The Occupancy Category of a building as per BNBC 2020 or ASCE 7-05 refers to the classification of buildings and structures based on their use, importance, and the consequences of their failure. This classification influences the design requirements for seismic, wind, and other environmental loads.
BNBC 2020 or ASCE 7-05 defines four occupancy categories, as outlined below:
Occupancy Category I
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Definition: Buildings and structures that represent a low hazard to human life in the event of failure.
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Examples:
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Agricultural facilities
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Minor storage facilities
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Certain temporary facilities
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Occupancy Category II
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Definition: Buildings and structures that are not explicitly included in Categories I, III, or IV.
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Examples:
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Most residential, commercial, and industrial buildings
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Occupancy Category III
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Definition: Buildings and structures that could pose a substantial risk to human life or have significant societal impacts in the event of failure.
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Examples:
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Schools
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Buildings with a high occupancy load (e.g., theaters, sports arenas)
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Certain critical infrastructure (e.g., water treatment facilities serving large populations)
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Occupancy Category IV
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Definition: Buildings and structures that are essential to post-disaster recovery or are critical for public safety.
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Examples:
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Hospitals
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Emergency response centers
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Power-generating stations
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Water storage facilities for emergency fire suppression
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Aviation control towers
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Why the Classification Matters
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Higher Occupancy Categories require stricter design criteria to ensure the safety and operational functionality of the structures during and after extreme events such as earthquakes, hurricanes, or floods.