18 



INFLUENCE DIAGRAMS 



of LL". The graphical determination of d' and x r is evident 

 from the truss diagram. 



The criterion for wheel loads producing maximum 

 moment is 



. 



(47) 



If the chords are parallel the criterion becomes 



W 



d 



(48) 



Vertical of Sub-strut Truss. As indicated in Fig. 10, the 

 vertical of a sub-strut truss is a member of the main truss. 



FIG. 10. 



The auxiliary truss acts simply as a trussed stringer. The 

 construction of the influence diagram follows the general 

 rule using the horizontal projection of LL" as the length 



