CHAPTER IX. 



THE POLK SYSTEM. 



This system of silo construction is controlled by the 

 Polk-Genung-Polk Company of Fort Branch, Indiana. 

 It has as its basic principle of operation a center mast, 

 erected at the center of the floor of the structure and 

 carefully plumbed by means of guy wires attached to 

 the top and provided with turn-buckles. From this 

 mast everything used in the construction of the silo is 

 suspended, including the staging, the apparatus for 

 handling the forms, and the crane for hoisting and 

 depositing the concrete. 



The mast is a four-inch steel pipe, provided with a 

 series of transverse holes to receive a heavy steel pin. 

 This pin supports a widely flanged collar, which serves 

 to support the jacks by which the forms are lifted. 



Resting upon the jacks is a hub, consisting of a 

 flanged base collar and a top dished collar connected 

 by a central pipe of sufficient diameter to work easily 

 over the center mast. From the base collar of this hub 

 radiate steel tees which are supported from the upper 

 collar by adjustable hanger rods with chain clevises. 



Each form consists of eight separable sections, and 

 each section is reinforced and stiffened by a steel angle 

 frame around the edges. The inner and outer steel 

 wall-forms, which are rolled to the required curvature, 

 are bolted to the radiating steel tees. The outer sec- 

 tions are bolted together at their ends through holes in 

 the frames. The inner sections are similarly bolted 

 together, but carry steel wedges between them, the 



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