According to CBC Chapter 16A (California's seismic requirements), what is the minimum lap splice length for #4 reinforcing bars in concrete construction located in Seismic Design Category D?
Correct Answer
A) 24 inches
CBC Section 1613A.2.6 requires a minimum lap splice length of 24 inches for #4 reinforcing bars in Seismic Design Category D. This California-specific requirement addresses the state's high seismic risk and ensures adequate structural continuity during earthquake events.
Why This Is the Correct Answer
CBC Section 1613A.2.6 specifies a minimum lap splice length of 24 inches for #4 rebar in Seismic Design Category D. California's Chapter 16A contains seismic amendments to the IBC that impose stricter requirements than the base code, reflecting California's high seismic hazard. A 24-inch lap ensures adequate force transfer between bars during earthquake-induced stress cycling, maintaining structural continuity in concrete members when ground motion forces the bars to work dynamically.
Why the Other Options Are Wrong
Option B: 30 inches
30 inches exceeds the CBC requirement for #4 bars in SDC D. While longer splices provide more bond area, the code-specified minimum is 24 inches. Overstating requirements wastes material and can mislead on exam questions where the specific code value must be recalled.
Option C: 12 inches
12 inches is insufficient for seismic conditions and falls below the CBC Chapter 16A minimum. A 12-inch splice might apply in low-stress, non-seismic applications or for very small-diameter bars, but for #4 bars in SDC D — a high seismic zone — this length does not provide adequate force transfer.
Option D: 18 inches
18 inches is below the 24-inch minimum required by CBC 1613A.2.6 for this bar size and seismic category. This length may reflect non-seismic or lower-SDC requirements and would be non-compliant for California SDC D construction.
Memory Technique
California SDC D, #4 bar = '2 feet, no cheat.' 24 inches is the floor — California doesn't shortcut on seismic.
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