Clause 7.2.2 assigns an importance factor I to buildings based on their functional use and post-earthquake significance. Higher importance factors amplify the design seismic force to provide a greater margin of safety for buildings whose collapse would cause greater loss of life or whose continued function is critical after an earthquake.
Key Requirements
•Importance factor I shall be taken from Table 8 based on building use
•Buildings with higher consequences of failure get higher I values
•For buildings not listed in Table 8, the designer shall use the closest matching category
•The importance factor directly multiplies the design seismic coefficient Ah
Reference Tables
Table 8 — Importance Factor I (Clause 7.2.2)
Structure Category
Importance Factor I
Buildings of low hazard to life (agricultural, minor storage)
1
All other buildings (residential, commercial, industrial)
1
Important buildings (schools, assembly halls, hospitals, large community halls, shopping malls, cinema halls, fire stations)
1.2
Critical and lifeline buildings (hospitals with surgery/emergency, fire stations, telephone exchanges, TV stations, water/power supply buildings, emergency shelters, air traffic control, large community halls for post-earthquake shelter)
1.5
For any building of more than one use, the highest applicable importance factor shall be used.
Practical Notes
✓Most residential and commercial buildings use I = 1.0
✓Schools, hospitals, and assembly buildings should use I = 1.2 or 1.5 depending on critical function
✓When a building serves multiple functions, always use the highest applicable I value
✓Client or local authority may specify a higher I value than the code minimum
Common Mistakes
⚠Using I = 1.0 for schools and hospitals — these require I = 1.2 or 1.5
⚠Not considering the post-earthquake function when selecting I — a building that must remain operational needs higher I
⚠Confusing importance factor with risk category nomenclature from international codes (ASCE 7)