CONTINUOUS TRUSSES 53 



The influence diagram for - - is indicated by the heavy 



s 



lines in Fig. 35. This is the base diagram with CD = unity. 

 The ordinates represented by the expression - are 



laid off above the line DB. The influence diagram for 



- is the shaded area DEGFB. For any other diagonal 



s 



the lines DE and EF, only are changed. 



The position of wheel loads producing the maximum 

 moment is found by trial. This is easily done as the 

 influence areas are nearly triangular in form. 



For loads in the third span, 



M L =Q, M R =- 

 and 



= TF 



4+6n 



The influence diagram is indicated by the shaded area BKM . 



As before, the position of wheel loads is found by trial. 



Continuous Truss of Two Equal Spans. If there is no short 

 span over the turntable n=0 and the only changes in the 

 influence diagrams given above will be the ordinates to 

 the polygonal figures. These will be increased in the 

 ratio of 4+6nto 4. 



