220 



PRACTICAL STRUCTURAL DESIGN 



tions. The load line is then set off for the reciprocal diagram 

 and the reactions are scaled off on it. In this case the load line 

 must show all the loads and must be complete whereas in 

 trusses symmetrically loaded it is necessary, to draw only one- 

 half the reciprocal diagram. 

 In Fig. 136 the treatment of a Warren truss loaded on the top 



V V 



cR, 



Fig. 136. Warren Deck Truss. 



chord is given. The vertical dotted lines at the ends are in 

 compression and deliver their loads direct to the abutments. 

 The horizontal line to the first joint in the upper chord delivers 

 part of its load as a reaction, to the upper joint and part to the 

 vertical post. 



Notice carefully the treatment of the Warren through truss 

 (loaded on lower chord), as shown in Fig. 137. 



In Fig. 138 is shown the reciprocal diagram for a Howe truss 

 loaded on the lower chord and in Fig. 139 is shown a Howe truss 



rR, 



n/V V 



\ 



Fig. 137. Warren Through Truss. 



loaded on the upper chord. In the through truss the middle 

 vertical carries a load, but in the deck truss it carries no load, as 

 shown by the two letters at the end of the reciprocal diagram. 

 All reciprocal diagrams must close and when a line must be 

 omitted in order to make a diagram close, put the extra letters 

 at the joint where there is an apparent jumble and letter the next 



