SIMPLE TRUSSES 



27 



SPECIAL CASE 



Diagonal of Simple Truss, Having Center of Moments be- 

 tween the Supports. In Fig. 18 make a section cutting 

 two chords and the diagonal UL'. The intersection of 

 the two chord members is between the supports, a condi- 

 tion which has not obtained in any of the previous examples. 

 The influence diagram for moments is constructed according 



. 



to the general rule and is shown by the shaded area in 

 Fig. 18. This diagram shows that each and every load 

 placed upon the span produces the same kind of stress 

 in the diagonal UL'. 



The criterion for the position of wheel loads which 

 produce the maximum moment is found as follows: 



dx 



3 ) +TF 2 (-tan 2 +tan 

 + TF 3 tan 3 =0, . . 



. (61) 



