In California seismic design, a building located in Los Angeles with Site Class D soil conditions would typically be assigned to which Seismic Design Category for Risk Category II structures?
Correct Answer
B) SDC E
CBC Section 1613 and ASCE 7 maps show that Los Angeles has very high seismic ground motion parameters. Combined with Site Class D (stiff soil), Risk Category II structures typically fall into Seismic Design Category E, requiring enhanced seismic design provisions including special detailing requirements for structural elements.
Why This Is the Correct Answer
Los Angeles is in a zone of very high seismic ground motion. When combined with Site Class D (stiff soil, which amplifies ground shaking), Risk Category II structures are assigned to Seismic Design Category E. SDC E is triggered when the mapped short-period spectral acceleration (SDS) is ≥ 0.50g and the 1-second period acceleration (SD1) is ≥ 0.20g — conditions met in the LA basin, particularly on Site Class D soils.
Why the Other Options Are Wrong
Option A: SDC D
SDC D applies to buildings with high but not extreme seismic demand. In downtown Los Angeles with Site Class D amplification, the seismic parameters exceed SDC D thresholds and push the classification to SDC E. SDC D would be more typical of less seismically active areas of California.
Option C: SDC F
SDC F is reserved for Risk Category IV (essential facilities such as hospitals and emergency response centers) in areas with extreme seismic hazard. A standard Risk Category II building in Los Angeles would be SDC E, not F, regardless of soil class.
Option D: SDC C
SDC C reflects moderate seismic demand. The seismic ground motion in Los Angeles is far too high for a Risk Category II structure with Site Class D to land in SDC C. This would be typical of lower seismic-risk regions.
Memory Technique
In LA, the ground shakes hard (SDC E). Think: LA = Earthquake City → Site Class D soil amplifies it → Risk Category II goes to 'E for Extreme.' SDC F is for hospitals and firehouses (essential facilities) in extreme zones.
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