SPECIFICA TIONS. 35 



The external pressure of the wind shall be t aken at and calcu- 

 lations made for not less than thirty (30) pounds per square 

 foot as exerted upon the vertical diametral plane of the tank 

 and exposed tower surfaces. 



The tower shall be proportioned to sustain the combined 

 load due to the weight of the water, the metal of the structure, 

 and the assumed wind pressure and resulting stresses. Where 

 the main posts connect to the tank-shell the posts shall be rein- 

 forced so that the area of section for a distance of thirty-six (36) 

 inches below shall be equal to an area one and one-half (ij) 

 times the area of the post. 



The stresses shall not exceed fourteen thousand (14,000) 

 pounds per square inch for members not exceeding ninety (90) 

 times their least radius of gyration between supports, and for 

 greater lengths the allowable unit stress shall equal twenty thousand 

 (20,000) pounds minus seventy (70) times the length in feet 

 divided by the least radius of gyration of the section in inches. 



No main post shall exceed one hundred (100) times its least 

 radius of gyration, and no other strut shall exceed one hundred 

 and fifty (150) times the radius or such length that the fibre 

 stress due to bending from its own weight shall exceed four 

 thousand (4000) pounds per square inch of metal. 



No shape weighing less than four (4) pounds per linear foot 

 shall be used except for reinforcement of parts or for ornamental 

 or unimportant features. 



Columns shall be secured to steel base plate, reinforced with 

 angle connections, and shall be designed to resist vertical shear 

 stresses not exceeding ten thousand (10,000) pounds per square 

 inch. The area or bearing value of the base plate shall be such 

 that not more than four hundred (400) pounds shall be exerted 

 upon the upper face of a monolithic capstone, transferring not 

 more than one hundred (100) pounds per square inch to a sup- 

 porting masonry pier, so proportioned that not more than 



tons per square foot shall be delivered to the subfoundations. 



