PART 4 — STRUCTURAL DESIGNUpdated for the 2024 Ontario Building Code
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4.1.8.5.Importance Factor and Seismic Category
(1) The earthquake importance factor, IE, shall be determined according to Table 4.1.8.5.-A.
(2) Buildings shall be assigned a Seismic Category in accordance with Table 4.1.8.5.-B.
Table 4.1.8.5.-A
Importance Factor for Earthquake Loads and Effects, IE
Forming Part of Sentence 4.1.8.5.(1)
Importance Factor, IE
Importance Category
ULS SLS(1)
Low 0.8
Normal 1.0 (2)
High 1.3
Post-disaster 1.5
Notes to Table 4.1.8.5.-A:
(1) See Article 4.1.8.13.
(2) See Appendix A.
Table 4.1.8.5.-B
Seismic Categories for Buildings
Forming Part of Sentence 4.1.8.5.(2)
Seismic Category(1) IES(0.2) IES(1.0)
SC1 IES(0.2) < 0.2 IES(1.0) < 0.1
SC2 0.2 ≤ IES(0.2) < 0.35 0.1 ≤ IES(1.0) < 0.2
SC3 0.35 ≤ IES(0.2) ≤ 0.75 0.2 ≤ IES(1.0) ≤ 0.3
SC4 IES(0.2) > 0.75 IES(1.0) > 0.3
Notes to Table 4.1.8.5.-B:
(1) The Seismic Category of a building shall be taken as the more severe of the categories determined on the basis of IES(0.2) and IES(1.0), irrespective of
the fundamental lateral period of the building, Ta.
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Code text is reproduced for reference from the Ontario Building Code (O. Reg. 163/24, 2024 Building Code Compendium). This page is provided for general information and is not an official copy. Always verify requirements against the official Ontario Building Code and confirm with your local building department.