The use of wood or steel for girders will require different methods of construction. If wooden girders are used they may be set wholly or partially below the floor timbers, or flush with them. If there are no objections to dropping the girder below, this is the simplest and strongest construction. In this case, the floor beams should be sized down on the girders to maintain a perfectly level floor line, and a full bearing should be obtained for each timber. Where the girders are large the timbers may be brought to butt against each other upon the girder; and they should be secured end to end by iron dogs which turn down into each timber. (Fig. 177.) For small girders and light timbers, it will be better to let the timbers lap close and be spiked to each other, as in Fig. 178. When the girders are near together, and the timbers long enough to span two divisions, a rigid floor may be obtained by "breaking joints" with the floor timbers every five or six feet.

Fig. 176. Seating of Girder on Column.

Fig. 176. Seating of Girder on Column.

Fig. 177. Iron Dog.

Fig. 177. Iron Dog.

Fig. 178. Spiking of Joists.

Fig. 178. Spiking of Joists.