310 FARM BUILDINGS IN SOUTH AFRICA 



from the centre of the tension rods to the tension surface of the concrete, then 

 the thickness of the tank wall at the bottom 



= 5-3 + 1-75 



= 7 inches approximately. 



We next proceed to calculate the horizontal reinforcement. 



The total pull in the steel —ft . a 

 but total pull in steel = total thrust in concrete, 



but from IT., 



i.e. the cross-sectional area of horizontal reinforcement in 1 foot height of the 

 wall at the bottom = 0'317 sq. in. 



Let us try ^" dia. round bars. The cross-sectional area of a half-inch bar 

 = 0"1963 sq. in., and we require to provide a cross-sectional area of 0*317 

 sq. in. to the foot of height, therefore 0*1963 sq. inch is sufficient for — 



,_ 0-1963 n lA . , 

 12 X . 317 = 7-44 inches, 



or say 7^ inches. Therefore horizontal y dia. rods, at the bottom of the wall, 

 should be spaced 7£" apart vertically from centre to centre. 



312*5 



Calculating similarly for a value of iv = 2 lbs. per sq. ft., we find that 



the thickness of the wall at mid-height, i.e. 2£ feet above the bottom of the 

 tank, = 5i". 



If the faces of the wall be straight this will make the thickness of the wall 

 at the top = 4 inches. 



The spacing of the half-inch diameter horizontal rods, at mid-height of the 

 wall, works out to 10£ inches; therefore • the 9^-inch spacing shown in the 

 drawings will be quite safe. 



The piers are next calculated. Each pier is assumed to take the pressure of 

 water on a surface extending 4 feet on each side of it (the piers being 8 feet 

 apart). The area of this surface for 5 feet depth of water = 8 X 5 = 40 sq. ft. 



The pressure per square foot at the bottom of the tank = 312'5 lbs., therefore 



