THE STRESSES IN A STEEL WATER-TOWER. 



135 



The wind stresses in the tank bottom and in the circular 

 girder cannot be definitely determined. They are probably 

 small in comparison with the gravity stresses. 



Stresses in the Tower. The wind loads acting on the tower 

 are the loads transmitted to it by the tank and the direct wind 

 pressure on the members of the tower. The former are applied 

 at the tops of the posts, and the latter will be considered as con- 

 centrated at the panel points. 



Consider the tank a rigid body, then the reactions at the 

 top of the posts due to the wind pressure on the tank will be a 



FIG. 34. 



set of horizontal forces and a set of vertical forces. Let P be 

 the total wind pressure on the tank, including the roof. 



This may be considered as acting at the center of gravity of 

 the projected area. (The center of pressure on the conical bot- 

 tom is at J the depth, and on the hemispherical bottom at a depth 



of . The pagoda roof may be reduced to an approximately 



3 71 " 



equivalent cone for the purpose of this computation.) Let G 

 be the distance in feet from the tops of the posts to the centre of 

 gravity, then the overturning moment in foot-pounds is 



M = PG. 



This overturning moment must be resisted by the connections of 

 the tank to the posts. 



