38 



INFLUENCE DIAGEAMS 



The criterion for the position of wheel loads which 

 produce maximum stresses is found as follows: 



-TF 2 (-tan 3 '+tan 2 )+TfY(tan 3 '-tan 2 ) 



+ TF 3 tan0 3 '=0, (66) 



or 



TF(tan 3 ') =(W 2 + W 2 ') tan 2 . . . . (67) 

 Substituting the values of the tangents, 



f 



7T (68) 



In case the chords are parallel, then hi = h 2 and ss'=d' 

 and the criterion becomes the same as developed for Fig. 4. 



Upper Segment of Vertical in the " K " Truss. In Fig. 28 

 a section cutting the upper segment of the vertical t/ 3 Z/3 



FIG. 28. 



also cuts the members UzU, M 2 L 3 , and Z/2L 3 . Taking 

 the center of moments at the intersection of the chord 

 members UsU* and L 2 L S , the moment influence diagram 



