On a structural plan, you see the notation '#4 @ 12" O.C.' What does this specify?
Correct Answer
D) 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 structural engineering terminology for reinforcing steel placement. The '#4' refers to Number 4 rebar, which has a 1/2-inch diameter and is one of the most commonly used rebar sizes in construction. The '@ 12" O.C.' means the bars are spaced at 12-inch intervals measured from center to center of each bar. This notation is universally used on structural plans to specify reinforcement requirements for concrete construction.
Why the Other Options Are Wrong
Option A: 4-inch pipe at 12-inch centers
The '#' symbol in structural plans specifically denotes rebar size numbers, not pipe dimensions. Pipe specifications would use different notation such as 'PVC' or 'ABS' with actual diameter measurements. Additionally, pipe placement wouldn't typically use 'on center' spacing terminology in structural drawings.
Option B: 4 gauge wire at 12-inch intervals
Wire gauge uses 'AWG' (American Wire Gauge) notation, not the '#' symbol used here. Electrical wire specifications on plans would include wire type, voltage rating, and conduit information. The '#' symbol is exclusively used for rebar numbering in structural contexts.
Option C: 4-inch bolts spaced 12 inches on center
Bolt specifications on structural plans would indicate actual diameter measurements (like '1/2" bolt' or '5/8" bolt') rather than using the '#' numbering system. Bolts are typically specified with their actual dimensions, thread pitch, and grade markings, not rebar numbering conventions.
Memory Technique
Remember: '#' = rebar Number, 'O.C.' = On Center spacing. Think '#4 bars = Four-bar spacing' - the number tells you the rebar size, and O.C. tells you center-to-center distance.
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