Structural Engineering · Engineering Glossary
The Seismic Design Category (SDC) is a classification (A through F) assigned to a building based on its geographic seismic hazard, occupancy category (risk category), and soil site class. The SDC determines which seismic design requirements, detailing provisions, and lateral force resisting system options apply to the building.
SDC A and B apply to low seismic hazard areas with minimal design requirements; SDC C through F apply to areas with progressively higher seismic hazard. Higher SDCs require more stringent detailing, more ductile lateral systems (such as Special Moment Frames or Special Shear Walls), more comprehensive seismic analysis, and greater redundancy. The site class (based on soil type — Class A is hard rock, Class E is soft soil) amplifies the ground motion for softer soils, which can push a project into a higher SDC. Apex Grid's structural engineers determine the SDC for every project early in design, as it drives fundamental decisions about the lateral force resisting system.
Apex Grid Engineering maintains this glossary as a resource for architects, contractors, developers, and property owners who encounter unfamiliar engineering terminology on their projects.
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