ACI 318-19 Table 20.5.1.3.1 | Specified Concrete Cover for Reinforcement
Concrete cover is the protective distance between outer steel rebar and the concrete surface. Adequate cover protects steel from rusting when exposed to moisture and preserves structural integrity during fires.
Governing Formula
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Notation & Variables
Worked Example
Identify member exposure
Design an isolated footing poured directly on undisturbed soil with Grade 60 steel.
Look up required cover
Because the concrete is cast against and permanently in contact with earth without formwork, minimum specified cover is 3.0 inches (75 mm).
Calculate effective depth d
For a 24-inch thick footing with #8 bottom bars, effective depth is d = 24 - 3.0 - (1.0 / 2) = 20.5 inches.
When does this govern?
Always dictates the initial section layout and effective depth (d) for flexural and shear capacity calculations.
Common Mistake
Measuring concrete cover to the center of longitudinal bars instead of the outer edge of stirrups or ties, resulting in under-covered stirrups that corrode prematurely.