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 uniform 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 ai” 
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 already outlined. In the present example, if we 
select 14 by 1 inch bar, 9 inches on center, as the reinforcing at the 
bottom, we can proceed as follows: 
Follow the diagonal line for 14 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 horizontally from this intersection to 
radial line 25 for diameters for steel, then vertically to curve 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 will 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 14 by 4 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 + 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 14 by } inch. In the same manner we will find that 
1 by + 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 (f; = 16000, f, = 650, 
n=15, and, for an intermediate span, m=12). 
From Plate II: L, the unit lateral pressure at the bottom, = 300 
pounds. 
From Table1: Fors, = = 6, a= 29.92,L = 29.92 x 10 =300 pounds. 
_30010x10x 12 
M 
19 = 30,000 inch-pounds. 
