 7,442 Ibs. ; yet he says " I should not feel justified 

 in using a greater number than 5,000 Ibs. per square inch," 

 although only nine of the samples tested fell below that 

 limit. 1 Laslett, on the basis of small pieces of the same 

 timber, gave the minimum modulus of rupture as 10,044 Ibs. 

 per square inch, Hatfield as 9,000 Ibs. per square inch, and 

 Eodman 8,796 Ibs. per square inch, proving what we have 

 said about the mistake of trusting the results of tests made 

 on small and perfect samples of timber. 



Again, for spruce beams tested by Lanza the average 

 modulus of rupture in 161 tests on pieces from 2 inches by 

 7 inches to 7 inches by 12 inches was 4,521 Ibs. per square 

 inch, yet he says that although only seven of the tests fell 

 below 3,000 Ibs., that is all that could with safety be used, 

 though if timber were specially selected he might allow 

 4,000 Ibs. For similar timber Eankine gives 9,900, Hatfield 

 7,506, Laslett 7,508, and Trautwine recommends 5,400 Ibs. 

 per square inch. 



Mr. H. D. Smith, M.I.C.E., tested to destruction a number 

 of Quebec yellow pine beams, 9 inches by 9 inches, 18 inches 

 by 9 inches, and 12 inches by 12 inches, with a span of 14 ft., 

 and the mean transverse strength was found to be 3,807 Ibs. 

 per square inch. On beams of the same timber, tested under 

 similar conditions and at the same place in 1875 by Mr. 

 C. Graham Smith, the mean transverse strength was 4,491 Ibs. 

 per square inch for a scantling of 14 inches by 15 inches, 

 with a clear span of 10 ft. 6 inches. 2 For this same class of 



1 ." Applied Mechanics," G. Lanz;i, 1899. 



2 Min. of 1'roc. Inst. <_'.E., Vol. C'XXYllL, and Eiiyineeriiiy, 

 May 7th, 1875. 



