STRENGTH AND TESTING OF TIMBER 313 



The results of compression tests are less variable than 

 any other tests. 



So far as the engineer or architect is concerned, the 

 tests which chiefly concern them are those for transverse, 

 shearing, and crushing strength, since, long before the 

 timber would give way in tensile strain, the bolts or con- 

 nections would shear through the ends of the timber ; and 

 it may here be stated that no bolts should be nearer than 

 3 or 4 inches from the end of a timber having to bear 

 tensile stress. Moreover, the tensile and transverse 

 strength of timbers do not vary much. Mr. Julius found 

 that with the Australian timber the tensile stress was about 

 5 per cent, above the ultimate strength in cross breaking ; 

 whilst in the case of Quebec pine beams tested by Mr. 

 H. D. Smith, M.I.C.E., the ratio of transverse to tensile 

 strength only varied between 0'82 and 1*31 in the same beam. 



In tensile tests on timber the experiments have generally 

 been made upon small turned specimens of about 1 inch 

 in diameter ; the centre portion of a piece of timber for 

 about 6 inches long is turned down to a diameter of about 

 1 inch, the thicker portions at the ends being secured 

 in the grips of the testing machine ; there is difficulty, 

 however, in holding them, and occasionally the enlarged 

 ends draw through the grips, and the timber fails by 

 shearing along the grain, and not in tension. 



Timber is not a satisfactory material for a tie bar ; the 

 only case in which it is likely to be used in tension is in 

 the tie beam of a roof where the strain it has to bear is 

 generally small. 



In making calculations for the strength of beams or 

 columns it is advisable to assume either the minimum results 

 of tests, or thereabouts, as it is safe to assume that there 

 would be no more care exercised in the selection of timber 

 for actual work than there would be in the case of timber 



