It is assumed that an assembly-room is to be built over three small shops and that it is proposed to put in rolled steel joists and fill in with concrete. For a clear span of 17ft. Tin. the least possible depth of steel joists for an assembly-room floor is 9 in., but a 10-in. by 4 1/2-in. by 30-lb. or 10-in. by 5-in. by 29-lb. section would be much better. These joists may be placed (3 ft. apart, and it would be an advantage if 3 1/2-in. by 1 1/2-in. by 6-lb. joists were placed transversely every 6 ft. between the others, connected by angle brackets and carried by 2-in. by 2-in. by 1/4-in. steel angles riveted to web of main girder joist. The concrete should be the best Portland cement to 5 sea-beach gravel, and 0 in. thick. The centring should remain undisturbed for three weeks after the concrete is put in, and in the meantime there should be no traffic over it.

Size of Rolled Joists for an Assembly room Floor.

Size of Rolled Joists for an Assembly-room Floor.