According to the California Building Code (CBC), what is the minimum concrete cover required for reinforcing steel in cast-in-place concrete footings when cast against and permanently exposed to earth in California's seismic zones?
Correct Answer
A) 3 inches
CBC Section 1909.7.1 requires 3 inches of concrete cover for reinforcing steel in cast-in-place concrete when cast against and permanently exposed to earth. This increased cover provides protection against corrosion and ensures proper bond development, which is critical in California's seismic environment where structural integrity is paramount.
Why This Is the Correct Answer
CBC Section 1909.7.1 mandates 3 inches of concrete cover when reinforcing steel is cast against and permanently exposed to earth. This substantial cover protects rebar from ground moisture and corrosion while ensuring full bond development length — both critical in seismic zones where footings must perform under cyclic loading.
Why the Other Options Are Wrong
Option B: 1.5 inches
1.5 inches is the minimum cover for interior concrete not exposed to weather or earth. It is far too thin for footings cast directly against soil, where moisture exposure and corrosion risk are much higher.
Option C: 4 inches
4 inches exceeds the code minimum for earth-exposed footings. This cover might apply to very aggressive soil conditions (high sulfate or chloride environments) but is not the standard CBC requirement for typical footings.
Option D: 2 inches
2 inches is the minimum cover for concrete exposed to weather or in contact with soil in wall panels and thin members, not for footings cast against earth. The footing condition requires the higher 3-inch minimum.
Memory Technique
Remember the cover ladder: 1.5" inside → 2" exposed to weather → 3" cast against earth. Each step outward adds more cover. Footings go into the ground, so they get the most: 3 inches.
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