264 ILLINOIS STATE DAIRYMEN'S ASSOCIATION. 



due to the fact that the wall independent of the steel is able to 

 resist a part of the bursting pressure. 



In any cylindrical tank designed to resist bursting, the total 

 pressure tending to rupture a section of the tank varies as 

 the pressure and the diameter. If the diameter is uniform from 

 top to bottom, the stress tending to burst the walls varies as 

 the pressure. Thus in a silo where the pressure increases with 

 the depth the size of the hoops or reinforcement required at 

 the top is small, but must increase with the depth. 



Some vertical reinforcement for concrete is generally recom- 

 mended, although if the horizontal reinforcement is not spaced 

 too far apart, it seems to be of doubtful importance, as no 

 serious stresses are to be overcome in this direction. When 

 used it consists of about one %-inch rod spaced from 18 

 inches to 3 feet around the wall. The foregoing statement 

 does not apply to the sides of the door openings, which should 

 be carefully and thoroughly reinforced. 



Failure of Concrete Silos. 



Often more can be learned of a class of structures from a 

 failure than in any other way. As far as possible, all silo 

 failures were investigated. A silo visited and the details con- 

 nected with its failure obtained, is used by a canning company to 

 preserve the pea vines which would otherwise be a waste pro- 

 duct. It is 60 feet in diameter and 40 feet deep. The walls 

 are 19 inches thick at the bottom and 13 inches at the top. The 

 reinforcement consisted of J^-inch round steel rods, spaced 18 

 inches apart at the bottom and so spaced above that 22 rods were 

 used in the entire wall. There is an excess of juice in pea vines 

 and in order to prevent an accumulation of this and a consequent 

 excessive internal pressure, a large drain was placed at the 

 center of the silo. This drain for the first two years accom- 

 plished its purpose, but upon the third filling it became clogged, 

 allowing the juices to accumulate to a depth of at least 20 

 feet. By calculation it was determined that the bursting pres- 

 sure in the silo due to 20- feet of juice was more than double 

 the strength of the steel reinforcement in the wall for the bot- 



