278 



PRACTICAL SPRUCTURAL DESIGN 



the columns, each carrying its proportionate share of the load. 

 This vertical load is not considered in the graphical stress dia- 

 gram used to determine the force due to wind, so must be added 

 to the wind forces after the stress diagram is constructed and 

 scaled. The struts and ties carry no part of the tank and water 

 load, being used to take care of the wind load and to divide the 

 column into intermediate lengths so the columns may be as 



c 5000 b 



Stress Diagram, 



, , 

 33-0 



Tower Diagram. 



Fig. 180 Stresses in Water Tower 



small as possible, each column being considered as having a length 

 equal to the height of one bay. 



The plan of the base in Fig. 180 shows that the maximum 

 stresses in the rods and struts occur when the wind is blowing 

 against the side of the tower. The maximum stresses in columns 

 occur when the wind is blowing diagonally across the tower and 

 are 0.707 of the amounts obtained from the diagram. The wind 

 force is not the result of a constant load, so in a number of specifi- 

 cations only 80 per cent of the maximum wind force is considered. 



The wind acts at the top through the center of gravity of the 

 filled tank, and at the joints on the side of the tower. In the 



