Two parallel layers of cast-in-place reinforcing bars are being checked before concrete placement. Which ACI minimum clear spacing rule applies to parallel bars in a layer?
Correct Answer
D) At least the greatest of 1 in., one bar diameter, and 4/3 times the nominal maximum aggregate size
ACI 318 minimum clear spacing for parallel bars in a layer is the greatest of 1 in., the bar diameter, and 4/3 times the nominal maximum aggregate size. Other choices: 1/2 in. is too small, bar diameter alone omits other limits, and a universal 2 in. rule is not the ACI expression.
Why This Is the Correct Answer
ACI 318 minimum clear spacing for parallel bars in a layer is the greatest of 1 in., the bar diameter, and 4/3 times the nominal maximum aggregate size.
Why the Other Options Are Wrong
Option A: At least 1/2 in. regardless of aggregate size
Choice A gives At least 1/2 in. regardless of aggregate size. Its specific error: At least 1/2 in. regardless of aggregate size is a different published number than the cited Clear bar spacing value; ACI 318-19 25.2.1 supports At least the greatest of 1 in. on.
Option B: Exactly one bar diameter, with no aggregate-size check
Choice B (Exactly one bar diameter, with no aggregate-size check) is rejected because it points to Exactly one bar diameter, with no aggregate-size check, but.
Option C: At least 2 in. for every reinforced member
In concrete work, At least 2 in. for every reinforced member is the wrong selection for Clear bar spacing: At least 2 in. for every reinforced member is a different published number than the cited Clear bar spacing value; ACI 318-19 25.2.1 supports At least the greatest of 1 in.
Memory Technique
Make clear bar spacing a tabbed card: cite the exact condition, then choose At least the greatest of 1 in., one bar diameter, and 4/3 times the nominal maximum aggregate size.
Reference Hint
Open ACI 318-19, Building Code Requirements for Structural Concrete; use ACI 318-19 25.2.1 to confirm that ACI 318 minimum clear spacing for parallel bars in a layer is the greatest of 1 in., the bar diameter, and 4/3 times the nominal maximum aggregate size.
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