" Framed floors " are used for spans of 24 feet and over, and consist of girders placed 10 feet apart, in addition to the binders.
To save repetition, it may be said that framed floors have the same objects, advantages, and disadvantages, as double floors - but of course in a higher degree - and the same rules apply to both.
It should be borne in mind that two binders should never be tenoned into the girder at one place, as that would almost cut it in two, and weaken it too much; but they should be placed hit and miss fashion as X. (See fig. 290.) The method of jointing is shown in the sections A B, C D.
A better way to secure the binder to the girder, without cutting into the latter, is as fig. 292. An iron stirrup is hung over the girder, with a shoe on each side, to receive the binder. The stirrup is secured to the girder by a bolt at the head.
The girders of framed floors must necessarily be stronger in proportion than binders; and taking 13 inches deep by 11 inches wide - for a 20-feet span - as a basis (by the same rule as that for binders), adding 1 inch in depth and 1/2 an inch in width for each additional 2 feet in span, we have for -
20 feet span a girder
13 inches deep by
11 inches wide.
22 " "
11 1/2 "
24 " "
26 " "
12 1/2 "
28 " "
Ceiling joists are generally of uniform size - viz., 3 1/2 inches deep by 2 1/4 inches wide, and are fixed 12 or 73 inches apart; and they should have a bearing, whether on a wall or to a beam, at every 8 feet Iron binders and girders of different sections, in place of wood, are now used, chiefly for double and framed floors; the bridging and ceiling joists being fixed to wood plates bolted to the flanges of the wrought-iron binders, as fig. 293.
In framed floors the binders, with the wood bridging and ceiling joists, are placed between the top and bottom flanges of the girder, and connected with angle irons bolted to the flange of the girder, as fig. 294.
Wooden beams, binders, and girders are often flitched to strengthen them - that is, they are cut in half, and reversed with a thin wrought-
Sectional Plan at A A iron plate between them, as fig. 295, the three being bolted together transversely, as shown in the section.
Or, they are, in exceptional cases, trussed, as fig. 296, by a king truss, or by a queen truss, as in fig. 397.
The beam or girder is cut in half, and reversed as the last, but instead of the flitch plate a framed truss, composed of wrought-iron abutments and hardwood struts, is bolted between the two halves, as shown.
Another, though inconvenient, method of trussing is as figs. 298 and 299, which explain themselves, the shoes, Z Z, and stays, Y Y, being of cast iron, and the rods, X X, being of wrought iron to resist the tension. In this case the beam is not cut in two, but the rods go through it, as illustrated. The strength of the truss depends on the length of the struts from the beam, and consequently the stronger it is made the more inconvenient and unsightly it becomes. This is on the same principle as that often seen when thin boards are strengthened to carry flower-pots by strutting underneath, and tying tight a piece of string from each end of the board over the strut.