UNIVERSAL PORTLAND CEMENT CO. 
89 
The roof frame may be boarded up as shown in the plan view, with 
boards running either radially or otherwise, as desired. These boards 
should be placed close together to prevent the concrete from coming 
through when placed upon them. The table below shows the vertical 
rise to be given to roofs for silos of various diameters. 
A hole about feet square must of course be left for filling the silo, 
or if a roof covers a tank the hole will afford access to the latter. Before 
placing the reinforcing or the concrete, the top of the framing should be 
covered with building paper, or similar material, which will prevent the 
concrete from sticking to the forms. This will greatly facilitate their 
removal. 
The upper right hand quadrant of the plan and the sectional view 
show the spacing of the radial and hoop reinforcing. The radial reinforcing 
Placin the '^^ placed so as to be two feet apart on the circumference, and 
Reinforcing hoop reinforcing is indicated on the design. Extra rods 
should be put in around the window opening if the regular rods 
do not follow the outline of the window closely enough to reinforce it. 
All intersections must be wired together, and the outer ends of the 
radial wires brought down and bent around the horizontal reinforcing 
in the cornice, as shown. The reinforcing should be supported one inch 
above the roof frame, so that when the concrete is put on, the rods will 
rest on a one-inch bed and be covered by a three-inch bed, the total 
thickness of the roof being four inches. For amounts of reinforcing 
necessary for roofs of various diameters, use the table below. 
Table of Dimensions and Materials for Roofs for Silos with 
Diameters 8 Feet to 22 Feet 
J4 Inch Reinforcing Rods 
Diam- 
eter of 
Silo 
Verti- 
cal 
Rise 
Volume 
of Cone, 
in cu. yds. 
Cement 
Required 
barrels 
Sand 
Required 
cu. yds. 
Stone 
Required 
cu. yds. 
No. of 
Rods 
Required 
Stock 
Length 
of Rods 
No. of 
Lbs. of 
Rods 
10 ft. 
12 ft. 
14 ft. 
16 ft. 
23^ ft. 
3 ft. 
^y, ft. 
4 ft. 
1.60 
2.20 
2.90 
3.80 
2.80 
3.80 
5.00 
6.60 
.80 
1.10 
1.50 
2.00 
1.20 
1.70 
2.20 
2.90 
31 
33 
45 
87 
12 ft. 
16 ft. 
16 ft. 
10 ft. 
62 
88 
120 
146 
18 ft. 
20 ft. 
22 ft. 
4 ft. 
4 ft. 
4 ft. 
4.50 
5.40 
6.40 
7.8 
9.4 
11.1 
2.60 
2.80 
3.30 
3.50 
4.20 
4.90 
93 
107 
113 
12 ft. 
12 ft. 
14 ft. 
187 
226 
265 
Concrete for roofs is made of 1 sack Portland Cement to 2 cubic feet 
of coarse sand to 3 cubic feet of screened gravel or crushed stone. Each 
cubic yard of concrete requires 1% bbls. of cement, Y2 cubic yard of sand, 
and ^ cubic yard of gravel or stone, approximately. The 3^-inch reinforc- 
ing rod weighs 16.7 pounds per 100 feet. 
Concrete for the roof should be made in the proportion of one sack of 
cement to two cubic feet of coarse, clean sand, to three parts of screened 
