TAHU-: \. 



Breaking weight of Beam LX = 16,050 Ibs. 

 " " " LXt = 18,400 " 



COMPRESSIVE STRENGTH. 



The experiments to determine the coinpressive strength of the 

 various timbers have been chiefly made with columns cut out of the 

 sticks already tcs ted transversely. These columns were, in the first 

 place, carefully examined to see that they had suffered no injury. The 

 following inferences may be drawn : 



(1) The compressivc strength of Douglas Fir and of other soft 

 timbers is much less near the heart than at a distance from the heart. 

 Attention may be directed to the rase of three equal specimens A, B 

 and C (see photograph page 19), cut out of Beam XIII. The com- 

 pressivc strength of C was found to be 7,706 Ibs. per square inch as 

 compared with 6,G53 Ibs. per square inch, the compressive strength of 

 A. The difference of strength is undoubtedly due to the very much 

 larger proportion of soft to hard fibre, or of summer to spring growth 

 in C, as compared with the proportion in the case of A. The compres- 

 sive strength of the timber increases with the density of the annular 

 rings. 



(2) When knots are present in a timber column, the column will 

 almost invariably fail at a knot or in consequence of the proximity of a 

 knot. 



(3) Any imperfection, as, for example, a small hole made by an 

 ordinary caut hook, tends to introduce incipient bending, or crippling. 



(4) When the failures of average specimens commence by an initial 

 bonding, the compressivr strengths of columns of about 10 to 25 

 diameters in length agree very well with the results obtained 'by Gor- 

 don's formula, the co-efficients of direct compressive strength per square 

 inch being 6000 Ibs. for Douglas Fir and 5000 Ibs. for White Pine. 



Gordon's formula, however, is not at all applicable in the case of 

 specially good or bad specimens. It is often found that a very clear, 

 sound specimen, of even more than 20 diameters in length, will show no 

 signs of bending, but will suddenly fail by crippling under a load as great 

 as that sufficient to crush a shorter specimen. 



57 



