5 



STRESSES IN ROOF TRUSSES 



and to the resultant of the external loads ; where both ends of the 

 truss are equally free to move (2) the horizontal components of the 

 reactions are equal; and where one end is fixed and the other end is 

 on frictionless rollers (3) the reaction at the roller end will always 

 be vertical. Either case (i) or case (3) is commonly assumed in cal- 

 culating wind load stresses in trusses. Case (2) is the condition in a 

 portal or framed bent. The vertical components of the reactions are 

 independent of the condition of the ends. 



Wind Load Stresses: No Rollers. The stresses due to a nor- 

 mal wind load, in a Fink truss with both ends fixed to rigid walls, are 

 calculated by graphic resolution in Fig. 32. The reactions are parallel 



Wind Load 

 No Rollers 



O 200O 4OOO 6000 



FIG. 32. 



and their sum equals sum of the external loads; they are found by 

 means of force and equilibrium polygons as in Fig. 15 and Fig. 27. 



