Page:Popular Science Monthly Volume 36.djvu/484

468 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.



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