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THE POPULAR SCIENCE MONTHLY. 



the flanged girder, the top part of the truss and the top flange are 

 always in compression ; so the lower chord is always in tension, 

 as the lower flange in the flanged girders. This principle is the 

 same in all framed girders. 



Fig, 13 



Either of these trusses can be inverted whenever it is desired, 

 so that the truss comes below the floor, as shown in Figs. 13 and 

 14 ; the only difference that it makes is in the character of the 

 strain that comes upon the different members of the truss. The 



vertical member in the upright truss is in tension, and when the 

 truss is inverted it is in compression, as shown in the drawing. 

 The braces become ties, and the floor stringers are in compression. 

 Whenever it is desired to make the floor come upon the top of 

 the truss, then the bottom chord or tie-rods can be omitted en- 

 tirely, and the horizontal thrust taken by means of the masonry 



