32 



INFLUENCE DIAGRAMS 



truss shown by the full lines. Therefore, the ordinates 

 in the influence diagram directly below these points are 

 zero. Connecting these points with the ends of the ordinates 

 which are correct, as shown in Fig. 21, the influence diagram 

 shown by the shaded area is obtained, The loads LI 

 and Z/ii are assumed to be equally divided between the 

 two trusses. 



FIG. 21. 



Diagonal of Whipple Truss. The diagonal U 2 L^ Fig. 

 22 is a member of the truss shown by full lines and its 

 influence diagram is constructed in a manner similar to 

 that explained for the vertical UL. The influence diagram 

 is shown by the shaded areas. 



The position of wheel loads producing the maximum 

 vertical shear is found by trial. 



Top Chord of Sub-divided Double Triangular Truss. The 

 two principal trusses are shown in Fig. 23 by full and 

 dotted lines. The top chord member U&U& forms a part 

 of each truss. The influence diagram for UsUs as a member 

 of the truss shown by full lines is DABD and that for the 

 truss shown by dotted lines is D'A'B'. Connecting these 





