12 BULLETIN 789, U. S. DEPARTMENT OF AGRICULTURE. 



In determining what reinforcing will be used for any tank for its 

 full height we can proceed in three ways to allow for the decrease 

 from bottom to top in the steel area required : 



A. Fix a imiform spacing, and use decreasing sizes of bars. 



B. Select one size bar and increase its spacing. 



C. A combination of the first and second ways. 



In any case, having determined the size and spacing of the steel at 

 the bottom, the levels at which the succeeding changes in bar sizes 

 or spacings may be made can be obtained from the chart by methods 

 the reverse of those abeady outlined. In the present example, if we 

 select 1^ by J inch bar, 9 inches on center, as the reinforcing at the 

 bottom, we can proceed as foUows : 



Follow the diagonal line for 1^ by ^ inch bar down from its inter- 

 section with the horizontal line for 0.51 square inch of steel, which 

 gave a spacing of 9 inches, to its intersection with the vertical line 

 for 10-inch spacing; project hoiizontally from this intersection to 

 radial line 25 for diameters for steel, then vertically to cmve 2, again 

 horizontally to the intersection with the vertical line for 25 feet di- 

 ameter at the right-hand side of the page. This intersection wiU be 

 found to be on the diagonal line for 50 feet height of grain; 50 feet 

 from the top, therefore, we can change the spacing from 9 inches to 

 10 inches. 



Starting from the intersection of the diagonal line for 1 J by ^ inch 

 bars with the vertical line for 12-inch spacings, we find in the same 

 manner that at the height of 32 feet from the top we can increase the 

 spacing from 10 inches to 12 inches. 



We can now either continue to increase the spacing or maintain a 

 constant spacing of 12 inches and change the size of the bar. Select- 

 ing 1 by J inch as the next size bar, proceed as before from the inter- 

 section of its diagonal line with the 12-inch spacing line, and we find 

 that at a distance of 16 feet from the top this size bar can be substi- 

 tuted for the li by 5 inch. In the same manner we will find that 

 1 by J inch bars at 12 inches on center may be used for the last 9 feet. 



EXAMPLE 3. 



Required: Horizontal reinforcing for the full height in a wall of a 

 concrete bin 10 feet by 10 feet by 60 feet in height (/g = 16000,/^ = 650, 

 71= 15, and, for an intermediate span, m= 12). 



From Plate II: L, the unit lateral pressure at the bottom, = 300 

 pounds. 



FromTaUel: For^ = j^ = 6, ^ = 29.92,L = 29.92xl0 = 300pounds. 



., 300X10X10X12 „^^n^. •, 1 



M= Y2 ^ 30,000 men-pounds. 



