A structural plan shows reinforcing steel marked as '#5 @ 12" O.C.' What does this specification mean?
Correct Answer
B) Number 5 rebar spaced 12 inches on center
#5 refers to number 5 reinforcing bar (5/8-inch diameter), and @ 12" O.C. means the bars are spaced 12 inches on center. This is standard notation for reinforcing steel placement.
Why This Is the Correct Answer
Option B correctly interprets standard reinforcing steel notation. '#5' refers to Number 5 rebar, which has a nominal diameter of 5/8 inch (the number indicates eighths of an inch). The '@' symbol means 'at' and '12" O.C.' stands for '12 inches on center,' meaning the spacing between the centerlines of adjacent bars is 12 inches. This is the universal standard notation used in structural drawings for reinforcing steel placement specifications.
Why the Other Options Are Wrong
Option A: 5mm rebar with 12-inch overlap
This incorrectly interprets '#5' as 5mm diameter and 'O.C.' as overlap. The '#' symbol in US construction refers to rebar size numbers, not metric measurements. 'O.C.' stands for 'on center' (spacing), not overlap distance.
Option C: 5 pieces of rebar in a 12-inch span
This misinterprets the notation as quantity rather than size and spacing. '#5' refers to the rebar size (Number 5), not the number of pieces. The specification describes the size and spacing of individual bars, not how many bars fit in a span.
Option D: 5/8-inch diameter rebar at 12-foot centers
While correctly identifying 5/8-inch diameter, this incorrectly states '12-foot centers' instead of '12-inch centers.' The notation clearly shows '12"' (inches), not feet. Additionally, rebar spacing of 12 feet would be extremely unusual and impractical for structural reinforcement.
Memory Technique
Remember: Rebar # = eighths of inch diameter (so #5 = 5/8"), and O.C. = On Center spacing. Think 'Number Five at Twelve On Center' - size at spacing.
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