THE STRESSES IN A STEEL WATER-TOWER. 133 



Horizontal Stresses at the Base of the Tower. The 



amount of the horizontal thrust at the foot of each post has 

 been determined. This thrust may be resisted by direct shear 



/o 

 FIG. 33 . 



on the anchor-bolts, or by the friction of the shoe on tne 

 masonry, or by both. When thus resisted the thrust produces 

 an overturning moment on the foundation (Fig. 33). 



Or ties may be used between adjacent posts. Then the stress 



TT 



in each tie is -- sec ,3, and there is no overturning moment on 

 the foundation. 



WIND STRESSES. 



The intensity of wind pressure depends on the area of the 

 surface exposed and the velocity of the wind. The relation be- 

 tween these two quantities is not known, but in general it can 

 be said that the larger the area the less the intensity, and the 

 greater the velocity the greater the intensity. The action of a 

 wind current is probably analogous to the action of a stream 

 of water. Obstructions produce cross-currents and eddies, 

 making the pressure on a given unit area of the exposed surface 

 variable. The shape of the exposed surface doubtless in- 

 fluences the intensity. Water-towers are usually placed in 

 exposed positions. Their importance makes it advisable that 

 they be designed to withstand the greatest wind pressure that is 



