TESTS OF ROCKY MOUNTAIN WOODS FOE TELEPHONE POLES. 11 



There seemed to be no consistent difference in the behavior of 

 straight and spiral grain poles. 



The typical failure of the western red cedar poles was a splinter- 

 ing tension about 2 feet from the load point. The wood separated 

 easily along the annual rings, and the splinters were long and numer- 

 ous. Probably due to this quality, as weU as to the depth of checks, 

 three poles failed in longitudinal shear, and in two others shear 

 occurred after the maximum load had been passed. 



In the air-seasoned lodgepole pine poles there were 18 tension 

 failures and 4 failures from longitudinal shear. Of the 18 tension 

 failures, 9 were of the splintering type characteristic of the cedar 

 poles and 9 were simple tension failures ; that is, without the exhibi- 

 tion of brittleness or unusual splintering. 



The typical failure in fire-kiUed lodgepole pine was a simple ten- 

 sion close to the load point. The wood often had a rather brash 

 appearance, and, except for two poles, did not splinter to any extent. 

 One pole was brittle, failing near the center, and one failed by longi- 

 tudinal shear after the maximum load had been passed. 



In general the fire-killed Engehnann spruce poles failed in the 

 same manner as the fire-killed lodgepole pine. Two poles had brittle 

 tension failures, and there were no longitudinal shear failures. 



The fact that 9 of the 42 air-seasoned and only 1 of the 40 fire- 

 killed poles failed by longitudinal shear might seem at first to indi- 

 cate that the checking of the poles cut from green timber is deeper 

 than that occurring in the more slowly drying fire-killed poles. The 

 fact, however, that the average shearing stress of the cedar proved 

 to be about 15 per cent lower than that of the other species, and fur- 

 ther that the moduU of rupture in bending of both green-cut shipments 

 were higher than those obtained in both fire-killed shipments, shows 

 that there was a greater chance for shear failures in the air-seasoned 

 material than m the fire-kiUed, aside from any difference in the 

 manner of checking. 



Compression of the upper fibers, as shown by wrinkles on the top 

 of the pole, occurred some time before the maximum load was reached. 

 There was usually a noticeable increase in the bend of the load- 

 deflection curve after compression became visible. 



