CSLB General Building (B)Site Work, Foundations and ConcreteMedium
A structural plan calls for #8 rebar (1-inch diameter) to be placed in a footing with a maximum aggregate size of 1 inch. According to ACI 318 minimum clear spacing requirements, what is the minimum required clear spacing between the bars?
- A1 inch
- B3/4 inch
- C2 inches
- D1-1/3 inches
Show answer & explanationAnswer & explanation
Correct answer: D. 1-1/3 inches
ACI 318 requires minimum clear spacing to be the greatest of: bar diameter (1 in), 1 inch, or 4/3 times the maximum aggregate size (4/3 × 1 in = 1.33 in). Since 1.33 inches is the largest value, it governs and becomes the minimum required clear spacing.
Why the other options are wrong
- A. 1 inch satisfies two criteria but not the aggregate-based requirement.
- B. 3/4 inch is smaller than all three minimums and does not satisfy the code.
- C. 2 inches exceeds the code minimum; it's not incorrect to use but not the required minimum.
Rebar Minimum Clear Spacing
ACI 318 requires rebar clear spacing to be the greatest of the bar diameter, 1 inch, or 4/3 the maximum aggregate size, ensuring proper concrete flow and consolidation around bars.
- Three criteria: bar diameter, 1 inch, 4/3 max aggregate size
- The largest value governs
- Prevents honeycombing and ensures proper bond
Memory trick: Pick the biggest of three rules — aggregate often wins.