316 TIMBER 



stiffer than one, doubtless owing to the friction between the 

 surfaces. 



Bolts increase the friction and produce a marked effect 

 on the stiffness of beams, although, with bolted beams as 

 with unbolted, the upper beam slides over the one below it. 



In the case of flitch beams, that is, whole or cut timbers 

 laid side by side and bolted together, tests show that the 

 main difference between these and simple beams of the 

 same scantling is that they break more suddenly. 



Loads placed upon timber columns, as upon columns of 

 other material, should be in the centre, as all tests show 

 that columns eccentrically loaded give considerable reduc- 

 tions in strength, and Lanza found this particularly 

 noticeable in the case of oak columns. 1 



The question of compression at right angles to the grain 

 and the shearing strength of timber has not as yet been so 

 carefully studied as that for transverse strength and com- 

 pression parallel to grain. 



Pine and spruce will only bear about one-seventh, hickory, 

 oak, ash, and some of the Australian hardwoods about 

 one-half to one-fourth, of the load at right angles to 

 the grain which they will bear parallel to the grain 

 so that, in the case of timber columns carrying heavy loads 

 and having these loads transmitted to timber base plates 

 or caps, proper precautions must be taken that the load on 

 the side timber is not excessive. 



Judging by a large number of tests on different timbers 

 it may be stated generally (although a few samples on 

 p. 310 show the contrary) that the strength in cross com- 

 pression is higher than in shearing, and in some of the harder 

 timbers considerably higher (see tests, pp. 120 and 219). 



1 "Applied Mechanics," G. Lanza, and " The Practical Column under 

 Centre and Eccentric Loads," by J. M. Monerieff, M. Am. Soc. C.E., 

 American Society of Civil Engineers, Vol. XLV., 1901. 



