INFLUENCE DIAGRAMS 



Dividing through by 5x and placing *=0, 



oX 



= (W 2 + W a ' + W 3 ) ( - tan e a ) + (W 2 + W 2 ') (tan 2 ) = 



(13) 



(14) 



where W = W 2 + W 2 ' + W 3 = the total load on the span. 

 Therefore, from equation (14), the desired criterion is 



where 



W 2 +W 2 ' 

 -- 



1 s+b d . s 



=' or d =- s 



The value of d r is found graphically from the influence 

 diagram by drawing a line through D parallel to CB until 

 it cuts the vertical line through F, then d' is the distance 

 indicated in the figure (Fig. 1 and those which follow). 

 This value may also be found graphically without drawing 

 the influence diagram by simply drawing in the truss dia- 

 gram the line Mm parallel to the bottom cut chord LU and 

 prolonging it until it cuts a diagonal line drawn from the 

 intersection of the cut top chord and a vertical through the 

 left end of the cut stringer to the intersection of the cut 

 bottom chord and the vertical through the right end of 

 the cut stringer. This point is indicated by the letter m in 

 the figure. The horizontal distance of this point m from 



