On a structural plan, you see the notation '#4 @ 12" O.C.' What does this specify?
Correct Answer
A) Number 4 rebar spaced 12 inches on center
The '#4 @ 12" O.C.' notation indicates Number 4 reinforcing bar (rebar) placed at 12-inch intervals on center, which is standard reinforcement specification notation.
Why This Is the Correct Answer
The '#4 @ 12" O.C.' notation is standard construction industry terminology for reinforcing steel specifications. The '#4' refers to Number 4 rebar, which has a diameter of 1/2 inch, while '@ 12" O.C.' means the bars are spaced at 12-inch intervals measured from center to center of each bar. This notation system is universally used on structural drawings to specify rebar size and spacing requirements.
Why the Other Options Are Wrong
Option B: 4-inch bolts spaced 12 inches on center
Bolts are typically specified with actual diameter measurements (like '1/2" bolts') rather than number designations, and bolt specifications would include additional information like bolt type, length, and material grade.
Option C: 4 gauge wire at 12-inch intervals
Wire gauge uses different numbering systems (AWG for electrical wire), and structural plans would specify wire mesh or welded wire fabric differently, typically as 'WWF' or 'WWR' with specific designations.
Option D: 4-inch pipe at 12-inch centers
Pipe specifications on structural plans would include actual diameter measurements and pipe schedule information (like '4" SCH 40'), not number designations, and would be clearly identified as piping rather than reinforcement.
Memory Technique
Think '#' = rebar number, and remember that #4 rebar = 4/8 inch = 1/2 inch diameter. 'O.C.' sounds like 'Oh See' - you can 'see' from center to center of each bar.
Reference Hint
ACI 318 Building Code Requirements for Structural Concrete, Chapter 20 - Steel Reinforcement, or Florida Building Code Chapter 19 - Concrete
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