DOUBLE INTERSECTION TRUSSES 



31 



load between L 2 and L 3 the influence line is a straight 

 line connecting e and e'. In a like manner the other 

 panel points are considered and the final influence diagram, 

 shown by the shaded area, obtained. The loads at LI 

 and Lii are assumed to be equally divided between the 

 two trusses and hence the influence line passes midway 

 between the two influence diagrams for these points. 



*'- >!--. -d-'-.-sj 



s >{*- id >i 



FIG. 20. 



The position of wheel loads producing maximum 

 moment is best found by trial. A criterion car be deduced 

 but it is too complicated for practical use. 



Vertical of Whipple Truss. The vertical U^L* is a 

 member of the truss shown by the full lines, Fig. 21. The 

 influence diagram for vertical shear in the panel cut is 

 DEFBD. For loads at panel points L 2 , Z/ 4 , LG, etc., the 

 ordinates of this influence diagram are correct for unit 

 loads. The loads at L 3 , L 5 , Z/?, etc., are supported entirely 

 by the truss shown by dotted lines and hence do not con- 

 tribute any shear in the panel being considered, of the 



