Seismic design categories rank a structure's earthquake risk from A to F. They guide engineers in applying appropriate resistance measures, influencing everything from structural systems to non-structural components like windows and ceilings.
Determining the right category involves assessing regional hazards, soil conditions, and building use. Importance factors then fine-tune the design, increasing forces for critical structures to ensure better performance during earthquakes.
Seismic Design Categories
Seismic design categories (SDC)
- Classification system for structures ranks seismic risk from A (lowest) to F (highest)
- Determines level of seismic analysis required for building design
- Influences selection of structural systems and detailing requirements
- Impacts design of non-structural components (windows, ceilings)
- Guides engineers in applying appropriate seismic resistance measures
Determination of appropriate SDC
- Seismic hazard level of region assessed using USGS hazard maps
- Soil conditions at site classified (A to F) based on shear wave velocity
- Building's risk category evaluated considering occupancy and use
- Spectral response acceleration parameters calculated using site-specific data
- SDC lookup tables in building codes (ASCE 7) consulted for final determination
Importance Factors and Structural Classification
Importance factors in seismic design
- Numerical values reflect structure's significance to community safety
- Modify design seismic forces, typically ranging from 1.0 to 1.5
- Increase design forces for critical structures ensuring higher performance
- Influence selection of seismic design parameters (R, Cd)
- Applied in base shear calculation: $V = C_s W I$, where I is importance factor
Assignment of importance factors
- Low hazard structures assigned 1.0 (agricultural facilities, storage sheds)
- Standard occupancy structures given 1.0 (residential buildings, offices)
- High occupancy structures receive 1.25 (schools, large assembly areas)
- Essential facilities assigned 1.5 (hospitals, fire stations, power plants)
- Evaluate structure's function, occupancy, and failure consequences
- Refer to building code tables (ASCE 7-16 Table 1.5-2) for specific values
- Higher factors lead to more conservative designs, increased material use