310 ILLINOIS STATi^ DAIRYMEN'S ASSOCIATION. 



tied to adjacent buildings and held to place by guy wires. The 

 importance of this feature is emphasized through the fact that 

 certain insurance companies do not care to insure such types of 

 silos and either will not insure at all or only when extra charge 

 is made for exposure. The Iowa silo is rigid enough and heavy 

 enough so that it is not affected by wind. 



Enough steel reinforcement is laid in the mortar joints of 

 the Iowa silo to carry the entire bursting pressure of the silage 

 with a reasonable factor of safety. Originally, the safe working 

 load of the steel was taken at 20,000 pounds per square inch, 

 which gives a factor of safety of three for steel rolled in relative- 

 ly large bars. As it has been found that steel wire is the most 

 desirable reinforcement, the safe working strength has been rais- 

 ed to 30,000 pounds per square inch. The drawing process 

 through which wire must pass in its manufacturing increases its 

 tensile strength and this change on the part of the designers is en- 

 tirely justified as there is no reduction in the strength of the 

 reinforcement. As originally designed, practically as much 

 steel was included in the walls of the Iowa silo as was to be 

 found in the hoops of the average stave silo which not only must 

 resist the bursting pressure of the silage, but the swelling action 

 of the staves. The form of reinforcement which has been found 

 the most convenient for the Iowa silo is hard black. No. 3 steel 

 wire which is laid in the mortar joints as described later. 



Some silo walls have been known to crumple at the bottom, 

 due to the weight of the walls themselves and to the friction of 

 the silage. The 4-inch block wall of a 16-foot Iowa silo, 35 feet 

 high, will carry not only its own weight at the bottom, but that 

 of all the silage which could be placed in the silo several times 

 over. 



When constructed of curved blocks, the Iowa silo has been 

 made reasonably smooth on the inside, there has been no loss 

 of silage from the roughness of the wall. Silo No. i, which was 

 constructed of 16-inch blocks with little curvature, permitted a 

 few air pockets to form, resulting in a small amount of spoiled 

 silage after being stored in the silo for two years. 



