Section 11.6.1/Seismic Design Category
ASCE 7-22 Section 11.6 covers SDC determination from SDS, SD1, and risk category, governing all seismic design requirements.
The Seismic Design Category (SDC) is determined from Table 11.6-1 (based on SDS) and Table 11.6-2 (based on SD1), using the more severe category from the two tables. The SDC depends on the design spectral acceleration parameters (SDS and SD1) and the building's risk category (I through IV). SDC ranges from A (lowest seismic risk, minimal requirements) to F (highest seismic risk, most stringent detailing). SDC determines which seismic analysis methods are permitted, which lateral force-resisting systems can be used, the height limits for each system, and whether special detailing is required.
Why this section exists
The SDC is the single most consequential seismic parameter in building design. It determines whether a building needs only basic wind-level lateral design (SDC A) or full seismic detailing with special moment frames and shear walls (SDC D, E, F). A hospital in the same location as an office building gets a higher SDC because of its higher risk category, requiring more robust lateral systems. The SDC system efficiently matches the level of seismic design effort to the actual seismic risk and building importance.
What plan reviewers look for
Plan reviewers check the structural general notes for the SDC determination, including SDS, SD1, site class, and risk category. They verify the SDC from both Tables 11.6-1 and 11.6-2 and confirm the more severe governs. They check that the selected lateral system is permitted for the SDC per Table 12.2-1. They verify that the detailing provisions match the SDC (special detailing for SDC D through F).