36 



INFLUENCE DIAGKAMS 



a series of the letter K. Making a section cutting U 2 Uz, 

 UzMz, MoL/z and L 2 L 3 , it at once appears that the upper 

 and lower chord members in a panel have equal horizontal 

 components since the centers of moments are in the same 

 vertical line. 



The construction of the influence diagram for moments 



1-2 L 



FIG. 26. 



follows the general rule. The criterion for wheel loads 

 which provide the maximum moment is 





(65) 



where W is the total load on the span and Wi the total 

 load between the left support of the truss and the center 

 of moments of the chords considered. 



Diagonal Web Members of the " K " Truss. The usual 

 method of sections cannot be employed as any section 

 made through the truss cuts at least four members. From 

 the arrangement of the diagonals it is clear that the pair 

 in one panel must have horizontal components equal in 





