TESTS OF ROCKY MOUNTAIN WOODS FOE TELEPHONE POLES. 9 



point of failure. The values for the amount of summerwood were 

 obtained on a 2-inch length taken from an average portion of the 

 section. Sketches were made of the manner of failure, principal 

 defects, and any characteristics peculiar to the poles tested. 



METHOD OF COMPUTING RESULTS. 



The deflections and loads at elastic limit were taken from the load- 

 deformation curves, a sample of which is shown in figure 5. To re- 

 duce the load recorded on the scale beam to the true load on the pole, 



23 

 all recorded values were multipled by ^5X2, and appear in the tables 



in the corrected form. Stresses at elastic limit and maximum load 

 were calculated for the outer fiber under the load point. The moment 

 of three-fourths of the weight of the pole was added to the moment 

 produced by the load. The comparative stiffness is expressed by 



P 



the relation j^, when P is the load at elastic limit and I and d, re- 

 spectively, the moment of inertia and the deflection at elastic limit 

 measured at the load point. 



The modulus of elastic resilience was obtained from the formula 

 one-half Vd -^ volume. In obtaining the volumes there was found 

 to be considerable difference in the shape of the poles. The spruce 

 and pine were practically of even taper, and the volumes obtained 

 by regarding the whole pole as one frustum of a cone (from top to 

 butt diameter), or as two frustums (from top to center and center 

 to butt), were practically the same. In the cedar, however, it was 

 found necessary, on account of the flared butts, to use a three- 

 frustum method (from top to center, from center to load point, and 

 from load point to butt). There was about 10 per cent difference 

 between results from the one and the three frustum methods with this 

 species. In calculating the dry weight per cubic foot, a total shrink- 

 age of 12 per cent for the fire-killed pine and spruce was assumed, and 

 10 per cent for the cedar. The air-seasoned pine poles were con- 

 sidered as being one-third below the fiber saturation point (that is, 

 a 4 per cent shrinkage in volume was assumed as having already oc- 

 curred), and the others were assumed as being half-way between the 

 dry and the fiber-saturated states. 



RESULTS OF TESTS. 



CHARACTER OF FAILURES. 



Figure 6 shows the common types of failures occurring in the poles 

 tested. 



The bend of the pole while under load was at a maximum near 

 the center of the span for the first part of the test and about 2 feet 

 nearer the load point at maximum load. This shifting at the point 

 22740°— 14 2 



