Seismic Design Categories
Building Code Resources – Seismic Design Categories
Seismic Design Categories: We understand navigating the complexities of project requirements can be a challenging task, as stressed by our valued customers. Whether you seek a deeper comprehension of how seismic requirements are determined or simply aim to fulfill project obligations, ISAT is here to help.
If you find yourself uncertain about the Seismic Design Category (SDC) applicable to your project, it is typically outlined in the structural notes section of your construction drawings or listed in the project specification. Should you encounter difficulties in determining the appropriate category, our knowledgeable team is readily available to guide you through your project details and assist in finding the right classification. Once the SDC is identified, utilize ISAT’s online Seismic Requirement Calculator to determine the specific seismic requirements for your project.
What is a Seismic Design Category?​
If A Seismic Design Category is a classification assigned to a structure based on its occupancy category, and the severity of the design earthquake ground motion. The category assignment can range from A-F, and can be defined as the following:
- Seismic Design Category A – Corresponds to buildings in areas where expected ground shaking will be minor. Good Soils.
- Seismic Design Category B – Corresponds to buildings of Occupancy Groups I, II and III where expected ground shaking will be moderate. Stratified soils with Good and poor Soils.
- Seismic Design Category C – Corresponds to buildings of Occupancy Groups IV (Hospitals, Police Stations Emergency control centers etc.) I where expected ground shaking will be MODERATE AND buildings of occupancy categories I, II, and III where MORE SEVERE ground shaking will occur.
- Seismic Design Category D -Corresponds to buildings and structures in areas expected to experience severe and destructive ground shaking But NOT located close to a major fault. Sites with poor soil are a good example.
- Seismic Design Category E – Corresponds to buildings of Occupancy Groups I, II and III in areas NEAR MAJOR ACTIVE FAULTS. Soil or rock is of no consequence.
- Seismic Design Category F – Corresponds to buildings of Occupancy Groups IV (Hospitals, Police Stations Emergency control centers etc.) areas NEAR MAJOR ACTIVE FAULTS. Soil or rock is of no consequence.
Determine Your Seismic Requirements
Once you have figured out the SDC of your project, you can then determine your seismic requirements by using ISAT’s online Seismic Requirement Calculator.
A Good Soils report from a Geotechnical engineer will and should provide to the structural engineer and architect the parameters necessary to determine the Seismic Design Category OR provide the Seismic Design category outright. However, it MUST be specified in their subcontract.
ASCE 7-16 Seismic Design Categories Reference Information
Structures shall be assigned a Seismic Design Category in accordance with this section. Risk Category I, II, or III structures located where the mapped spectral response acceleration parameter at 1-s period, S1, is greater than or equal to 0.75 shall be assigned to Seismic Design Category E. Risk Category IV structures located where the mapped spectral response acceleration parameter at 1-s period, S1, is greater than or equal to 0.75 shall be assigned to Seismic Design Category F. All other structures shall be assigned to a Seismic Design Category based on their Risk Category and the design spectral response acceleration parameters, SDS and SD1, determined in accordance with Section 11.4.5. Each building and structure shall be assigned to the more severe Seismic Design Category in accordance with Table 11.6-1 or 11.6-2, irrespective of the fundamental period of vibration of the structure, T. The provisions in Chapter 19 shall not be used to modify the spectral response acceleration parameters for determining Seismic Design Category.
Where S1 is less than 0.75, the Seismic Design Category is permitted to be determined from Table 11.6-1 alone where all of the following apply:
- In each of the two orthogonal directions, the approximate fundamental period of the structure, Ta, determined in accordance with Section 12.8.2.1 is less than 0.8Ts, where Ts is determined in accordance with Section 11.4.6.
- In each of two orthogonal directions, the fundamental period of the structure used to calculate the story drift is less than Ts.
- Eq. (12.8-2) is used to determine the seismic response coefficient Cs.
- The diaphragms are rigid in accordance with Section 12.3; or, for diaphragms that are not rigid, the horizontal distance between vertical elements of the seismic force-resisting system does not exceed 40 ft (12.192 m).
Where the alternate simplified design procedure of Section 12.14 is used, the Seismic Design Category is permitted to be determined from Table 11.6-1 alone, using the value of SDS determined in Section 12.14.8.1, except that where S1 is greater than or equal to 0.75, the Seismic Design Category shall be E.
11.7 DESIGN REQUIREMENTS FOR SEISMIC DESIGN CATEGORY A
Buildings and other structures assigned to Seismic Design Category A need only comply with the requirements of Section 1.4. Nonstructural components in SDC A are exempt from seismic design requirements. In addition, tanks assigned to Risk Category IV shall satisfy the freeboard requirement in Section 15.6.5.1.
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