REINFORCED CONCRETE TANK 309 



Therefore, equating II. and III. — 



/« ®i= A. 



ft E c d-Ji 



16,000 rf — A 



h _15 

 rf — A - 32 

 32A = 15^—1 hh 



h=W (IV.) 



We will design for a bending moment, M, for a continuous beam, of y~- 



where 



/ — the distance between the piers = 8 feet, 



w = the water pressure in lbs. per sq. ft. at the bottom of the tank, supposing 

 the tank to be rilled to the full depth of 5 feet, = 62-5 X 5 = 312-5 lbs. 

 per sq. ft. We consider this pressure to act over a horizontal strip, 

 1 foot high, at the bottom of the wall, then — 



wP 312-5 X 8 X 8 , . „ 



M = To = io fooWbB ' 



M 312-5 X 8 X 8 X 12 . . „ 

 •M- = Yo mch-lbs. 



M = 24,000 inch-lbs. 



Now M = the moment of resistance of the section, therefore, 



referring to Fig. 216 — 



u= (i xt& X a -i) • <w 



»-(r xl *XH) 



since b = 12 inches. 



M = 300(Wd — ^\ 



M = 3000hd — 1000A2. 



Substituting for h from IV. we have — 



M = (3000 X W}d* — 1000(|f)2rf2 

 M = 957-4^2 _ioi-9cP 

 M = 855-5rf 2 

 d2 _ 24,000 

 855-5 

 hence d — 5*3 inches. 



Allowing a depth of rmbedinent of the steel in the concrete of 1| inches 



