ACI 318-19 Section 7.3 & 7.6 | One-Way Slab Thickness & Reinforcement
One-way slabs bend primarily in a single direction across the shorter span. To avoid tedious deflection calculations on routine floors, ACI 318-19 Table 7.3.1.1 provides span-to-depth ratios (such as l/20 for simply supported and l/28 for both ends continuous) along with minimum temperature and shrinkage reinforcement.
Governing Formula
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Notation & Variables
Worked Example
Determine minimum thickness
For a 14-foot interior continuous span (l = 168 in) with Grade 60 rebar: h_min = 168 / 28 = 6.0 inches.
Calculate minimum steel area
For a 12-inch design strip with h = 6.0": As,min = 0.0018 × 12 × 6.0 = 0.130 in²/ft.
Check maximum bar spacing
Per §7.7.2.3, primary flexural bar spacing shall not exceed min(3h, 18") = 18.0 inches.
When does this govern?
Controls floor slab thickness in parking decks, corridor slabs, and beam-and-slab framing systems.
Common Mistake
Using effective depth d instead of total slab thickness h when computing minimum slab reinforcement As,min = 0.0018 b h.