UNIVERSAL PORTLAND CEMENT CO. 
73 
Example diameter and 42 feet high, inside dimensions. The chart 
has six columns, one for each diameter. Each column shows 
the sizes of round rods and spacing for a silo 60 feet high. For a silo 42 
feet high the reinforcing will be exactly the same as for the upper 42 feet 
of a 60-foot silo, so that the chart may be used for all heights. At the 
left are jfigures showing the distance from roof down. Locate the 14-foot 
column at the top of the chart and run your finger down to the cross line 
marked 42 feet. That is the bottom of your silo. Now read off the sizes 
and spacing for the first 12 feet, from 42 up to 30 feet. It will require 
^-inch rods, spaced 6 inches apart. For the next 12 feet, from the 
30-foot level up to 18 feet from the top, ^-inch rods are still to be used 
but spaced 8 inches apart. You have now taken care of the first 24 feet. 
There are 18 feet more to build. From the 18-foot line up to the roof, 
%-inch rods are again to be used but spaced wider apart, 12 inches, because 
the weight of the silage above is less. In this case only ^/^-inch rods are 
required, but other heights and diameters call for rods from 3^-inch to 
jx^-inch in size. 
If you wish to build a silo 16 feet in diameter and 60 feet high, you 
will read off the sizes and spacing of rods from the 16-foot column, start- 
ing up from the bottom, at the line marked 60 feet. 
The horizontal reinforcing for the chute is the same for all sizes of 
silos. It consists of ^/g-inch round or twisted square rods spaced 18 inches 
apart. 
Reinforcing rods are sold by weight in stock lengths. One-quarter- 
inch rods weigh 16.84 pounds per 100 feet. Three-eighths-inch round 
rods 37.5 pounds per 100 feet. One-half-inch round rods 66.7 pounds 
per 100 feet. 
The work of constructing the silo will be made much easier if a con- 
venient method of hoisting materials is adopted at the start. The old 
Hoisting scheme of raising the concrete by hand with a rope and a bucket 
Materials wastes time and materials and means much unnecessary labor. 
Materials may best be raised with a rope and pulley, the latter 
attached either to a derrick frame, as shown on page 61, or suspended 
from a frame resting on top of forms, the power in either case being fur- 
nished by a horse. The derrick shown in the figure may be built to 
any height required, in the following manner: Pieces marked "A" 
(2x6 inches, 16 feet long) are spliced together until a height at least 6 feet 
greater than that of the completed walls is obtained. Pieces "B" (1x6 
inches) are nailed to " A " in such a manner as to make an I-beam as shown 
in the sectional view in the center. The cross arm is made of a 2x6-inch 
piece 3 feet long spiked to piece "A" and prevented from raising at the 
back end by piece "B" which runs flush with the top of the arm. The 
brace is made of 2x6-inch material, 3 feet 2 inches long. The three No. 9 
guy wires are fastened to the cross arm and brought around in grooves 
provided for the purpose and fastened to stakes driven in the ground for a 
considerable distance from the bottom of the derrick. This device, which 
has been recommended by the Iowa Experiment Station, is said to have 
been tested and found safe for loads less than 400 pounds. 
