Art. 54. STRESSES IN A ROOF TRUSS FOR WIND LOAD. 73 



this method, in the truss diagram the spaces between the forces 

 (both external and internal) are lettered and a force or stress 

 is designated by the two letters adjacent to it. This causes 

 the letters in the force or stress diagram to come at the inter- 

 sections, so that a stress is represented by a line with letters 

 at its ends. This method is used only for graphic stress deter- 

 minations. Bow's notation will be used for the graphic solu- 

 tion in the following article. 



54. Stresses in a Roof Truss for Wind Load. Fig. 51 



shows a roof truss with a normal wind load on one side of the 

 roof. It is assumed that the support at E is on rollers or is free 



Stress Diagram 



Fig. 51. 



to slide without friction. Therefore, the reaction R 2 will be 

 vertical. 



When there are so many different inclinations of members 

 and external forces, the reactions as well as the stresses are 

 best obtained graphically. 



When the loads are symmetrical as in this case, their re- 

 sultant may be located immediately, and if the intersection of 

 this resultant and R 2 comes within the limits of the drawing 

 and is not too acute, the reactions may be determined, by the 

 force triangle AEFA as in Figs. 23 and 39. If the intersection 

 of the resultant and R 2 cannot be used, the reactions may be 

 determined by passing a string polygon through the only known 

 point in R^ as shown by the dotted lines. The closing line 3 



