Live Load / Imposed Load

Live load (also called imposed load) is the variable load on a structure due to occupancy, use, and movable contents — people, furniture, equipment, stored material, vehicles. Distinguished from dead load (permanent self-weight) and environmental loads (wind, seismic, snow), live load varies with time and use. IS 875 Part 2:1987 (still the current Indian code, even after the 2015 revision of other parts) gives uniformly distributed loads (UDL in kN/m²) and concentrated loads (kN) for every common occupancy.

For common Indian buildings: residential rooms 2.0 kN/m², residential balconies 3.0 kN/m², office working areas 2.5 kN/m², retail shops 4.0 kN/m², hotel public areas 4.0 kN/m², school classrooms 3.0 kN/m², library reading rooms 4.0 kN/m², library stack rooms 6.0 kN/m². These values include partition allowance for residential and most office areas. Heavy-occupancy areas like mercantile (5 kN/m²), industrial floors (5-10 kN/m²), and stage platforms (5 kN/m²) require explicit calculation. Where storage occurs, IS 875 Part 2 specifies 25 kN/m² minimum, with explicit calculation for known storage densities.

For multi-storey buildings, IS 875 Part 2 Cl. 3.2 permits live load reduction with floor area and number of floors — for example, a column supporting 6 floors of office space can be designed for live load multiplied by reduction factor (typically 0.65-0.75). Without this reduction, the column would be massively oversized for a load case that statistically never occurs (full LL on every floor simultaneously). For seismic design per IS 1893 Cl. 7.3.1, only 25-50% of live load is included in seismic mass calculation — the assumption being most occupants and furniture will not contribute fully to inertia.