SIMPLE STRUCTURES 



203 



proceed to the load QR and determine the stress in EF by the auxiliary construc- 

 tion shown by the dotted lines in the diagram. Then determine the stress in ED 

 by the same auxiliary construction. Having found the stress in JD, we may then 

 go back to the load PQ and complete the diagram. 



Graphical analysis of 

 Howe truss 



309. Analyze graphically for both dead and wind loads the Howe roof truss 

 shown in Fig. 152 for a span of 50 ft. and of one-half pitch, that is, with a rise 

 of ^ - 12.5 ft. The trusses are spaced 16 ft. apart ; the weight of each truss may 

 be taken as 2.5 lb./ft. 2 of horizontal area, the roof covering as 10 lb./ft. 2 of roof, 

 and the snow load as 20 lb./ft. 2 of roof. The wind load, based on a pressure of 



