On a structural drawing, what does the symbol "#5 @ 12" O.C." indicate?
Correct Answer
B) Number 5 rebar spaced 12 inches on center
The # symbol indicates rebar size designation, where #5 refers to Number 5 rebar (5/8" diameter). The @ symbol means "at" and O.C. means "on center," so this indicates Number 5 rebar placed every 12 inches on center.
Why This Is the Correct Answer
The symbol '#5 @ 12" O.C.' follows standard construction notation where the # symbol indicates rebar size designation (Number 5 rebar), the @ symbol means 'at' or 'spaced at', and O.C. stands for 'on center'. Number 5 rebar has a 5/8 inch diameter and when spaced 12 inches on center, it means the centerline distance between each rebar is 12 inches. This is a fundamental reinforcement specification that appears frequently on structural drawings.
Why the Other Options Are Wrong
Option A: Number 5 rebar spaced 12 feet on center
Option B correctly identifies the diameter (5/8 inch) and spacing (12 inches on center) but incorrectly describes it as '5/8 inch rebar' instead of using the proper designation 'Number 5 rebar'. The # symbol specifically indicates the numbered rebar designation system.
Option C: 5/8 inch rebar spaced 12 inches on center
Option D misinterprets the notation entirely, suggesting 5 pieces of rebar in a 12-inch span rather than understanding that #5 refers to the rebar size and @ 12" O.C. refers to the spacing pattern.
Memory Technique
Think '# = Number, @ = At, O.C. = On Center' and remember that rebar numbers equal diameter in eighths: #5 = 5/8 inch diameter
Reference Hint
ACI 318 Building Code Requirements for Structural Concrete, Chapter 25 (Reinforcement Details) or construction drawing standards section in contractor reference materials
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