Page 319 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

Brockenbrough_Ch07.qxd 9/29/05 5:16 PM Page 7.3

FLOOR AND ROOF SYSTEMS

FLOOR AND ROOF SYSTEMS 7.3

FIGURE 7.2 Cellular steel deck with concrete slab.

For feeding wiring into the cells, a trench header is placed within the concrete above the metal deck,
in a direction perpendicular to the cells (Fig. 7.4). Special attention should be given to the design of the
structural components adjacent to the trench header, since composite action for both the floor deck and
beams is lost in these areas. Where possible, the direction of the cells should be selected to minimize the
total length of trench header required. Generally, by running the cells in the longitudinal direction of the
building, the total length of trench header is significantly less than if the cells were run in the transverse
direction (Fig. 7.5).
If a uniform grid of power outlets is desired, such as 5 ft by 5 ft on centers, preset outlets can be
positioned above the cells and cast into the concrete fill. However, in many cases the outlet locations
will be dictated by subsequent tenant layouts. In such cases, the concrete fill can be cored and after-
set outlets can be installed at any desired location.
Shored versus Unshored Construction. To support the weight of newly placed concrete and the
construction live loads applied to the metal deck, the deck can either be shored or be designed to span
between supporting members. If the deck is shored, a shallower-depth or thinner-gage deck can be
used. The economy of shoring, however, should be investigated, inasmuch as the savings in deck cost
is frequently more than offset by the cost of the shoring. Also, slab deflections that will occur after the
shoring is removed should be evaluated, as well as concrete cracking over supporting members.

FIGURE 7.3 Blended deck, alternating cellular and noncellular panels, in composite construction.

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