RELATIVE BEXDIXG STRENGTH OF CROSSAR.US 



39 



include a new type ("W6") with 16 i)in positions. It was felt that, if the 

 additional pin holes in the type W6 did not unduly weaken the arm, it could 

 not only replace the old t^-pe "JW" arm with 8 pin positions but also be used 

 in installations where greater flexibility in wire spacings might be required. 



10 20 30 40 50 60 



distance: from center of arm -inches 



Fig. 8 — Resisting moments and maximum bending moments for clear JW and W6 



crossarms. 



In order to obtain an estimate of the strength relationship between the two 

 types, strength tests were made of 10 matched arms of each type. The test 

 arms were made of air-seasoned, clear Douglas fir. The dimensions of the 

 crossarm blanks were 3J" x 4|" x 20'. In selecting the 10 blanks from 

 which the test arms were made, only straight grained pieces free from 



