Section 8.3.1/One-Way Slab Design
ACI 318-19 Chapter 8 covers one-way slab minimum thickness, flexural reinforcement, and shrinkage/temperature steel requirements.
One-way slabs must have a minimum thickness per Table 8.3.1.1 to control deflections without requiring a detailed deflection calculation. For a simply supported slab, the minimum thickness is L/20 (span/20). For one end continuous, L/24. For both ends continuous, L/28. For cantilevers, L/10. These ratios assume normal weight concrete and Grade 60 reinforcement. The slab must have flexural reinforcement sized for the factored moment at each section. Shrinkage and temperature reinforcement must be provided perpendicular to the flexural reinforcement at a minimum ratio of 0.0018 for Grade 60 bars.
Why this section exists
One-way slabs are the most common structural concrete element, forming the floors and roofs of most concrete buildings. The minimum thickness table provides a simple check that avoids complex deflection calculations for typical designs. Slabs thinner than the minimum may be structurally adequate for strength but will deflect excessively, cracking finishes, causing doors to bind, and creating a perception of an unsafe floor. The shrinkage and temperature reinforcement controls cracking from concrete shrinkage and thermal movements.
What plan reviewers look for
Plan reviewers check the slab thickness against the minimum from Table 8.3.1.1 for the span and support conditions. They verify the flexural reinforcement size and spacing against the factored moment. They check that shrinkage and temperature reinforcement is provided in the perpendicular direction. They verify concrete cover perSection 20.6.1. They check for reinforcement at the top of the slab over supports (negative moment reinforcement) in continuous slabs.