The NSR-10 places every building in one of four occupancy groups, and depending on the group it multiplies the seismic design forces by an importance factor: 1.00 for group I, 1.10 for group II, 1.25 for group III and 1.50 for group IV (A.2.5 and table A.2.5-1). A hospital with an emergency department is designed for forces 50% larger than a home.
The four groups
Group IV, essential facilities: hospitals and clinics with surgery, intensive care or emergency services; airports and telecommunications centers; emergency shelters; power and water plants. Group III, community services: fire stations, police, civil defense, and also daycare centers, schools and universities. Group II, special occupancy: halls for more than 200 people, shopping centers with more than 500 m² per floor, buildings where more than 3,000 people work or live, and government buildings. Group I: everything else, such as housing and ordinary offices.
More than force
The occupancy group also sets the minimum performance of the nonstructural elements: superior for groups IV and III, good for group II and low for group I (table A.9.2-1). A hospital must keep operating after the earthquake; that is why its walls, ceilings and equipment are designed not to fail. We explain it in nonstructural elements.
It can move up a group
The owner may ask for the building to be designed in a higher group for extra safety (A.2.5.1.2 e). And if an existing building's use changes to a higher group, the code requires that change to be assessed (A.10.1.3.2): a store that becomes a school must be reviewed.
Source: NSR-10, Title A, sections A.2.5 and A.9.2.
Frequently asked questions
What occupancy group is a school in?
Group III, community service buildings, with an importance factor of 1.25.
And a hospital?
If it has surgery, intensive care or an emergency department, group IV, with a factor of 1.50; if not, group II, with 1.10.
