3344Design Checks for the Concrete Slab

The top chord carries varying amounts of bending moment and axial force, as illustrated in Figure 33.7, but the most important areas are indicated as Points 4 to 6. The axial forces are always compressive in the concrete slab; the bending moments are positive at Points 5 and 6 but negative at Point 4. As a result, this location is normally the one that governs the performance of the slab, not the least because the reinforcement in the positive moment region includes the cross-sectional area of the steel deck.

The full effective width of the slab must be analyzed for combined bending and axial force at all of Points 4 through 6. Either the composite beam-column criteria of the AISC LRFD Specification [3] or the criteria of the reinforced concrete structures code of American Concrete Institute (ACI) [13] may be used for this purpose.

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