RELATIVE BEXDfXG ST RES GT II OF CROSS A RMS 



31 



vertical position; and Calculation 5, in which the knots were assumed to be 

 immediately below the top segment in a horizontal position. The results 

 of these two calculations are shown in Table 2. It has heretofore been gen- 

 erally assumed that in pinhole sections knots less than \" in diameter were 

 more damaging in a vertical position than in a horizontal position. The 

 results of Calculations 4 and 5, however, show that the horizontal knots 

 immediately below the top segment are the more damaging. In order to 

 compare the effect of knots so located with the effect of knots at the extreme 



JliM iiMti^ 



3» 



^iicURVE I FOR 3-ix44 SECTIONS^ 



I CURVE 2 FOR 3^'x 4^" SECTIONS i 



r| CURVE 3 FOR S-j^'x 4" SECTIONS | 



mn 



.5 I IS 2 



KNOT DIAMETER - INCHES 



Fig. 5 — Pinhole sections. Section modulus of crossarm sections containing knots of the 

 sizes shown on the base line and located in damaging positions. 



top of the section, the following two computations assumed \" and 2" hori- 

 zontal knots at the latter location: 



l'\ Knot at Section Top: 

 ^5 



J _ .02875 (3.09375)' 



= 1.48156 



S = 2.9631 

 2" Knot at Section Top: 



kS = 



.92875 (2.09375)- 



= .67857 



5 = 1.3571 



