TESTS OF ROCKY MOUNTAIN WOODS FOR TELEPHONE POLES. 17 



A comparison based on the fiber stress developed is equivalent 

 to one based on uniform ground-line diameter. In practice, however, 

 it is customary to specify top diameters. On a basis of measured 

 tapers and the fiber stresses found by test, the loads may be calcu- 

 lated for all shipments, using a uniform top diameter of 7 inches. 

 Table 4 gives the calculated loads for such a comparison. The tapers 

 used in the calculations were, for western red cedar, 0.098 inch per 

 foot length; for the air-seasoned lodgepole pine, 0.077; for fire-killed 

 lodgepole pine, 0.096; and for fire-killed Engelmann spruce, 0.130. 

 These tapers do not include the flare of the butt. The length from 

 top to the load point was taken as 19.5 in all cases. Since the strength 

 of a pole varies as the cube of its diameter, it is evident that differ- 

 ences in taper wiU materially affect the strength. On a basis of equal 

 top diameters it will be seen from Table 4 that — 



1. There is practically no difference in strength between air- 

 seasoned lodgepole pine and western red cedar. In stiffness the 

 lodgepole pine poles exceeded the cedar by about 25 per cent. 



2. The fire-killed poles, both lodgepole pine and Engelmann spruce, 

 were practically equal to the cedar in strength at elastic limit and 

 about 20 per cent below it at the maximum load. 



Table 4. — Strength of poles compared on a basis of 7-inch tops. 





Seasoning condition. 



Load at elastic 

 limit. 



Maximum load. 



Species. 



Average. 



Ratio to 



red 



cedar. 



Average. 



Ratio to 



red 



cedar. 



V/estern red cedar 



Cut green and air seasoned 



Pounds. 

 7,800 

 8,000 



Per cent. 



100 



103 



96 



96 



Pounds. 



12, 000 



11,620 



9,500 



9,400 



Per cent. 

 100 





97 



Do 



Fire killed 10 years 



...do 



7,470 

 7,500 



79 





78 









SMALL, CLEAR PIECES CUT FROM POLES. 



Table 5 gives the results of tests on small, clear pieces in bending, 

 compression parallel to grain, compression perpendicular to grain, 

 and shearing. For each pole the average strength values for all 

 pieces taken from it are given, and at the bottom of the tables are 

 the averages of all minor tests for the species. 



Table 6 gives the average strength values of minor tests sum- 

 marized by species and condition of seasoning. An examination 

 of the average results shows in general very comparable values for 

 the fire-kiUed pine and spruce and for the cedar. The cedar, how- 

 ever, falls about 16 per cent below the pine in shearing strength and 

 the spruce about 12 per cent below it in crushing strength. The 

 lodgepole pine from Montana showed a bending strength nearly 40 



