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