In California seismic design, buildings located in areas with mapped spectral response acceleration parameter Ss ≥ 1.5g are assigned to which Seismic Design Category when Risk Category II applies?
Correct Answer
D) SDC F
CBC Table 1613.3.5(1) assigns buildings to Seismic Design Category F when the mapped spectral response acceleration parameter Ss is equal to or greater than 1.5g for Risk Category II structures. This represents the highest seismic design category in California's most seismically active regions.
Why This Is the Correct Answer
CBC Table 1613.3.5(1) assigns Risk Category II buildings to Seismic Design Category F when the short-period spectral acceleration Ss is ≥ 1.5g. SDC F is the most severe seismic design category, applied to high-occupancy structures (Risk Category II) in California's most seismically intense zones. It triggers the most stringent structural system restrictions, detailing requirements, and geotechnical investigations.
Why the Other Options Are Wrong
Option A: SDC D
SDC D is a significant seismic category but falls below the threshold triggered by Ss ≥ 1.5g for Risk Category II. SDC D typically applies at lower acceleration values. Selecting D underestimates the seismic hazard for the given parameters.
Option B: SDC E
SDC E is reserved for Risk Category I and II buildings in areas with very high seismicity but is not the correct assignment when Ss ≥ 1.5g specifically — at that level, Risk Category II buildings advance to SDC F. SDC E is also less commonly encountered in standard CBC seismic tables than D or F.
Option C: SDC C
SDC C represents a moderate seismic risk category and is assigned at much lower spectral acceleration values. It would not apply to any building where Ss ≥ 1.5g — that acceleration level is firmly in the highest-risk territory.
Memory Technique
Think 'F is Final — the most Ferocious seismic category.' When Ss ≥ 1.5g, the ground shakes the hardest, so you need the final (most stringent) category: F. 'F = Fierce ground + Full restrictions.'
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