140 



TOWERS AND TANKS FOR WATER-WORKS. 



(Do not confuse <, the inclination of the posts, and p, the inclina- 

 tions of the sides.) 



Each foundation is common to two trusses, and the loads 

 from the two must be combined algebraically. And in addition 

 to these there is the direct load resulting from the vertical load 

 at the top of the post. 



The total vertical load due to wind pressure on any founda- 

 tion, as at A, is the sum of the vertical component of the direct 



stress in the post, the vertical com- 

 ponent of the reaction U of the 

 truss AB, and the vertical compo- 

 nent of the reaction U l of the truss 

 AF, due attention being given to 

 the signs. 



The horizontal load due to wind 

 pressure (Fig. 38) on any founda- 

 tion, as at A, is the resultant of the 

 horizontal component (radial) of the 

 direct stress in the post (a), the 

 horizontal shear from the truss A B 

 (b), the horizontal shear from the 

 truss AF (c), the horizontal com- 

 ponent of the reaction U of the truss AB (d), and the hori- 

 zontal component of the reaction U l of the truss AF (e). If 

 the bottoms of the posts are connected by struts (ties), the 

 resultant horizontal load on each foundation equals s (Fig. 36), 

 and its line of action is parallel to the direction of the wind. 



CONCLUSION. 



The possible conditions of loading for a water-tower are: 



1. Weight of structure. 



2. Weight of structure and weight of water. 



3. Weight of structure and wind pressure. 



FIG. 38. 



