Suppose a girder is required to support a floor 38 ft. by 30 ft., the girder to run the 38-ft. way. A single girder of 38ft. span down the centre of the room would require to be of steel, composed of a rolled joist 20in. by 7 1/2in. by 891b., with two 12-in. by 5/8-in. plates on each flange, making the whole girder 22 1/2in. by 12 in. by 1951b. per ft. The floor may then be carried by 11-in. by 3-in. fir joists resting on a 3 1/2-in. by 3 1/2-in. by 1/2-in. angle steel, riveted to webon each side, as shown in the accompanying illustration.

Girder to Support a Floor.