Building Design and Construction Handbook - Merritt - Ventech!

7.42 SECTION SEVEN
Temporary coverage and working platforms are quickly placed. The open space
between joists, and through the webs, may be utilized for ducts, cables, light fixtures,
and piping. A thin floor slab may be cast on steel lath, corrugated-steel sheets,
or wire-reinforced paper lath laid on top of the joists. A plaster ceiling may be
suspended or attached directly to the bottom flange of the joists.
Lightweight beams, or so-called ‘‘junior’’ beams, are also used in the same
manner as open-web joists, and with the same advantages and economy, except
that the solid webs do not allow as much freedom in installation of utilities. Beams
may be spaced according to their safe load capacity; 3- and 4-ft spacings are common.
As a type, therefore, the lightweight-steel-beam floor is intermediate between
concrete arches and open-web joists.
7.13.2 Cellular-Steel Floors
Cold-formed steel decking is frequently used in office buildings. One type is illustrated
in Fig. 7.24. Other manufacturers make similar cellular metal decks, the
primary difference being in the shape of the cells. Often, decking with half cells is
used. These are open ended on the bottom, but flat sheets close those cells that
incorporate services. Sometimes, cells are enlarged laterally to transmit air for air
conditioning.
Two outstanding advantages of cellular floors are rapidity of erection and ease
with which present and future connections can be made to telephone, computer,
light, and power wiring, each cell serving as a conduit. Each deck unit becomes a
working platform immediately on erection, thus enabling the several finishing trades
to follow right behind the steel erector.
Although the cost of the steel deck system may be larger than that of other floor
systems, the cost differential can be narrowed to competitive position when equal
consideration for electrical facility is imposed on the other systems; e.g., the addition
of 4 in of concrete fill to cover embedded electrical conduit on top of a
concrete flat-slab floor.
In earlier floors of this type, the steel decking was assumed to be structurally
independent. In that case, the concrete fill served only to provide fire resistance
and a level floor. Most modern deckings, however, are bonded or locked to the
concrete, so that the two materials act as a unit in composite construction. Usually,
only top-quality stone concrete (ASTM C33 aggregates) is used, although lightweight
concrete made with ASTM C330 aggregates is an acceptable alternative.
FIGURE 7.24 Cellular-steel floor construction.