Commercial Building Inspector B2Structural SystemsMedium
A structural designer is calculating the seismic design forces for a new commercial building located in a high seismic region. The building is classified as Risk Category III. Which of the following seismic design parameters is directly influenced by the Risk Category?
- ASeismic Design Category (SDC)
- BSpectral Response Accelerations (Ss and S1)
- CImportance Factor (Ie)
- DSite Class
Show answer & explanationAnswer & explanation
Correct answer: C. Importance Factor (Ie)
The Importance Factor (Ie) is a seismic design parameter that directly reflects the Risk Category of a building. Buildings with higher Risk Categories (e.g., Risk Category III or IV) have higher Importance Factors, which result in increased seismic design forces to ensure a greater level of life safety and post-earthquake functionality.
Why the other options are wrong
- A. Seismic Design Category (SDC) is determined by both the Risk Category and the mapped spectral response accelerations (Ss and S1). While related, the Risk Category influences SDC through Ie.
- B. Spectral Response Accelerations (Ss and S1) are determined by the geographic location on seismic hazard maps, not the building's Risk Category.
- D. Site Class (A-F) is determined by soil properties, not building Risk Category.
Seismic Importance Factor (Ie)
A factor applied to seismic design forces to account for the occupancy and use of a building, reflecting its importance for public safety and post-earthquake functionality, directly tied to its Risk Category.
- Ranges from 1.0 to 1.5 (typically).
- Higher for essential facilities (Risk Category IV) and special occupancy structures (Risk Category III).
- Increases seismic forces for critical buildings.
Memory trick: Seismic design factors build from location and use.