112 BELL SYSTEM TECHNICAL JOURNAL 



Therefore, under the conditions assumed, and only under such conditions, 

 we may say that the loads per pin (P) comparable to the assumed concen- 

 trated loads (W) would be 



I lOA arms — roofed 

 P = 0.4W for < lOA arms— beveled 

 [lOB arms — roofed 

 and 

 P = 0.364W for lOB arms— beveled 



While these results are restricted to the four arm types listed, the same 

 principles followed in arriving at these results may be applied to other types 

 and sizes of arms, and to other conditions of loading. Whether the conver- 

 sion of single concentrated loads to loads per pin is performed by the method 

 illustrated in Calculations 1 and 2 of the appendix, or is done by a moment 

 diagram, as in Fig. 2, the procedure recommended is as follows: 

 Step 1. Determine the critical section under the concentrated load. 

 Step 2. Divide the bending moment at the critical section by the total-per- 

 pin lever arm to the critical section to determine the load per pin. 

 Step 3. Check the tiber stress (under such loads per pin) at various sections 

 to see whether the location of the critical section differs under load 

 per pin. 

 Step 4. If it does differ, proceed as shown for the beveled lOB arm (viz., 

 the comparable load per pin is equal to the resisting moment of 

 the critical section divided by the total-per-pin lever arm to the 

 critical section). If it does not differ, the load per pin as deter- 

 mined in Step 2 is the comparable load per pin sought. 



Conclusions 



(1) The location of the critical section under loads distributed at each 

 pin position must be determined before undertaking the conversion of 

 concentrated loads to distributed loads. 



(2) The location of the critical section of a crossarm under a given condi- 

 tion of loading may or may not be the same under a different condition of 

 loading. 



(3) The load per pin comparable with a given concentrated load is equal 

 to the resisting moment of the critical section divided by the total-per-pin 

 lever arm to the critical section. 



(4) While the results shown are confined to the conversion of concentrated 

 vertical loads to distributed loads for lOA and lOB arms only, the principles 

 of the study may be applied to other types and sizes of arms and to other 

 conditions of loading. 



